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Sea urchin

January 31, 2023

For other uses, see Sea Urchin (disambiguation).

Sea urchins (/ˈɜːrtʃɪnz/) are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to 5,000 meters (16,000 ft; 2,700 fathoms).[1] The spherical, hard shells (tests) of sea urchins are round and covered in spines, ranging in length from 3 to 10 cm (1 to 4 in), though the black sea urchin can have spines as long as 30 cm (12 in). Sea urchins move slowly, crawling with tube feet, and also propel themselves with their spines. Although algae are the primary diet, sea urchins also eat slow-moving (sessile) animals. Predators that eat sea urchins include a wide variety of fish, starfish, crabs, marine mammals. Sea urchins are also used as food especially in Japan.

Sea Urchin
Temporal range: Ordovician–Present
Tripneustes ventricosus and Echinometra viridis
Scientific classification
Kingdom: Animalia
Phylum: Echinodermata
Subphylum: Echinozoa
Class: Echinoidea
Leske, 1778
Subclasses

Like all echinoderms, adult sea urchins have fivefold symmetry, but their pluteus larvae feature bilateral (mirror) symmetry, indicating that the sea urchin belongs to the Bilateria group of animal phyla, which also comprises the chordates and the arthropods, the annelids and the molluscs, and are found in every ocean and in every climate, from the tropics to the polar regions, and inhabit marine benthic (sea bed) habitats, from rocky shores to hadal zone depths. The fossil record of the Echinoids dates from the Ordovician period, some 450 million years ago. The closest echinoderm relatives of the sea urchin are the sea cucumbers (Holothuroidea), both of which are deuterostomes, a clade that includes the chordates. (Sand dollars are a separate order in the sea urchin class Echinoidea.)

The animals have been studied since the 19th century as model organisms in developmental biology, as their embryos were easy to observe. That has continued with studies of their genomes because of their unusual fivefold symmetry and relationship to chordates. Species such as the slate pencil urchin are popular in aquariums, where they are useful for controlling algae. Fossil urchins have been used as protective amulets.

Diversity

See also: List of echinodermata orders

Sea urchins are members of the phylum Echinodermata, which also includes sea stars, sea cucumbers, sand dollars, brittle stars, and crinoids. Like other echinoderms, they have five-fold symmetry (called pentamerism) and move by means of hundreds of tiny, transparent, adhesive "tube feet". The symmetry is not obvious in the living animal, but is easily visible in the dried test.[2]

Specifically, the term "sea urchin" refers to the "regular echinoids", which are symmetrical and globular, and includes several different taxonomic groups, with two subclasses : Euechinoidea ("modern" sea urchins, including irregular ones) and Cidaroidea or "slate-pencil urchins", which have very thick, blunt spines, with algae and sponges growing on them. The "irregular" sea urchins are an infra-class inside the Euechinoidea, called Irregularia, and include Atelostomata and Neognathostomata. Irregular echinoids include: flattened sand dollars, sea biscuits, and heart urchins.[3]

Together with sea cucumbers (Holothuroidea), they make up the subphylum Echinozoa, which is characterized by a globoid shape without arms or projecting rays. Sea cucumbers and the irregular echinoids have secondarily evolved diverse shapes. Although many sea cucumbers have branched tentacles surrounding their oral openings, these have originated from modified tube feet and are not homologous to the arms of the crinoids, sea stars, and brittle stars.[2]

Description

 
Sea urchin anatomy based on Arbacia sp.

Urchins typically range in size from 3 to 10 cm (1 to 4 in), although the largest species can reach up to 36 cm (14 in).[4] They have a rigid, usually spherical body bearing moveable spines, which gives the class the name Echinoidea (from the Greek ἐχῖνος ekhinos 'spine').[5] The name urchin is an old word for hedgehog, which sea urchins resemble; they have archaically been called sea hedgehogs.[6][7] The name is derived from Old French herichun, from Latin ericius ('hedgehog').[8]

Like other echinoderms, sea urchin early larvae have bilateral symmetry,[9] but they develop five-fold symmetry as they mature. This is most apparent in the "regular" sea urchins, which have roughly spherical bodies with five equally sized parts radiating out from their central axes. The mouth is at the base of the animal and the anus at the top; the lower surface is described as "oral" and the upper surface as "aboral".[a][2]

Several sea urchins, however, including the sand dollars, are oval in shape, with distinct front and rear ends, giving them a degree of bilateral symmetry. In these urchins, the upper surface of the body is slightly domed, but the underside is flat, while the sides are devoid of tube feet. This "irregular" body form has evolved to allow the animals to burrow through sand or other soft materials.[4]

Systems

Musculoskeletal

Further information: Test (biology) and Tube feet

The internal organs are enclosed in a hard shell or test composed of fused plates of calcium carbonate covered by a thin dermis and epidermis. The test is referred to as an endoskeleton rather than exoskeleton even though it encloses almost all of the urchin. This is because it is covered with a thin layer of muscle and skin; sea urchins also do not need to molt the way invertebrates with true exoskeletons do, instead the plates forming the test grow as the animal does.

The test is rigid, and divides into five ambulacral grooves separated by five wider interambulacral areas. Each of these ten longitudinal columns consists of two sets of plates (thus comprising 20 columns in total). The ambulacral plates have pairs of tiny holes through which the tube feet extend.[10]

All of the plates are covered in rounded tubercles to which the spines are attached. The spines are used for defence and for locomotion and come in a variety of forms.[11] The inner surface of the test is lined by peritoneum.[4] Sea urchins convert aqueous carbon dioxide using a catalytic process involving nickel into the calcium carbonate portion of the test.[12]

Most species have two series of spines, primary (long) and secondary (short), distributed over the surface of the body, with the shortest at the poles and the longest at the equator. The spines are usually hollow and cylindrical. Contraction of the muscular sheath that covers the test causes the spines to lean in one direction or another, while an inner sheath of collagen fibres can reversibly change from soft to rigid which can lock the spine in one position. Located among the spines are several types of pedicellaria, moveable stalked structures with jaws.[2]

Sea urchins move by walking, using their many flexible tube feet in a way similar to that of starfish; regular sea urchins do not have any favourite walking direction.[13] The tube feet protrude through pairs of pores in the test, and are operated by a water vascular system; this works through hydraulic pressure, allowing the sea urchin to pump water into and out of the tube feet. During locomotion, the tube feet are assisted by the spines which can be used for pushing the body along or to lift the test off the substrate. Movement is generally related to feeding, with the red sea urchin (Mesocentrotus franciscanus) managing about 7.5 cm (3 in) a day when there is ample food, and up to 50 cm (20 in) a day where there is not. An inverted sea urchin can right itself by progressively attaching and detaching its tube feet and manipulating its spines to roll its body upright.[2] Some species bury themselves in soft sediment using their spines, and Paracentrotus lividus uses its jaws to burrow into soft rocks.[14]

  •  

    Test of an Echinus esculentus, a regular sea urchin

  •  

    Test of black sea urchin, showing tubercles and ambulacral plates (on right)

  •  

    Inner surface of test, showing pentagonal interambulacral plates on right, and holes for tube feet on left.

  •  

    Test of a Phyllacanthus imperialis, a cidaroid sea urchin. These are characterised by their big tubercles, bearing large radiola.

  •  

    Close-up of the test showing an ambulacral groove with its two rows of pore-pairs, between two interambulacra areas (green). The tubercles are non-perforated.

