Larvaceans, class Appendicularia, are solitary, free-swimming tunicates found throughout the world's oceans. Like most tunicates, larvaceans are filter feeders. Unlike most other tunicates, they live in the pelagic zone, specifically in the photic zone, or sometimes deeper. They are transparent planktonic animals, generally less than 1 cm (0.39 in) in body length, excluding the tail.
The adult larvaceans resemble the tadpole-like larvae of most tunicates. Like a common tunicate larva, the adult Appendicularia have a discrete trunk and tail.
Larvaceans produce a "house" made of mucopolysaccharides and cellulose.[1] In most species, the house surrounds the animal like a bubble. Even for species in which the house does not completely surround the body, such as Fritillaria, the house is always present and attached to at least one surface.
These houses are discarded and replaced regularly as the animal grows in size and its filters become clogged; in Oikopleura, a house is kept for no more than four hours before being replaced. No other tunicate is able to abandon its test in this fashion. Discarded larvacean houses account for a significant fraction of organic material descending to the ocean depths.[2]
The tail of larvaceans contain a central notochord, a dorsal nerve cord, and a series of striated muscle bands enveloped either by epithelial tissue (oikopleurids) or by an acellular basement membrane (fritillarids). Unlike the Ascidiacea larvae, the tail nerve cord in larvaceans contain some neurons.[3]
Feeding
Larvaceans have greatly improved the efficiency of food intake by producing a test, which contains a complicated arrangement of filters that allow food in the surrounding water to be brought in and concentrated prior to feeding. By regularly beating the tail, the larvacean can generate water currents within its house that allow the concentration of food. The high efficiency of this method allows larvaceans to feed on much smaller nanoplankton than most other filter feeders.
Like most tunicates, larvaceans feed by drawing particulate food matter into their pharyngobranchial region, where food particles are trapped on a mucus mesh produced by the pharynx and drawn into the digestive tract. The mucus mesh lies over two clefts in the pharynx, one on either side, rather than the much larger number of clefts found in most other tunicates.
Furthermore, the Appendicularia retain the ancestral Chordate characteristics of having the clefts, and the anus open directly to the outside, and by the lack of the atrium and the atrial siphon found in related classes.
Reproduction and genetics
Larvaceans reproduce sexually. The immature animals resemble the tadpole larvae of ascidians, albeit with the addition of developing viscera. Once the trunk is fully developed, the larva undergoes "tail shift", in which the tail moves from a rearward position to a ventral orientation and twists 90° relative to the trunk. Following tail shift, the larvacean begins secretion of the first house.
Fertilisation is external. During egg release the body wall ruptures, killing the animal.[4]
The recent development of techniques for expressing foreign genes in Oikopleura dioica, which unlike all other known larvaceans have separate sexes instead of being a protandric hermaphrodite, has led to the advancement of this species as a model organism for the study of gene regulation, chordate evolution, and development.
References
^Increased fitness of a key appendicularian zooplankton species under warmer, acidified seawater conditions
^Robison, B.H.; Reisenbichler, K.R.; Sherlock, R.E. (2005). "Giant larvacean houses: Rapid carbon transport to the deep sea floor". Science. 308 (5758): 1609–1611. doi:10.1126/science.1109104. PMID 15947183.
^Kaas, Jon H. (2016). Evolution of nervous systems. Elsevier Science. pp. 14ff. ISBN978-0-12-804096-6.
^A review of the life cycles and life-history adaptations of pelagic tunicates to environmental conditions
Bone, Q. (1998). The Biology of Pelagic Tunicates. Oxford, UK: Oxford University Press.
Clarke, T.; Bouquet, JM; Fu, X; Kallesøe, T.; Schmid, M; Thompson, E.M. (2007). "Rapidly evolving lamins in a chordate, Oikopleura dioica, with unusual nuclear architecture". Gene. 396 (1): 159–169. doi:10.1016/j.gene.2007.03.006. PMID 17449201.
