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Tryblidiida

February 13, 2024

Tryblidiida is a taxon of monoplacophoran molluscans containing the only extant representatives: 37 species are still alive today, inhabiting the ocean at depths of between 175 and 6,400 metres (574 and 21,000 ft).[2]

Tryblidiida
Temporal range: Middle Pleistocene– Recent[1]
↓
The holotype of Neopilina galatheae at the Zoological Museum, Copenhagen
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Monoplacophora
Subclass: Tergomya
Order: Tryblidiida
Families

History of discoveries edit

The first captured living monoplacophoran was Veleropilina zografi in 1896, but at that time it was described as if it were an archaeogastropod, a true limpet, mainly because of its patelliform (limpet-like) shell. This species was finally revealed to be monoplacophoran 87 years later, in 1983.

In April 1952, a living specimen was collected from deep depths in the Middle America Trench off Costa Rica's Pacific coast.[3] In 1957 that species was described and named Neopilina galatheae by its discoverer, Danish biologist Henning Mourier Lemche (1904–1977).[4] An expert in the field has called this discovery "one of the greatest sensations in the [twentieth] century."[5] As of 2008, there were 31 living species known, discovered in waters from 200 meters in depth to hadal depths, or more than 6,000 meters in the deepest ocean trenches.[5][6]

The first specimen photographed alive was Vema hyalina, at a depth of 400 meters off Catalina Island, California, in 1977.[7] Scientists believe that the taxon Monoplacophora is probably polyphyletic and have proposed including all the living members in the order Tryblidiida.[5]

In 1989, fossils in Italy from the middle Pleistocene were described which appear to be identical with the living species Micropilina minuta.[8]

Anatomy edit

 
Drawing of the shell of Pilina unguis. Head region is on the left.
 
Ventral view of the (fossil) shell of Tryblidium reticulatum Lindström, 1880. There are visible muscular attachment scars. Head region is on the upper part of the drawing. The shell length is up to 43 mm.
 
Dorsal view of the shell of Tryblidium reticulatum.

Little is known about monoplacophorans. They have a single, flat, rounded bilateral shell that is often thin and fragile; it ranges in size from 3 to 30 millimetres (in recent species).[citation needed] The apex of the shell is at the anterior end. The fossil shells exhibit a series of muscular attachment scars on the inner side, suggesting metamerism; indeed, with living Monoplacophora to study, it can be seen that their body segments exhibit a serial repetition of kidneys, gills and reproductive structure. This used to be interpreted as a true segmentation, which suggested a "missing link" between mollusks and annelids. More recent studies have shown that the repetition of these organs is secondary.[citation needed]

Monoplacophorans move on a rounded foot. Their reduced head lacks eyes or tentacles.

The mantle cavity forms a horseshoe-shaped groove running around the muscular foot, in a similar fashion to that of the chitons, and contains five or six gills on either side. The mouth opens on the underside between the ends of the groove, while the anus opens into the hindmost part. Like chitons, monoplacophorans possess a sensory subradular organ, as well as a rasping radula. A fold of ciliated tissue surrounds the mouth to the front and sides, while a smaller fold, bearing a number of tentacles, lies just behind it. The stomach contains a style, projecting from a diverticulum, or "style sac".

The mouth has a chevron-shaped lip in front of it, and bears tentacles behind it, which have various shapes and layouts in different species.[2]

The heart is divided into two equal halves, each with its own auricle, ventricle and aorta. The left and right aorta fuse shortly after leaving the heart, and supply blood to the open circulatory system. There are six pairs of nephridial excretory organs, which empty into the mantle cavity.

The nervous system has small ganglia around the oesophagus from which two pairs of main nerve cords run through the body; one pair supplying the foot, and the other the visceral organs. As in the chitons, these main nerve cords are connected by a series of lateral nerves, giving the layout of the nervous system an appearance somewhat like a ladder.

There are two pairs of gonads, which release gametes into the water through one of the pairs of nephridia. The sexes are separate, and fertilisation is external.[9]

Ecology edit

Habitat edit

Monoplacophora are a geographically widespread component of the benthos. Most are known from deep water (1800 – 6500 meters), although several species are found in shallower waters ranging up to 200 meters.[10]

Feeding habits edit

It is presumed that they graze on microscopic organisms in mud or bottom detritus.