  •  

    Close-up of a cidaroid sea urchin apical disc: the 5 holes are the gonopores, and the central one is the anus ("periproct"). The biggest genital plate is the madreporite.[15]

Feeding and digestion

 
Dentition of a sea urchin

The mouth lies in the centre of the oral surface in regular urchins, or towards one end in irregular urchins. It is surrounded by lips of softer tissue, with numerous small, embedded bony pieces. This area, called the peristome, also includes five pairs of modified tube feet and, in many species, five pairs of gills.[4] The jaw apparatus consists of five strong arrow-shaped plates known as pyramids, the ventral surface of each of which has a toothband with a hard tooth pointing towards the centre of the mouth. Specialised muscles control the protrusion of the apparatus and the action of the teeth, and the animal can grasp, scrape, pull and tear.[2] The structure of the mouth and teeth have been found to be so efficient at grasping and grinding that similar structures have been tested for use in real-world applications.[16]

On the upper surface of the test at the aboral pole is a membrane, the periproct, which surrounds the anus. The periproct contains a variable number of hard plates, five of which, the genital plates, contain the gonopores, and one is modified to contain the madreporite, which is used to balance the water vascular system.[2]

 
Aristotle's lantern in a sea urchin, viewed in lateral section

The mouth of most sea urchins is made up of five calcium carbonate teeth or plates, with a fleshy, tongue-like structure within. The entire chewing organ is known as Aristotle's lantern from Aristotle's description in his History of Animals (translated by D'Arcy Thompson):

... the urchin has what we mainly call its head and mouth down below, and a place for the issue of the residuum up above. The urchin has, also, five hollow teeth inside, and in the middle of these teeth a fleshy substance serving the office of a tongue. Next to this comes the esophagus, and then the stomach, divided into five parts, and filled with excretion, all the five parts uniting at the anal vent, where the shell is perforated for an outlet ... In reality the mouth-apparatus of the urchin is continuous from one end to the other, but to outward appearance it is not so, but looks like a horn lantern with the panes of horn left out.

However, this has recently been proven to be a mistranslation. Aristotle's lantern is actually referring to the whole shape of sea urchins, which look like the ancient lamps of Aristotle's time.[17][18]

Heart urchins are unusual in not having a lantern. Instead, the mouth is surrounded by cilia that pull strings of mucus containing food particles towards a series of grooves around the mouth.[4]

 
Digestive and circulatory systems of a regular sea urchin:
a = anus ; m = madreporite ; s = aquifer canal ; r = radial canal ; p = podial ampulla ; k = test wall ; i = intestine ; b = mouth

The lantern, where present, surrounds both the mouth cavity and the pharynx. At the top of the lantern, the pharynx opens into the esophagus, which runs back down the outside of the lantern, to join the small intestine and a single caecum. The small intestine runs in a full circle around the inside of the test, before joining the large intestine, which completes another circuit in the opposite direction. From the large intestine, a rectum ascends towards the anus. Despite the names, the small and large intestines of sea urchins are in no way homologous to the similarly named structures in vertebrates.[4]

Digestion occurs in the intestine, with the caecum producing further digestive enzymes. An additional tube, called the siphon, runs beside much of the intestine, opening into it at both ends. It may be involved in resorption of water from food.[4]

Circulation and respiration

The water vascular system leads downwards from the madreporite through the slender stone canal to the ring canal, which encircles the oesophagus. Radial canals lead from here through each ambulacral area to terminate in a small tentacle that passes through the ambulacral plate near the aboral pole. Lateral canals lead from these radial canals, ending in ampullae. From here, two tubes pass through a pair of pores on the plate to terminate in the tube feet.[2]

Sea urchins possess a hemal system with a complex network of vessels in the mesenteries around the gut, but little is known of the functioning of this system.[2] However, the main circulatory fluid fills the general body cavity, or coelom. This coelomic fluid contains phagocytic coelomocytes, which move through the vascular and hemal systems and are involved in internal transport and gas exchange. The coelomocytes are an essential part of blood clotting, but also collect waste products and actively remove them from the body through the gills and tube feet.[4]

Most sea urchins possess five pairs of external gills attached to the peristomial membrane around their mouths. These thin-walled projections of the body cavity are the main organs of respiration in those urchins that possess them. Fluid can be pumped through the gills' interiors by muscles associated with the lantern, but this does not provide a continuous flow, and occurs only when the animal is low in oxygen. Tube feet can also act as respiratory organs, and are the primary sites of gas exchange in heart urchins and sand dollars, both of which lack gills. The inside of each tube foot is divided by a septum which reduces diffusion between the incoming and outgoing streams of fluid.[2]

Nervous system and senses

The nervous system of sea urchins has a relatively simple layout. With no true brain, the neural center is a large nerve ring encircling the mouth just inside the lantern. From the nerve ring, five nerves radiate underneath the radial canals of the water vascular system, and branch into numerous finer nerves to innervate the tube feet, spines, and pedicellariae.[4]

Sea urchins are sensitive to touch, light, and chemicals. There are numerous sensitive cells in the epithelium, especially in the spines, pedicellaria and tube feet, and around the mouth.[2] Although they do not have eyes or eye spots (except for diadematids, which can follow a threat with their spines), the entire body of most regular sea urchins might function as a compound eye.[19] In general, sea urchins are negatively attracted to light, and seek to hide themselves in crevices or under objects. Most species, apart from pencil urchins, have statocysts in globular organs called spheridia. These are stalked structures and are located within the ambulacral areas; their function is to help in gravitational orientation.[4]

Life history

Reproduction

Male flower urchin (Toxopneustes roseus) releasing milt, November 1, 2011, Lalo Cove, Sea of Cortez

Sea urchins are dioecious, having separate male and female sexes, although no distinguishing features are visible externally. In addition to their role in reproduction, the gonads are also nutrient storing organs, and are made up of two main type of cells: germ cells, and somatic cells called nutritive phagocytes.[20] Regular sea urchins have five gonads, lying underneath the interambulacral regions of the test, while the irregular forms mostly have four, with the hindmost gonad being absent; heart urchins have three or two. Each gonad has a single duct rising from the upper pole to open at a gonopore lying in one of the genital plates surrounding the anus. Some burrowing sand dollars have an elongated papilla that enables the liberation of gametes above the surface of the sediment.[2] The gonads are lined with muscles underneath the peritoneum, and these allow the animal to squeeze its gametes through the duct and into the surrounding sea water, where fertilization takes place.[4]

Development

 
Sea urchin blastula

During early development, the sea urchin embryo undergoes 10 cycles of cell division,[21] resulting in a single epithelial layer enveloping the blastocoel. The embryo then begins gastrulation, a multipart process which dramatically rearranges its structure by invagination to produce the three germ layers, involving an epithelial-mesenchymal transition; primary mesenchyme cells move into the blastocoel[22] and become mesoderm.[23] It has been suggested that epithelial polarity together with planar cell polarity might be sufficient to drive gastrulation in sea urchins.[24]

 
The development of a regular sea urchin

An unusual feature of sea urchin development is the replacement of the larva's bilateral symmetry by the adult's broadly fivefold symmetry. During cleavage, mesoderm and small micromeres are specified. At the end of gastrulation, cells of these two types form coelomic pouches. In the larval stages, the adult rudiment grows from the left coelomic pouch; after metamorphosis, that rudiment grows to become the adult. The animal-vegetal axis is established before the egg is fertilized. The oral-aboral axis is specified early in cleavage, and the left-right axis appears at the late gastrula stage.[25]

Life cycle and development

 
Pluteus larva has bilateral symmetry.

