Solenogastres

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The Solenogastres (less often referred to as Neomeniomorpha), common name the solenogasters, are one class of small, worm-like, shell-less molluscs (Aplacophora), the other class being the Caudofoveata (Chaetodermomorpha). [1]

Some recent literature, and recent molecular evidence, indicates that the Aplacophora may be polyphyletic, and therefore these taxonomists divide Solenogastres and Caudofoveata into separate classes.[2]

Morphology

In contrast to all other molluscan classes, the Aplacophora have no shell, and are instead covered by aragonitic sclerites (calcareous spicules), which can be solid or hollow. These spicules can be arranged perpendicular to one another within the cuticle to form a skeleton, or can stick up to form a palisade, or can lie flat against the cuticle.[3]

80% of solenogaster species have a radula, while in others it is secondarily lost. The radula may bear one or more teeth per row; where there is more than one tooth, there is no central radular tooth.[3] The radula grows by dividing existing teeth in two, or by adding a new tooth at the centre of the radular row.[3] The salivary glands are very elaborate, and are an important character for taxonomy. Next to the mouth they have a unique sense organ, the vestibulum.

The solenogastres do not have true ctenidia, although their gill-like structures resemble them.[4]

Development

During development many Solenogastres are covered by a spiny scleritome comprising spines or scale-like plates; this has been likened to the halwaxiid scleritome.[5]

Sclerites of Epimenia start out solid before developing a hollow stem that subsequently solidifies.[6]

Ecology

Diet

Solenogasters feed on cnidaria and ctenophores, either sucking their bodily fluids or eating their tissue.[7] They do not use their radulae to rasp prey, as other molluscs do.[8]

Phylogeny

There is some uncertainty regarding the phylogenetic position of the solenogasters. Traditionally considered to be the most basal molluscan group and the sister group to the Caudofoveata, alternatives to both of these statements have been proposed on various lines of evidence.[5] Indeed, some molecular datasets plot Solenogastres as an outgroup to Mollusca.[9]

Families

Unassigned in Solenogastres
Synonyms
  • Superorder Aplotegmentaria (not monophyletic)
    • Myzomeniidae Thiele, 1894: synonym of Dondersiidae Simroth, 1893
  • Superorder Pachytegmentaria (not monophyletic)
    • Parameniidae Simroth, 1893: synonym of Pruvotinidae Heath, 1911 (invalid: type genus a junior homonym)
    • Pararrhopaliidae Salvini-Plawen, 1972: synonym of Pruvotinidae Heath, 1911
    • Perimeniidae Nierstrasz, 1908: synonym of Pruvotinidae Heath, 1911
    • Proneomenidae Mitchell, 1892: synonym of Proneomeniidae Mitchell, 1892
    • Pruvotiniidae Heath, 1911: synonym of Pruvotinidae Heath, 1911 (incorrect original spelling)
    • Solenopodidae Koren & Danielssen, 1877: synonym of Neomeniidae Ihering, 1876
    • Wireniidae Salvini-Plawen, 1978: synonym of Gymnomeniidae Odhner, 1920

References

  1. ^ MolluscaBase eds. (2021). MolluscaBase. Solenogastres. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=2094 on 2021-04-14
  2. ^ e.g. Todt, C.; Okusu, A.; Schander, C. & Schwabe, E. (2008). "Solenogastres, Caudofoveata and Polyplacophora.". In Ponder, W. & Lindberg D. (eds.). Phylogeny and Evolution of the Mollusca. University of California Press. ISBN 978-0-520-25092-5.
  3. ^ a b c Scheltema, A. H. (1999). "Two solenogaster molluscs, Ocheyoherpia trachia n.sp. From Macquarie Island and Tegulaherpia tasmanica Salvini-Plawen from Bass Strait (Aplacophora: Neomeniomorpha)". Records of the Australian Museum. 51: 23–31. doi:10.3853/j.0067-1975.51.1999.1266.
  4. ^ Wilbur, Karl M.; Trueman, E.R.; Clarke, M.R., eds. (1985), "2. Early evolution and the Primitive Groups", The Mollusca, 10. Evolution, New York: Academic Press, ISBN 0-12-728702-7
  5. ^ a b Todt, C.; Wanninger, A. (2010). "Of tests, trochs, shells, and spicules: Development of the basal mollusk Wirenia argentea (Solenogastres) and its bearing on the evolution of trochozoan larval key features". Frontiers in Zoology. 7 (1): 6. doi:10.1186/1742-9994-7-6. PMC 2828982. PMID 20181015.
  6. ^ Okusu, A. (2002). "Embryogenesis and development of Epimenia babai (Mollusca: Neomeniomorpha)". The Biological Bulletin. 203 (1): 87–103. doi:10.2307/1543461. JSTOR 1543461. PMID 12200259.
  7. ^ Guralnick, R.; Smith, K. (1999). "Historical and biomechanical analysis of integration and dissociation in molluscan feeding, with special emphasis on the true limpets (Patellogastropoda: Gastropoda)". Journal of Morphology. 241 (2): 175–195. doi:10.1002/(SICI)1097-4687(199908)241:2<175::AID-JMOR7>3.0.CO;2-0. PMID 10420163.
  8. ^ Scheltema, A. H.; Jebb, M. (1994). "Natural history of a solenogaster mollusc from Papua New Guinea,Epimenia australis(Thiele) (Aplacophora: Neomeniomorpha)". Journal of Natural History. 28 (6): 1297. doi:10.1080/00222939400770661.
  9. ^ Wilson, N.; Rouse, G.; Giribet, G. (2010). "Assessing the molluscan hypothesis Serialia (Monoplacophora+Polyplacophora) using novel molecular data". Molecular Phylogenetics & Evolution. 54 (1): 187–193. doi:10.1016/j.ympev.2009.07.028. PMID 19647088.
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Solenogastres: Brief Summary

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The Solenogastres (less often referred to as Neomeniomorpha), common name the solenogasters, are one class of small, worm-like, shell-less molluscs (Aplacophora), the other class being the Caudofoveata (Chaetodermomorpha).

Some recent literature, and recent molecular evidence, indicates that the Aplacophora may be polyphyletic, and therefore these taxonomists divide Solenogastres and Caudofoveata into separate classes.

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Classification

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Supraspecific classification used herein is essentially based on Salvini-Plawen (1978), also summarized in García–Álvarez & Salvini-Plawen (2007).
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Classification

provided by World Register of Marine Species
There is a debate over whether Solenogastres should be a subclass of a Class Aplacophora or a separate class. The phylogenetic relationships of aplacophoran molluscs are not unambiguously resolved although the data at hand (see Haszprunar 2000: American Malacological Bulletin 15, 115-130, and Glaubrecht, Maitas & Salvini-Plawen, 2005: Mitteilungen aus der Museum für Naturkunde in Berlin – Zoologische Reihe 81, 145-166) would support a relationship like Solenogastres(Caudofoveata(Polyplacophora(Conchifera)))) making Aplacophora paraphyletic. For this reason, contra the Aculiferan hypothesis of Scheltema (1993: Biological Bulletin 184, 57-78) and in agreement with the European school of Salvini-Plawen, Solenogastres and caudofoveata are given full class status.
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Classification

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Originally proposed as a group of "worms" of uncertain affinity, to include both Neomenia and Chaetoderma, which are respectively representative of the Solenogastres (in the modern acception) anc Caudofoveata. At that time the group was not considered as related to the Mollusca
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