Taxonomy of extant species edit

Order Tryblidiida

References edit

  1. ^ TAVIANI, M., B. SABELLI, and F. CANDINI. 1990: A fossil Cenozoic monoplacophoran. Lethaia 23:213–216.
  2. ^ a b Lindberg, D. R. (2009). "Monoplacophorans and the Origin and Relationships of Mollusks" (PDF). Evolution: Education and Outreach. 2 (2): 191–203. doi:10.1007/s12052-009-0125-4.
  3. ^ Enrico Schwabe, A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora (Mollusca), Zootaxa 1866: 2005-222 (2008).
  4. ^ "New Pilina": Pilina was a monoplacophore that lived during Silurian times. Galathea was the name of the Danish research vessel that recovered it.
  5. ^ a b c Schwabe, above, at p. 205.
  6. ^ A list of species names is in WoRMS World Register of Marine Species
  7. ^ Lynn Margulis and Karlene V. Schwartz, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth (third edition (1997), p. 290).
  8. ^ Taviani, M.; Sabelli, B.; Candini, F. (1990). "A fossil Cenozoic monoplacophoran". Lethaia. 23 (2): 213–216. doi:10.1111/j.1502-3931.1990.tb01361.x.
  9. ^ Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 379–381. ISBN 0-03-056747-5.
  10. ^ Wingstrand, KG (1985). "On the anatomy and relationships of Recent Monoplacophora" (Link to free full text + plates). Galathea Report. 16: 7–94. Leiden & Copenhagen.
  11. ^ V. Urgorri, O. García-Álvarez and Á. Luque (2005). "Laevipilina Cachuchensis, A New Neopilinid (Mollusca: Tryblidia) From Off North Spain". Journal of Molluscan Studies. 71 (1): 59–66. doi:10.1093/mollus/eyi008.