In most cases, the female's eggs float freely in the sea, but some species hold onto them with their spines, affording them a greater degree of protection. The unfertilized egg meets with the free-floating sperm released by males, and develops into a free-swimming blastula embryo in as few as 12 hours. Initially a simple ball of cells, the blastula soon transforms into a cone-shaped echinopluteus larva. In most species, this larva has 12 elongated arms lined with bands of cilia that capture food particles and transport them to the mouth. In a few species, the blastula contains supplies of nutrient yolk and lacks arms, since it has no need to feed.[4]

Several months are needed for the larva to complete its development, the change into the adult form beginning with the formation of test plates in a juvenile rudiment which develops on the left side of the larva, its axis being perpendicular to that of the larva. Soon, the larva sinks to the bottom and metamorphoses into a juvenile urchin in as little as one hour.[2] In some species, adults reach their maximum size in about five years.[4] The purple urchin becomes sexually mature in two years and may live for twenty.[26]

Ecology

Trophic level

Sea urchin in natural habitat

Sea urchins feed mainly on algae, so they are primarily herbivores, but can feed on sea cucumbers and a wide range of invertebrates, such as mussels, polychaetes, sponges, brittle stars, and crinoids, making them omnivores, consumers at a range of trophic levels.[27]

Predators, parasites, and diseases

Mass mortality of sea urchins was first reported in the 1970s, but diseases in sea urchins had been little studied before the advent of aquaculture. In 1981, bacterial "spotting disease" caused almost complete mortality in juvenile Pseudocentrotus depressus and Hemicentrotus pulcherrimus, both cultivated in Japan; the disease recurred in succeeding years. It was divided into a cool-water "spring" disease and a hot-water "summer" form.[28] Another condition, bald sea urchin disease, causes loss of spines and skin lesions and is believed to be bacterial in origin.[29]

Adult sea urchins are usually well protected against most predators by their strong and sharp spines, which can be venomous in some species.[30] The small urchin clingfish lives among the spines of urchins such as Diadema; juveniles feed on the pedicellariae and sphaeridia, adult males choose the tube feet and adult females move away to feed on shrimp eggs and molluscs.[31]

Sea urchins are one of the favourite foods of many lobsters, crabs, triggerfish, California sheephead, sea otter and wolf eels (which specialise in sea urchins). All these animals carry particular adaptations (teeth, pincers, claws) and a strength that allow them to overcome the excellent protective features of sea urchins. Left unchecked by predators, urchins devastate their environments, creating what biologists call an urchin barren, devoid of macroalgae and associated fauna.[32] Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die. Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem. Sea otters have re-entered British Columbia, dramatically improving coastal ecosystem health.[33]

Anti-predator defences

 
The flower urchin is a dangerous, potentially lethally venomous species.

The spines, long and sharp in some species, protect the urchin from predators. Some tropical sea urchins like Diadematidae, Echinothuriidae and Toxopneustidae have venomous spines. Other creatures also make use of these defences; crabs, shrimps and other organisms shelter among the spines, and often adopt the colouring of their host. Some crabs in the Dorippidae family carry sea urchins, starfish, sharp shells or other protective objects in their claws.[34]

Pedicellaria[35] are a good means of defense against ectoparasites, but not a panacea as some of them actually feed on it.[36] The hemal system defends against endoparasites.[37]

Range and habitat

Sea urchins are established in most seabed habitats from the intertidal downwards, at an extremely wide range of depths.[38] Some species, such as Cidaris abyssicola, can live at depths of several kilometres. Many genera are found in only the abyssal zone, including many cidaroids, most of the genera in the Echinothuriidae family, and the "cactus urchins" Dermechinus. One of the deepest-living families is the Pourtalesiidae,[39] strange bottle-shaped irregular sea urchins that live in only the hadal zone and have been collected as deep as 6850 metres beneath the surface in the Sunda Trench.[40] Nevertheless, this makes sea urchin the class of echinoderms living the least deep, compared to brittle stars, starfish and crinoids that remain abundant below 8,000 m (26,250 ft) and sea cucumbers which have been recorded from 10,687 m (35,100 ft).[40]

Population densities vary by habitat, with more dense populations in barren areas as compared to kelp stands.[41][42] Even in these barren areas, greatest densities are found in shallow water. Populations are generally found in deeper water if wave action is present.[42] Densities decrease in winter when storms cause them to seek protection in cracks and around larger underwater structures.[42] The shingle urchin (Colobocentrotus atratus), which lives on exposed shorelines, is particularly resistant to wave action. It is one of the few sea urchin that can survive many hours out of water.[43]

Sea urchins can be found in all climates, from warm seas to polar oceans.[38] The larvae of the polar sea urchin Sterechinus neumayeri have been found to use energy in metabolic processes twenty-five times more efficiently than do most other organisms.[44] Despite their presence in nearly all the marine ecosystems, most species are found on temperate and tropical coasts, between the surface and some tens of meters deep, close to photosynthetic food sources.[38]

Evolution

Fossil history

 
The thick spines (radiola) of Cidaridae were used for walking on the soft seabed.

The earliest echinoid fossils date to the Middle Ordovician period (circa 465 Mya).[45][46][47] There is a rich fossil record, their hard tests made of calcite plates surviving in rocks from every period since then.[48] Spines are present in some well-preserved specimens, but usually only the test remains. Isolated spines are common as fossils. Some Jurassic and Cretaceous Cidaroida had very heavy, club-shaped spines.[49]

Most fossil echinoids from the Paleozoic era are incomplete, consisting of isolated spines and small clusters of scattered plates from crushed individuals, mostly in Devonian and Carboniferous rocks. The shallow-water limestones from the Ordovician and Silurian periods of Estonia are famous for echinoids.[50] Paleozoic echinoids probably inhabited relatively quiet waters. Because of their thin tests, they would certainly not have survived in the wave-battered coastal waters inhabited by many modern echinoids.[50] Echinoids declined to near extinction at the end of the Paleozoic era, with just six species known from the Permian period. Only two lineages survived this period's massive extinction and into the Triassic: the genus Miocidaris, which gave rise to modern cidaroida (pencil urchins), and the ancestor that gave rise to the euechinoids. By the upper Triassic, their numbers increased again. Cidaroids have changed very little since the Late Triassic, and are the only Paleozoic echinoid group to have survived.[50]

The euechinoids diversified into new lineages in the Jurassic and Cretaceous periods, and from them emerged the first irregular echinoids (the Atelostomata) during the early Jurassic.[51]

Some echinoids, such as Micraster in the chalk of the Cretaceous period, serve as zone or index fossils. Because they are abundant and evolved rapidly, they enable geologists to date the surrounding rocks.[52]

In the Paleogene and Neogene periods (circa 66 to 1.8 Mya), sand dollars (Clypeasteroida) arose. Their distinctive, flattened tests and tiny spines were adapted to life on or under loose sand in shallow water, and they are abundant as fossils in southern European limestones and sandstones.[50]

Phylogeny

External

Echinoids are deuterostome animals, like the chordates. A 2014 analysis of 219 genes from all classes of echinoderms gives the following phylogenetic tree.[53] Approximate dates of branching of major clades are shown in millions of years ago (mya).

Bilateria
Xenacoelomorpha

 

Nephrozoa
Deuterostomia
Chordata and allies

 

Echinodermata
Echinozoa
Holothuroidea

 

 Sea cucumbers 
Echinoidea

 

c. 450 mya
Asterozoa
Ophiuroidea

 

Brittle stars
Asteroidea

 

Starfish
Crinoidea

 

Crinoids
c. 500 mya
>540 mya
Protostomia
610 mya
650 mya

Internal

The phylogeny of the sea urchins is as follows:[54][55]

The phylogenetic study from 2022 presents a different topology of the Euechinoidea phylogenetic tree. Irregularia are sister group of Echinacea (including Salenioida) forming a common clade Carinacea, basal groups Aspidodiadematoida, Diadematoida, Echinothurioida, Micropygoida, and Pedinoida are comprised in a common basal clade Aulodonta.[56]

Relation to humans

Injuries

Main article: Sea urchin injury
 
Sea urchin injury on the top side of the foot. This injury resulted in some skin staining from the natural purple-black dye of the urchin.