larvacea, appendicularia, redirects, here, plant, genus, appendicularia, plant, class, appendicularia, solitary, free, swimming, tunicates, found, throughout, world, oceans, like, most, tunicates, larvaceans, filter, feeders, unlike, most, other, tunicates, th. Appendicularia redirects here For the plant genus see Appendicularia plant Larvaceans class Appendicularia are solitary free swimming tunicates found throughout the world s oceans Like most tunicates larvaceans are filter feeders Unlike most other tunicates they live in the pelagic zone specifically in the photic zone or sometimes deeper They are transparent planktonic animals generally less than 1 cm 0 39 in in body length excluding the tail AppendiculariaOikopleura dioicaScientific classificationKingdom AnimaliaPhylum ChordataSubphylum TunicataClass AppendiculariaLahille 1890Order CopelataFamiliesKowalevskiidae Lahille 1888 Kowalevskia Fol 1872 Fritillariidae Seeliger 1895 Appendicularia Fol 1874 Tectillaria Lohmann amp Buckman 1926 Fritillaria Quoy amp Gaimard 1835 Oikopleuridae Lahille 1887 Bathochordaeus Chun 1900 Mesochordaeus Fenaux amp Youngbluth 1990 Althoffia Lohmann 1892 Mesoikopleura Fenaux 1993 Pelagopleura Lohmann 1926 Sinisteroffia Tokioka 1957 Chunopleura Lohmann 1914 Folia Lohmann 1892 Megalocercus Chun 1887 Oikopleura Mertens 1830 Stegosoma Chun 1887SynonymsLarvacea Herdman 1891Perennichordata Balfour 1881 Contents 1 Anatomy 2 Feeding 3 Reproduction and genetics 4 ReferencesAnatomy EditThe adult larvaceans resemble the tadpole like larvae of most tunicates Like a common tunicate larva the adult Appendicularia have a discrete trunk and tail Larvaceans produce a house made of mucopolysaccharides and cellulose 1 In most species the house surrounds the animal like a bubble Even for species in which the house does not completely surround the body such as Fritillaria the house is always present and attached to at least one surface These houses are discarded and replaced regularly as the animal grows in size and its filters become clogged in Oikopleura a house is kept for no more than four hours before being replaced No other tunicate is able to abandon its test in this fashion Discarded larvacean houses account for a significant fraction of organic material descending to the ocean depths 2 The tail of larvaceans contain a central notochord a dorsal nerve cord and a series of striated muscle bands enveloped either by epithelial tissue oikopleurids or by an acellular basement membrane fritillarids Unlike the Ascidiacea larvae the tail nerve cord in larvaceans contain some neurons 3 Feeding EditLarvaceans have greatly improved the efficiency of food intake by producing a test which contains a complicated arrangement of filters that allow food in the surrounding water to be brought in and concentrated prior to feeding By regularly beating the tail the larvacean can generate water currents within its house that allow the concentration of food The high efficiency of this method allows larvaceans to feed on much smaller nanoplankton than most other filter feeders Like most tunicates larvaceans feed by drawing particulate food matter into their pharyngobranchial region where food particles are trapped on a mucus mesh produced by the pharynx and drawn into the digestive tract The mucus mesh lies over two clefts in the pharynx one on either side rather than the much larger number of clefts found in most other tunicates Furthermore the Appendicularia retain the ancestral Chordate characteristics of having the clefts and the anus open directly to the outside and by the lack of the atrium and the atrial siphon found in related classes Reproduction and genetics EditLarvaceans reproduce sexually The immature animals resemble the tadpole larvae of ascidians albeit with the addition of developing viscera Once the trunk is fully developed the larva undergoes tail shift in which the tail moves from a rearward position to a ventral orientation and twists 90 relative to the trunk Following tail shift the larvacean begins secretion of the first house Fertilisation is external During egg release the body wall ruptures killing the animal 4 The recent development of techniques for expressing foreign genes in Oikopleura dioica which unlike all other known larvaceans have separate sexes instead of being a protandric hermaphrodite has led to the advancement of this species as a model organism for the study of gene regulation chordate evolution and development References Edit Increased fitness of a key appendicularian zooplankton species under warmer acidified seawater conditions Robison B H Reisenbichler K R Sherlock R E 2005 Giant larvacean houses Rapid carbon transport to the deep sea floor Science 308 5758 1609 1611 doi 10 1126 science 1109104 PMID 15947183 Kaas Jon H 2016 Evolution of nervous systems Elsevier Science pp 14ff ISBN 978 0 12 804096 6 A review of the life cycles and life history adaptations of pelagic tunicates to environmental conditions Bone Q 1998 The Biology of Pelagic Tunicates Oxford UK Oxford University Press Clarke T Bouquet JM Fu X Kallesoe T Schmid M Thompson E M 2007 Rapidly evolving lamins in a chordate Oikopleura dioica with unusual nuclear architecture Gene 396 1 159 169 doi 10 1016 j gene 2007 03 006 PMID 17449201 Wikispecies has information related to Larvacea Retrieved from https en wikipedia org w index php title Larvacea amp oldid 1114758153, wikipedia, wiki, book, books, library,