February 13, 2024
tryblidiida, taxon, monoplacophoran, molluscans, containing, only, extant, representatives, species, still, alive, today, inhabiting, ocean, depths, between, metres, temporal, range, middle, pleistocene, recent, preꞒ, holotype, neopilina, galatheae, zoological. Tryblidiida is a taxon of monoplacophoran molluscans containing the only extant representatives 37 species are still alive today inhabiting the ocean at depths of between 175 and 6 400 metres 574 and 21 000 ft 2 TryblidiidaTemporal range Middle Pleistocene Recent 1 PreꞒ Ꞓ O S D C P T J K Pg N The holotype of Neopilina galatheae at the Zoological Museum CopenhagenScientific classificationDomain EukaryotaKingdom AnimaliaPhylum MolluscaClass MonoplacophoraSubclass TergomyaOrder TryblidiidaFamiliesLaevipilinidaeMicropilinidaeMonoplacophoridaeNeopilinidae Contents 1 History of discoveries 2 Anatomy 3 Ecology 3 1 Habitat 3 2 Feeding habits 4 Taxonomy of extant species 5 ReferencesHistory of discoveries editThe first captured living monoplacophoran was Veleropilina zografi in 1896 but at that time it was described as if it were an archaeogastropod a true limpet mainly because of its patelliform limpet like shell This species was finally revealed to be monoplacophoran 87 years later in 1983 In April 1952 a living specimen was collected from deep depths in the Middle America Trench off Costa Rica s Pacific coast 3 In 1957 that species was described and named Neopilina galatheae by its discoverer Danish biologist Henning Mourier Lemche 1904 1977 4 An expert in the field has called this discovery one of the greatest sensations in the twentieth century 5 As of 2008 there were 31 living species known discovered in waters from 200 meters in depth to hadal depths or more than 6 000 meters in the deepest ocean trenches 5 6 The first specimen photographed alive was Vema hyalina at a depth of 400 meters off Catalina Island California in 1977 7 Scientists believe that the taxon Monoplacophora is probably polyphyletic and have proposed including all the living members in the order Tryblidiida 5 In 1989 fossils in Italy from the middle Pleistocene were described which appear to be identical with the living species Micropilina minuta 8 Anatomy edit nbsp Drawing of the shell of Pilina unguis Head region is on the left nbsp Ventral view of the fossil shell of Tryblidium reticulatum Lindstrom 1880 There are visible muscular attachment scars Head region is on the upper part of the drawing The shell length is up to 43 mm nbsp Dorsal view of the shell of Tryblidium reticulatum Little is known about monoplacophorans They have a single flat rounded bilateral shell that is often thin and fragile it ranges in size from 3 to 30 millimetres in recent species citation needed The apex of the shell is at the anterior end The fossil shells exhibit a series of muscular attachment scars on the inner side suggesting metamerism indeed with living Monoplacophora to study it can be seen that their body segments exhibit a serial repetition of kidneys gills and reproductive structure This used to be interpreted as a true segmentation which suggested a missing link between mollusks and annelids More recent studies have shown that the repetition of these organs is secondary citation needed Monoplacophorans move on a rounded foot Their reduced head lacks eyes or tentacles The mantle cavity forms a horseshoe shaped groove running around the muscular foot in a similar fashion to that of the chitons and contains five or six gills on either side The mouth opens on the underside between the ends of the groove while the anus opens into the hindmost part Like chitons monoplacophorans possess a sensory subradular organ as well as a rasping radula A fold of ciliated tissue surrounds the mouth to the front and sides while a smaller fold bearing a number of tentacles lies just behind it The stomach contains a style projecting from a diverticulum or style sac The mouth has a chevron shaped lip in front of it and bears tentacles behind it which have various shapes and layouts in different species 2 The heart is divided into two equal halves each with its own auricle ventricle and aorta The left and right aorta fuse shortly after leaving the heart and supply blood to the open circulatory system There are six pairs of nephridial excretory organs which empty into the mantle cavity The nervous system has small ganglia around the oesophagus from which two pairs of main nerve cords run through the body one pair supplying the foot and the other the visceral organs As in the chitons these main nerve cords are connected by a series of lateral nerves giving the layout of the nervous system an appearance somewhat like a ladder There are two pairs of gonads which release gametes into the water through one of the pairs of nephridia The sexes are separate and fertilisation is external 9 Ecology editHabitat edit Monoplacophora are a geographically widespread component of the benthos Most are known from deep water 1800 6500 meters although several species are found in shallower waters ranging up to 200 meters 10 Feeding habits edit It is presumed that they graze on microscopic organisms in mud or bottom detritus Taxonomy of extant species editOrder Tryblidiida Family Laevipilinidae Genus Laevipilina J H McLean 1979 Laevipilina antarctica Waren amp Hain 1992 Laevipilina cachuchensis Urgorri Garcia Alvarez amp Luque 2005 11 Laevipilina hyalina J H McLean 1979 Laevipilina rolani Waren amp Bouchet 1990 Laevipilina theresae Schrodl 2006 Family Micropilinidae Genus Micropilina Waren 1989 Micropilina arntzi Waren amp Hain 1992 Micropilina minuta Waren 1989 Micropilina rakiura Marshall 1998 Micropilina reingi Marshall 2006 Micropilina tangaroa Marshall 1992 Micropilina wareni Marshall 2006 Family Monoplacophoridae Genus Monoplacophorus Moskalev Starobogatov amp Filatova 1983 Monoplacophorus zenkevitchi Moskalev Starobogatov amp Filatova 1983 Family Neopilinidae Genus Adenopilina Starobogatov amp Moskalev 1987 Adenopilina adenensis Tebble 1967 Genus Neopilina H Lemche 1957 Neopilina bruuni Menzies 1968 Neopilina galatheae Lemche 1957 Neopilina rebainsi Moskalev Starobogatov amp Filatova 1983 Neopilina starobogatovi Ivanov amp Moskalev 2007 Genus Rokopella Starobogatov amp Moskalev 1987 Rokopella brummeri Goud amp Gittenberger 1993 Rokopella capulus Marshall 2006 Rokopella euglypta Dautzenberg amp Fischer 1897 Rokopella goesi Waren 1988 Rokopella oligotropha Rokop 1972 Rokopella segonzaci Waren amp Bouchet 2001 Genus Veleropilina Starobogatov amp Moskalev 1987 Veleropilina brummeri Goud amp Gittenberger 1993 Veleropilina capulus B A Marshall 2006 Veleropilina euglypta Dautzenberg amp H Fischer 1897 Veleropilina goesi Waren 1988 Veleropilina oligotropha Rokop 1972 Veleropilina reticulata Seguenza 1876 Veleropilina segonzaci Waren amp Bouchet 2001 Veleropilina seisuimaruae Kano S Kimura T Kimura amp Waren 2012 Veleropilina veleronis Menzies amp Layton 1963 Veleropilina zografi Dautzenberg amp H Fischer 1896 Genus Vema Clarke amp Menzies 1959 Vema bacescui Menzies 1968 Vema ewingi Clarke amp Menzies 1959 Vema levinae Waren 1996 Vema occidua B A Marshall 2006References edit TAVIANI M B SABELLI and F CANDINI 1990 A fossil Cenozoic monoplacophoran Lethaia 23 213 216 a b Lindberg D R 2009 Monoplacophorans and the Origin and Relationships of Mollusks PDF Evolution Education and Outreach 2 2 191 203 doi 10 1007 s12052 009 0125 4 Enrico Schwabe A summary of reports of abyssal and hadal Monoplacophora and Polyplacophora Mollusca Zootaxa 1866 2005 222 2008 New Pilina Pilina was a monoplacophore that lived during Silurian times Galathea was the name of the Danish research vessel that recovered it a b c Schwabe above at p 205 A list of species names is in WoRMS World Register of Marine Species Lynn Margulis and Karlene V Schwartz Five Kingdoms An Illustrated Guide to the Phyla of Life on Earth third edition 1997 p 290 Taviani M Sabelli B Candini F 1990 A fossil Cenozoic monoplacophoran Lethaia 23 2 213 216 doi 10 1111 j 1502 3931 1990 tb01361 x Barnes Robert D 1982 Invertebrate Zoology Philadelphia PA Holt Saunders International pp 379 381 ISBN 0 03 056747 5 Wingstrand KG 1985 On the anatomy and relationships of Recent Monoplacophora Link to free full text plates Galathea Report 16 7 94 Leiden amp Copenhagen V Urgorri O Garcia Alvarez and A Luque 2005 Laevipilina Cachuchensis A New Neopilinid Mollusca Tryblidia From Off North Spain Journal of Molluscan Studies 71 1 59 66 doi 10 1093 mollus eyi008 Retrieved from https en wikipedia org w index php title Tryblidiida amp oldid 1100571997, wikipedia, wiki, book, books, library,

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