Sea urchin injuries are puncture wounds inflicted by the animal's brittle, fragile spines.[57] These are a common source of injury to ocean swimmers, especially along coastal surfaces where coral with stationary sea urchins are present. Their stings vary in severity depending on the species. Their spines can be venomous or cause infection. Granuloma and staining of the skin from the natural dye inside the sea urchin can also occur. Breathing problems may indicate a serious reaction to toxins in the sea urchin.[58] They inflict a painful wound when they penetrate human skin, but are not themselves dangerous if fully removed promptly; if left in the skin, further problems may occur.[59]

Science

Sea urchins are traditional model organisms in developmental biology. This use originated in the 1800s, when their embryonic development became easily viewed by microscopy. The transparency of the urchin's eggs enabled them to be used to observe that sperm cells actually fertilize ova.[60] They continue to be used for embryonic studies, as prenatal development continues to seek testing for fatal diseases. Sea urchins are being used in longevity studies for comparison between the young and old of the species, particularly for their ability to regenerate tissue as needed.[61] Scientists at the University of St Andrews have discovered a genetic sequence, the '2A' region, in sea urchins previously thought to have belonged only to viruses that afflict humans like foot-and-mouth disease virus.[62] More recently, Eric H. Davidson and Roy John Britten argued for the use of urchins as a model organism due to their easy availability, high fecundity, and long lifespan. Beyond embryology, urchins provide an opportunity to research cis-regulatory elements.[63] Oceanography has taken an interest in monitoring the health of urchins and their populations as a way to assess overall ocean acidification,[64] temperatures, and ecological impacts.

The organism's evolutionary placement and unique embryology with five-fold symmetry were the major arguments in the proposal to seek the sequencing of its genome. Importantly, urchins act as the closest living relative to chordates and thus are of interest for the light they can shed on the evolution of vertebrates.[65] The genome of Strongylocentrotus purpuratus was completed in 2006 and established homology between sea urchin and vertebrate immune system-related genes. Sea urchins code for at least 222 Toll-like receptor genes and over 200 genes related to the Nod-like-receptor family found in vertebrates.[66] This increases its usefulness as a valuable model organism for studying the evolution of innate immunity. The sequencing also revealed that while some genes were thought to be limited to vertebrates, there were also innovations that have previously never been seen outside the chordate classification, such as immune transcription factors PU.1 and SPIB.[65]

As food

The gonads of both male and female sea urchins, usually called sea urchin roe or corals,[67] are culinary delicacies in many parts of the world, especially Japan.[68][69][70] In Japan, sea urchin is known as uni (うに), and its roe can retail for as much as ¥40,000 ($360) per kilogram;[71] it is served raw as sashimi or in sushi, with soy sauce and wasabi. Japan imports large quantities from the United States, South Korea, and other producers. Japan consumes 50,000 tons annually, amounting to over 80% of global production.[72] Japanese demand for sea urchins has raised concerns about overfishing.[73] In Mediterranean cuisines, Paracentrotus lividus is often eaten raw, or with lemon,[74] and known as ricci on Italian menus where it is sometimes used in pasta sauces. It can also flavour omelettes, scrambled eggs, fish soup,[75] mayonnaise, béchamel sauce for tartlets,[76] the boullie for a soufflé,[77] or Hollandaise sauce to make a fish sauce.[78] In Chilean cuisine, it is served raw with lemon, onions, and olive oil. Though the edible Strongylocentrotus droebachiensis is found in the North Atlantic, it is not widely eaten. However, sea urchins (called uutuk in Alutiiq) are commonly eaten by the Alaska Native population around Kodiak Island. It is commonly exported, mostly to Japan.[79] In the West Indies, slate pencil urchins are eaten.[68] On the Pacific Coast of North America, Strongylocentrotus franciscanus was praised by Euell Gibbons; Strongylocentrotus purpuratus is also eaten.[68]Native Americans in California are also known to eat sea urchins.[80] The coast of Southern California is known as a source of high quality uni, with divers picking sea urchin from kelp beds in depths as deep as 24 m/80 ft.[81] As of 2013, the state was limiting the practice to 300 sea urchin diver licenses.[81] In New Zealand, Evechinus chloroticus, known as kina in Māori, is a delicacy, traditionally eaten raw. Though New Zealand fishermen would like to export them to Japan, their quality is too variable.[82]

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    Sea urchin (uni) as sashimi with a dab of wasabi

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    Japanese uni-ikura don, sea urchin egg and salmon egg donburi

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    Open sea urchins in Sicily

Aquaria

 
A fossil sea urchin found on a Middle Saxon site in Lincolnshire, thought to have been used as an amulet[83]

Some species of sea urchins, such as the slate pencil urchin (Eucidaris tribuloides), are commonly sold in aquarium stores. Some species are effective at controlling filamentous algae, and they make good additions to an invertebrate tank.[84]

Folklore

A folk tradition in Denmark and southern England imagined sea urchin fossils to be thunderbolts, able to ward off harm by lightning or by witchcraft, as an apotropaic symbol.[85] Another version supposed they were petrified eggs of snakes, able to protect against heart and liver disease, poisons, and injury in battle, and accordingly they were carried as amulets. These were, according to the legend, created by magic from foam made by the snakes at midsummer.[86]

Explanatory notes

  1. ^ The tube feet are present in all parts of the animal except around the anus, so technically, the whole surface of the body should be considered to be the oral surface, with the aboral (non-mouth) surface limited to the immediate vicinity of the anus.[2]

References

  1. ^ "Animal Diversity Web – Echinoidea". University of Michigan Museum of Zoology. Retrieved 26 August 2012.
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External links

 
Wikimedia Commons has media related to Echinoidea.
  • World Register of Marine Species link: Echinoidea Leske, 1778 (+species list)
  • The sea urchin genome project
  • Also, (604) 524-0322.
  • The Echinoid Directory from the Natural History Museum.
  • at Stanford
  • California Sea Urchin commission
  • Introduction to the Echinoidea at UCMP Berkeley

January 31, 2023
urchin, other, uses, urchin, disambiguation, ɜːr, spiny, globular, echinoderms, class, echinoidea, about, species, urchin, live, seabed, every, ocean, inhabit, every, depth, zone, from, intertidal, seashore, down, meters, fathoms, spherical, hard, shells, test. For other uses see Sea Urchin disambiguation Sea urchins ˈ ɜːr tʃ ɪ n z are spiny globular echinoderms in the class Echinoidea About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to 5 000 meters 16 000 ft 2 700 fathoms 1 The spherical hard shells tests of sea urchins are round and covered in spines ranging in length from 3 to 10 cm 1 to 4 in though the black sea urchin can have spines as long as 30 cm 12 in Sea urchins move slowly crawling with tube feet and also propel themselves with their spines Although algae are the primary diet sea urchins also eat slow moving sessile animals Predators that eat sea urchins include a wide variety of fish starfish crabs marine mammals Sea urchins are also used as food especially in Japan Sea UrchinTemporal range Ordovician Present PreꞒ Ꞓ O S D C P T J K Pg NTripneustes ventricosus and Echinometra viridisScientific classificationKingdom AnimaliaPhylum EchinodermataSubphylum EchinozoaClass EchinoideaLeske 1778SubclassesSubclass Perischoechinoidea Order Cidaroida pencil urchins Subclass Euechinoidea Superorder Atelostomata Order Cassiduloida Order Spatangoida heart urchins Superorder Diadematacea Order Diadematoida Order Echinothurioida Order Pedinoida Superorder Echinacea Order Arbacioida Order Echinoida Order Phymosomatoida Order Salenioida Order Temnopleuroida Superorder Gnathostomata Order Clypeasteroida sand dollars Order HolectypoidaLike all echinoderms adult sea urchins have fivefold symmetry but their pluteus larvae feature bilateral mirror symmetry indicating that the sea urchin belongs to the Bilateria group of animal phyla which also comprises the chordates and the arthropods the annelids and the molluscs and are found in every ocean and in every climate from the tropics to the polar regions and inhabit marine benthic sea bed habitats from rocky shores to hadal zone depths The fossil record of the Echinoids dates from the Ordovician period some 450 million years ago The closest echinoderm relatives of the sea urchin are the sea cucumbers Holothuroidea both of which are deuterostomes a clade that includes the chordates Sand dollars are a separate order in the sea urchin class Echinoidea The animals have been studied since the 19th century as model organisms in developmental biology as their embryos were easy to observe That has continued with studies of their genomes because of their unusual fivefold symmetry and relationship to chordates Species such as the slate pencil urchin are popular in aquariums where they are useful for controlling algae Fossil urchins have been used as protective amulets Contents 1 Diversity 2 Description 3 Systems 3 1 Musculoskeletal 3 2 Feeding and digestion 3 3 Circulation and respiration 3 4 Nervous system and senses 4 Life history 4 1 Reproduction 4 2 Development 4 3 Life cycle and development 5 Ecology 5 1 Trophic level 5 2 Predators parasites and diseases 5 3 Anti predator defences 5 4 Range and habitat 6 Evolution 6 1 Fossil history 6 2 Phylogeny 6 2 1 External 6 2 2 Internal 7 Relation to humans 7 1 Injuries 7 2 Science 7 3 As food 7 4 Aquaria 7 5 Folklore 8 Explanatory notes 9 References 10 External linksDiversity EditSee also List of echinodermata orders Sea urchins are members of the phylum Echinodermata which also includes sea stars sea cucumbers sand dollars brittle stars and crinoids Like other echinoderms they have five fold symmetry called pentamerism and move by means of hundreds of tiny transparent adhesive tube feet The symmetry is not obvious in the living animal but is easily visible in the dried test 2 Specifically the term sea urchin refers to the regular echinoids which are symmetrical and globular and includes several different taxonomic groups with two subclasses Euechinoidea modern sea urchins including irregular ones and Cidaroidea or slate pencil urchins which have very thick blunt spines with algae and sponges growing on them The irregular sea urchins are an infra class inside the Euechinoidea called Irregularia and include Atelostomata and Neognathostomata Irregular echinoids include flattened sand dollars sea biscuits and heart urchins 3 Together with sea cucumbers Holothuroidea they make up the subphylum Echinozoa which is characterized by a globoid shape without arms or projecting rays Sea cucumbers and the irregular echinoids have secondarily evolved diverse shapes Although many sea cucumbers have branched tentacles surrounding their oral openings these have originated from modified tube feet and are not homologous to the arms of the crinoids sea stars and brittle stars 2 Paracentrotus lividus a regular sea urchin Euechinoidea infraclass Carinacea A sand dollar an irregular sea urchin Irregularia Phyllacanthus imperialis a cidaroid sea urchin Cidaroidea Description Edit Sea urchin anatomy based on Arbacia sp Urchins typically range in size from 3 to 10 cm 1 to 4 in although the largest species can reach up to 36 cm 14 in 4 They have a rigid usually spherical body bearing moveable spines which gives the class the name Echinoidea from the Greek ἐxῖnos ekhinos spine 5 The name urchin is an old word for hedgehog which sea urchins resemble they have archaically been called sea hedgehogs 6 7 The name is derived from Old French herichun from Latin ericius hedgehog 8 Like other echinoderms sea urchin early larvae have bilateral symmetry 9 but they develop five fold symmetry as they mature This is most apparent in the regular sea urchins which have roughly spherical bodies with five equally sized parts radiating out from their central axes The mouth is at the base of the animal and the anus at the top the lower surface is described as oral and the upper surface as aboral a 2 Several sea urchins however including the sand dollars are oval in shape with distinct front and rear ends giving them a degree of bilateral symmetry In these urchins the upper surface of the body is slightly domed but the underside is flat while the sides are devoid of tube feet This irregular body form has evolved to allow the animals to burrow through sand or other soft materials 4 Systems EditMusculoskeletal Edit Tube feet of a purple sea urchin Further information Test biology and Tube feet The internal organs are enclosed in a hard shell or test composed of fused plates of calcium carbonate covered by a thin dermis and epidermis The test is referred to as an endoskeleton rather than exoskeleton even though it encloses almost all of the urchin This is because it is covered with a thin layer of muscle and skin sea urchins also do not need to molt the way invertebrates with true exoskeletons do instead the plates forming the test grow as the animal does The test is rigid and divides into five ambulacral grooves separated by five wider interambulacral areas Each of these ten longitudinal columns consists of two sets of plates thus comprising 20 columns in total The ambulacral plates have pairs of tiny holes through which the tube feet extend 10 All of the plates are covered in rounded tubercles to which the spines are attached The spines are used for defence and for locomotion and come in a variety of forms 11 The inner surface of the test is lined by peritoneum 4 Sea urchins convert aqueous carbon dioxide using a catalytic process involving nickel into the calcium carbonate portion of the test 12 Most species have two series of spines primary long and secondary short distributed over the surface of the body with the shortest at the poles and the longest at the equator The spines are usually hollow and cylindrical Contraction of the muscular sheath that covers the test causes the spines to lean in one direction or another while an inner sheath of collagen fibres can reversibly change from soft to rigid which can lock the spine in one position Located among the spines are several types of pedicellaria moveable stalked structures with jaws 2 Sea urchins move by walking using their many flexible tube feet in a way similar to that of starfish regular sea urchins do not have any favourite walking direction 13 The tube feet protrude through pairs of pores in the test and are operated by a water vascular system this works through hydraulic pressure allowing the sea urchin to pump water into and out of the tube feet During locomotion the tube feet are assisted by the spines which can be used for pushing the body along or to lift the test off the substrate Movement is generally related to feeding with the red sea urchin Mesocentrotus franciscanus managing about 7 5 cm 3 in a day when there is ample food and up to 50 cm 20 in a day where there is not An inverted sea urchin can right itself by progressively attaching and detaching its tube feet and manipulating its spines to roll its body upright 2 Some species bury themselves in soft sediment using their spines and Paracentrotus lividus uses its jaws to burrow into soft rocks 14 Test of an Echinus esculentus a regular sea urchin Test of black sea urchin showing tubercles and ambulacral plates on right Inner surface of test showing pentagonal interambulacral plates on right and holes for tube feet on left Test of an Echinodiscus tenuissimus an irregular sea urchin sand dollar Test of a Phyllacanthus imperialis a cidaroid sea urchin These are characterised by their big tubercles bearing large radiola Close up of the test showing an ambulacral groove with its two rows of pore pairs between two interambulacra areas green The tubercles are non perforated Close up of a cidaroid sea urchin apical disc the 5 holes are the gonopores and the central one is the anus periproct The biggest genital plate is the madreporite 15 Feeding and digestion Edit Dentition of a sea urchin The mouth lies in the centre of the oral surface in regular urchins or towards one end in irregular urchins It is surrounded by lips of softer tissue with numerous small embedded bony pieces This area called the peristome also includes five pairs of modified tube feet and in many species five pairs of gills 4 The jaw apparatus consists of five strong arrow shaped plates known as pyramids the ventral surface of each of which has a toothband with a hard tooth pointing towards the centre of the mouth Specialised muscles control the protrusion of the apparatus and the action of the teeth and the animal can grasp scrape pull and tear 2 The structure of the mouth and teeth have been found to be so efficient at grasping and grinding that similar structures have been tested for use in real world applications 16 On the upper surface of the test at the aboral pole is a membrane the periproct which surrounds the anus The periproct contains a variable number of hard plates five of which the genital plates contain the gonopores and one is modified to contain the madreporite which is used to balance the water vascular system 2 Aristotle s lantern in a sea urchin viewed in lateral section The mouth of most sea urchins is made up of five calcium carbonate teeth or plates with a fleshy tongue like structure within The entire chewing organ is known as Aristotle s lantern from Aristotle s description in his History of Animals translated by D Arcy Thompson the urchin has what we mainly call its head and mouth down below and a place for the issue of the residuum up above The urchin has also five hollow teeth inside and in the middle of these teeth a fleshy substance serving the office of a tongue Next to this comes the esophagus and then the stomach divided into five parts and filled with excretion all the five parts uniting at the anal vent where the shell is perforated for an outlet In reality the mouth apparatus of the urchin is continuous from one end to the other but to outward appearance it is not so but looks like a horn lantern with the panes of horn left out However this has recently been proven to be a mistranslation Aristotle s lantern is actually referring to the whole shape of sea urchins which look like the ancient lamps of Aristotle s time 17 18 Heart urchins are unusual in not having a lantern Instead the mouth is surrounded by cilia that pull strings of mucus containing food particles towards a series of grooves around the mouth 4 Digestive and circulatory systems of a regular sea urchin a anus m madreporite s aquifer canal r radial canal p podial ampulla k test wall i intestine b mouth The lantern where present surrounds both the mouth cavity and the pharynx At the top of the lantern the pharynx opens into the esophagus which runs back down the outside of the lantern to join the small intestine and a single caecum The small intestine runs in a full circle around the inside of the test before joining the large intestine which completes another circuit in the opposite direction From the large intestine a rectum ascends towards the anus Despite the names the small and large intestines of sea urchins are in no way homologous to the similarly named structures in vertebrates 4 Digestion occurs in the intestine with the caecum producing further digestive enzymes An additional tube called the siphon runs beside much of the intestine opening into it at both ends It may be involved in resorption of water from food 4 Circulation and respiration Edit The water vascular system leads downwards from the madreporite through the slender stone canal to the ring canal which encircles the oesophagus Radial canals lead from here through each ambulacral area to terminate in a small tentacle that passes through the ambulacral plate near the aboral pole Lateral canals lead from these radial canals ending in ampullae From here two tubes pass through a pair of pores on the plate to terminate in the tube feet 2 Sea urchins possess a hemal system with a complex network of vessels in the mesenteries around the gut but little is known of the functioning of this system 2 However the main circulatory fluid fills the general body cavity or coelom This coelomic fluid contains phagocytic coelomocytes which move through the vascular and hemal systems and are involved in internal transport and gas exchange The coelomocytes are an essential part of blood clotting but also collect waste products and actively remove them from the body through the gills and tube feet 4 Most sea urchins possess five pairs of external gills attached to the peristomial membrane around their mouths These thin walled projections of the body cavity are the main organs of respiration in those urchins that possess them Fluid can be pumped through the gills interiors by muscles associated with the lantern but this does not provide a continuous flow and occurs only when the animal is low in oxygen Tube feet can also act as respiratory organs and are the primary sites of gas exchange in heart urchins and sand dollars both of which lack gills The inside of each tube foot is divided by a septum which reduces diffusion between the incoming and outgoing streams of fluid 2 Diadema setosum Nervous system and senses Edit The nervous system of sea urchins has a relatively simple layout With no true brain the neural center is a large nerve ring encircling the mouth just inside the lantern From the nerve ring five nerves radiate underneath the radial canals of the water vascular system and branch into numerous finer nerves to innervate the tube feet spines and pedicellariae 4 Sea urchins are sensitive to touch light and chemicals There are numerous sensitive cells in the epithelium especially in the spines pedicellaria and tube feet and around the mouth 2 Although they do not have eyes or eye spots except for diadematids which can follow a threat with their spines the entire body of most regular sea urchins might function as a compound eye 19 In general sea urchins are negatively attracted to light and seek to hide themselves in crevices or under objects Most species apart from pencil urchins have statocysts in globular organs called spheridia These are stalked structures and are located within the ambulacral areas their function is to help in gravitational orientation 4 Life history EditReproduction Edit source source source source source source Male flower urchin Toxopneustes roseus releasing milt November 1 2011 Lalo Cove Sea of Cortez Sea urchins are dioecious having separate male and female sexes although no distinguishing features are visible externally In addition to their role in reproduction the gonads are also nutrient storing organs and are made up of two main type of cells germ cells and somatic cells called nutritive phagocytes 20 Regular sea urchins have five gonads lying underneath the interambulacral regions of the test while the irregular forms mostly have four with the hindmost gonad being absent heart urchins have three or two Each gonad has a single duct rising from the upper pole to open at a gonopore lying in one of the genital plates surrounding the anus Some burrowing sand dollars have an elongated papilla that enables the liberation of gametes above the surface of the sediment 2 The gonads are lined with muscles underneath the peritoneum and these allow the animal to squeeze its gametes through the duct and into the surrounding sea water where fertilization takes place 4 Development Edit Sea urchin blastula During early development the sea urchin embryo undergoes 10 cycles of cell division 21 resulting in a single epithelial layer enveloping the blastocoel The embryo then begins gastrulation a multipart process which dramatically rearranges its structure by invagination to produce the three germ layers involving an epithelial mesenchymal transition primary mesenchyme cells move into the blastocoel 22 and become mesoderm 23 It has been suggested that epithelial polarity together with planar cell polarity might be sufficient to drive gastrulation in sea urchins 24 The development of a regular sea urchin An unusual feature of sea urchin development is the replacement of the larva s bilateral symmetry by the adult s broadly fivefold symmetry During cleavage mesoderm and small micromeres are specified At the end of gastrulation cells of these two types form coelomic pouches In the larval stages the adult rudiment grows from the left coelomic pouch after metamorphosis that rudiment grows to become the adult The animal vegetal axis is established before the egg is fertilized The oral aboral axis is specified early in cleavage and the left right axis appears at the late gastrula stage 25 Life cycle and development Edit Pluteus larva has bilateral symmetry In most cases the female s eggs float freely in the sea but some species hold onto them with their spines affording them a greater degree of protection The unfertilized egg meets with the free floating sperm released by males and develops into a free swimming blastula embryo in as few as 12 hours Initially a simple ball of cells the blastula soon transforms into a cone shaped echinopluteus larva In most species this larva has 12 elongated arms lined with bands of cilia that capture food particles and transport them to the mouth In a few species the blastula contains supplies of nutrient yolk and lacks arms since it has no need to feed 4 Several months are needed for the larva to complete its development the change into the adult form beginning with the formation of test plates in a juvenile rudiment which develops on the left side of the larva its axis being perpendicular to that of the larva Soon the larva sinks to the bottom and metamorphoses into a juvenile urchin in as little as one hour 2 In some species adults reach their maximum size in about five years 4 The purple urchin becomes sexually mature in two years and may live for twenty 26 Ecology EditTrophic level Edit source source source source source source Sea urchin in natural habitat Sea urchins feed mainly on algae so they are primarily herbivores but can feed on sea cucumbers and a wide range of invertebrates such as mussels polychaetes sponges brittle stars and crinoids making them omnivores consumers at a range of trophic levels 27 Predators parasites and diseases Edit Mass mortality of sea urchins was first reported in the 1970s but diseases in sea urchins had been little studied before the advent of aquaculture In 1981 bacterial spotting disease caused almost complete mortality in juvenile Pseudocentrotus depressus and Hemicentrotus pulcherrimus both cultivated in Japan the disease recurred in succeeding years It was divided into a cool water spring disease and a hot water summer form 28 Another condition bald sea urchin disease causes loss of spines and skin lesions and is believed to be bacterial in origin 29 Adult sea urchins are usually well protected against most predators by their strong and sharp spines which can be venomous in some species 30 The small urchin clingfish lives among the spines of urchins such as Diadema juveniles feed on the pedicellariae and sphaeridia adult males choose the tube feet and adult females move away to feed on shrimp eggs and molluscs 31 Sea urchins are one of the favourite foods of many lobsters crabs triggerfish California sheephead sea otter and wolf eels which specialise in sea urchins All these animals carry particular adaptations teeth pincers claws and a strength that allow them to overcome the excellent protective features of sea urchins Left unchecked by predators urchins devastate their environments creating what biologists call an urchin barren devoid of macroalgae and associated fauna 32 Sea urchins graze on the lower stems of kelp causing the kelp to drift away and die Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem Sea otters have re entered British Columbia dramatically improving coastal ecosystem health 33 Wolf eel a highly specialized predator of sea urchins A sea otter feeding on a purple sea urchin A crab Carpilius convexus attacking a slate pencil sea urchin Heterocentrotus mamillatus A wrasse finishing the remains of a damaged Tripneustes gratillaAnti predator defences Edit The flower urchin is a dangerous potentially lethally venomous species The spines long and sharp in some species protect the urchin from predators Some tropical sea urchins like Diadematidae Echinothuriidae and Toxopneustidae have venomous spines Other creatures also make use of these defences crabs shrimps and other organisms shelter among the spines and often adopt the colouring of their host Some crabs in the Dorippidae family carry sea urchins starfish sharp shells or other protective objects in their claws 34 Pedicellaria 35 are a good means of defense against ectoparasites but not a panacea as some of them actually feed on it 36 The hemal system defends against endoparasites 37 Range and habitat Edit Sea urchins are established in most seabed habitats from the intertidal downwards at an extremely wide range of depths 38 Some species such as Cidaris abyssicola can live at depths of several kilometres Many genera are found in only the abyssal zone including many cidaroids most of the genera in the Echinothuriidae family and the cactus urchins Dermechinus One of the deepest living families is the Pourtalesiidae 39 strange bottle shaped irregular sea urchins that live in only the hadal zone and have been collected as deep as 6850 metres beneath the surface in the Sunda Trench 40 Nevertheless this makes sea urchin the class of echinoderms living the least deep compared to brittle stars starfish and crinoids that remain abundant below 8 000 m 26 250 ft and sea cucumbers which have been recorded from 10 687 m 35 100 ft 40 Population densities vary by habitat with more dense populations in barren areas as compared to kelp stands 41 42 Even in these barren areas greatest densities are found in shallow water Populations are generally found in deeper water if wave action is present 42 Densities decrease in winter when storms cause them to seek protection in cracks and around larger underwater structures 42 The shingle urchin Colobocentrotus atratus which lives on exposed shorelines is particularly resistant to wave action It is one of the few sea urchin that can survive many hours out of water 43 Sea urchins can be found in all climates from warm seas to polar oceans 38 The larvae of the polar sea urchin Sterechinus neumayeri have been found to use energy in metabolic processes twenty five times more efficiently than do most other organisms 44 Despite their presence in nearly all the marine ecosystems most species are found on temperate and tropical coasts between the surface and some tens of meters deep close to photosynthetic food sources 38 Purple sea urchins at low tide in California They dig a cavity in the rock to hide from predators during the day Dermechinus horridus an abyssal species at thousands of meters deep Antarctic sea urchin Sterechinus neumayeri inhabits frozen seas The shape of the shingle urchin allows it to stay on wave beaten cliffs Evolution EditFossil history Edit The thick spines radiola of Cidaridae were used for walking on the soft seabed The earliest echinoid fossils date to the Middle Ordovician period circa 465 Mya 45 46 47 There is a rich fossil record their hard tests made of calcite plates surviving in rocks from every period since then 48 Spines are present in some well preserved specimens but usually only the test remains Isolated spines are common as fossils Some Jurassic and Cretaceous Cidaroida had very heavy club shaped spines 49 Most fossil echinoids from the Paleozoic era are incomplete consisting of isolated spines and small clusters of scattered plates from crushed individuals mostly in Devonian and Carboniferous rocks The shallow water limestones from the Ordovician and Silurian periods of Estonia are famous for echinoids 50 Paleozoic echinoids probably inhabited relatively quiet waters Because of their thin tests they would certainly not have survived in the wave battered coastal waters inhabited by many modern echinoids 50 Echinoids declined to near extinction at the end of the Paleozoic era with just six species known from the Permian period Only two lineages survived this period s massive extinction and into the Triassic the genus Miocidaris which gave rise to modern cidaroida pencil urchins and the ancestor that gave rise to the euechinoids By the upper Triassic their numbers increased again Cidaroids have changed very little since the Late Triassic and are the only Paleozoic echinoid group to have survived 50 The euechinoids diversified into new lineages in the Jurassic and Cretaceous periods and from them emerged the first irregular echinoids the Atelostomata during the early Jurassic 51 Some echinoids such as Micraster in the chalk of the Cretaceous period serve as zone or index fossils Because they are abundant and evolved rapidly they enable geologists to date the surrounding rocks 52 In the Paleogene and Neogene periods circa 66 to 1 8 Mya sand dollars Clypeasteroida arose Their distinctive flattened tests and tiny spines were adapted to life on or under loose sand in shallow water and they are abundant as fossils in southern European limestones and sandstones 50 Archaeocidaris brownwoodensis Cidaroida Carboniferous c 300 mya Miocidaris coaeva Cidaroida Middle Triassic c 240 mya Clypeus plotti Irregularia Middle Jurassic c 162 mya Echinocorys Holasteroida Upper Cretaceous c 80 mya Echinolampas ovalis Cassiduloida Middle Eocene c 40 mya Clypeaster portentosus Clypeasteroida Miocene c 10 myaPhylogeny Edit External Edit Echinoids are deuterostome animals like the chordates A 2014 analysis of 219 genes from all classes of echinoderms gives the following phylogenetic tree 53 Approximate dates of branching of major clades are shown in millions of years ago mya Bilateria Xenacoelomorpha Nephrozoa Deuterostomia Chordata and allies Echinodermata Echinozoa Holothuroidea Sea cucumbers Echinoidea c 450 myaAsterozoa Ophiuroidea Brittle starsAsteroidea StarfishCrinoidea Crinoidsc 500 mya gt 540 myaProtostomia Ecdysozoa Spiralia 610 mya650 myaInternal Edit The phylogeny of the sea urchins is as follows 54 55 Echinoidea Cidaroida Euechinoidea Echinothurioida Acroechinoidea Diadematoida Irregularia Pedinoida Salenioida Echinacea Stomopneustidae Arbaciidae Camarodonta Parasaleniidae Temnopleuridae TrigonocidaridaeEchinoida Echinidae Parechinidae Toxopneustidae Echinometridae Strongylocentrotidae 450 myaThe phylogenetic study from 2022 presents a different topology of the Euechinoidea phylogenetic tree Irregularia are sister group of Echinacea including Salenioida forming a common clade Carinacea basal groups Aspidodiadematoida Diadematoida Echinothurioida Micropygoida and Pedinoida are comprised in a common basal clade Aulodonta 56 Relation to humans EditInjuries Edit Main article Sea urchin injury Sea urchin injury on the top side of the foot This injury resulted in some skin staining from the natural purple black dye of the urchin Sea urchin injuries are puncture wounds inflicted by the animal s brittle fragile spines 57 These are a common source of injury to ocean swimmers especially along coastal surfaces where coral with stationary sea urchins are present Their stings vary in severity depending on the species Their spines can be venomous or cause infection Granuloma and staining of the skin from the natural dye inside the sea urchin can also occur Breathing problems may indicate a serious reaction to toxins in the sea urchin 58 They inflict a painful wound when they penetrate human skin but are not themselves dangerous if fully removed promptly if left in the skin further problems may occur 59 Science Edit Sea urchins are traditional model organisms in developmental biology This use originated in the 1800s when their embryonic development became easily viewed by microscopy The transparency of the urchin s eggs enabled them to be used to observe that sperm cells actually fertilize ova 60 They continue to be used for embryonic studies as prenatal development continues to seek testing for fatal diseases Sea urchins are being used in longevity studies for comparison between the young and old of the species particularly for their ability to regenerate tissue as needed 61 Scientists at the University of St Andrews have discovered a genetic sequence the 2A region in sea urchins previously thought to have belonged only to viruses that afflict humans like foot and mouth disease virus 62 More recently Eric H Davidson and Roy John Britten argued for the use of urchins as a model organism due to their easy availability high fecundity and long lifespan Beyond embryology urchins provide an opportunity to research cis regulatory elements 63 Oceanography has taken an interest in monitoring the health of urchins and their populations as a way to assess overall ocean acidification 64 temperatures and ecological impacts The organism s evolutionary placement and unique embryology with five fold symmetry were the major arguments in the proposal to seek the sequencing of its genome Importantly urchins act as the closest living relative to chordates and thus are of interest for the light they can shed on the evolution of vertebrates 65 The genome of Strongylocentrotus purpuratus was completed in 2006 and established homology between sea urchin and vertebrate immune system related genes Sea urchins code for at least 222 Toll like receptor genes and over 200 genes related to the Nod like receptor family found in vertebrates 66 This increases its usefulness as a valuable model organism for studying the evolution of innate immunity The sequencing also revealed that while some genes were thought to be limited to vertebrates there were also innovations that have previously never been seen outside the chordate classification such as immune transcription factors PU 1 and SPIB 65 As food Edit The gonads of both male and female sea urchins usually called sea urchin roe or corals 67 are culinary delicacies in many parts of the world especially Japan 68 69 70 In Japan sea urchin is known as uni うに and its roe can retail for as much as 40 000 360 per kilogram 71 it is served raw as sashimi or in sushi with soy sauce and wasabi Japan imports large quantities from the United States South Korea and other producers Japan consumes 50 000 tons annually amounting to over 80 of global production 72 Japanese demand for sea urchins has raised concerns about overfishing 73 In Mediterranean cuisines Paracentrotus lividus is often eaten raw or with lemon 74 and known as ricci on Italian menus where it is sometimes used in pasta sauces It can also flavour omelettes scrambled eggs fish soup 75 mayonnaise bechamel sauce for tartlets 76 the boullie for a souffle 77 or Hollandaise sauce to make a fish sauce 78 In Chilean cuisine it is served raw with lemon onions and olive oil Though the edible Strongylocentrotus droebachiensis is found in the North Atlantic it is not widely eaten However sea urchins called uutuk in Alutiiq are commonly eaten by the Alaska Native population around Kodiak Island It is commonly exported mostly to Japan 79 In the West Indies slate pencil urchins are eaten 68 On the Pacific Coast of North America Strongylocentrotus franciscanus was praised by Euell Gibbons Strongylocentrotus purpuratus is also eaten 68 Native Americans in California are also known to eat sea urchins 80 The coast of Southern California is known as a source of high quality uni with divers picking sea urchin from kelp beds in depths as deep as 24 m 80 ft 81 As of 2013 the state was limiting the practice to 300 sea urchin diver licenses 81 In New Zealand Evechinus chloroticus known as kina in Maori is a delicacy traditionally eaten raw Though New Zealand fishermen would like to export them to Japan their quality is too variable 82 Sea urchin uni as sashimi with a dab of wasabi Japanese uni ikura don sea urchin egg and salmon egg donburi Open sea urchins in SicilyAquaria Edit A fossil sea urchin found on a Middle Saxon site in Lincolnshire thought to have been used as an amulet 83 Some species of sea urchins such as the slate pencil urchin Eucidaris tribuloides are commonly sold in aquarium stores Some species are effective at controlling filamentous algae and they make good additions to an invertebrate tank 84 Folklore Edit A folk tradition in Denmark and southern England imagined sea urchin fossils to be thunderbolts able to ward off harm by lightning or by witchcraft as an apotropaic symbol 85 Another version supposed they were petrified eggs of snakes able to protect against heart and liver disease poisons and injury in battle and accordingly they were carried as amulets These were according to the legend created by magic from foam made by the snakes at midsummer 86 Explanatory notes Edit The tube feet are present in all parts of the animal except around the anus so technically the whole surface of the body should be considered to be the oral surface with the aboral non mouth surface 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September 2018 Sea Urchin Fishery and Overfishing TED Case Studies 296 American University full text for Puglia Italy Touring Club Italiano Guida all Italia gastronomica 1984 p 314 for Alexandria Egypt Claudia Roden A Book of Middle Eastern Food p 183 Alan Davidson Mediterranean Seafood p 270 Larousse Gastronomique page needed Curnonsky Cuisine et vins de France nouvelle edition 1974 p 248 Davidson Alan 2014 Oxford Companion to Food Oxford University Press 3rd edition p 280 Kleiman Dena October 3 1990 Scorned at Home Maine Sea Urchin Is a Star in Japan The New York Times p C1 Martin R E Carter E P Flick G J Davis L M 2000 Marine and Freshwater Products Handbook Taylor amp Francis p 268 ISBN 978 1 56676 889 4 Retrieved 2014 12 03 a b Lam Francis 2014 03 14 California Sea Urchin Divers Interviewed by Francis Lam Bon Appetit Retrieved 2017 03 26 Wassilieff Maggy March 2 2009 sea urchins Te Ara The Encyclopedia of New Zealand Amulet LIN B37563 Portable Antiquities Scheme Retrieved 14 March 2018 Tullock John H 2008 Your First Marine Aquarium Everything about Setting Up a Marine Aquarium Including Conditioning Maintenance Selecting Fish and Invertebrates and More Barron s Educational Series p 63 ISBN 978 0 7641 3675 7 McNamara Ken 2012 Prehistoric fossil collectors The Geological Society Retrieved 14 March 2018 Marren Peter Mabey Richard 2010 Bugs Britannica Chatto amp Windus pp 469 470 ISBN 978 0 7011 8180 2 External links Edit Wikimedia Commons has media related to Echinoidea World Register of Marine Species link Echinoidea Leske 1778 species list The sea urchin genome project Sea Urchin Harvesters Association California Also 604 524 0322 The Echinoid Directory from the Natural History Museum Virtual Urchin at Stanford California Sea Urchin commission Introduction to the Echinoidea at UCMP Berkeley Retrieved from https en wikipedia org w index php title Sea urchin amp oldid 1130900170, wikipedia, wiki, book, books, library,

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