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Solenogastres

Class of molluscs From Wikipedia, the free encyclopedia

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

Quick Facts Scientific classification, Orders ...

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

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Morphology

In contrast to many other mollusc classes, aplacophorans 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, 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 center of the radular row.[3] The salivary glands are very elaborate, and are an important characteristic for taxonomy. Next to the mouth they have a unique sense organ, the vestibulum.

Solenogastres do not have true ctenidia, though their gill-like structures may resemble them.[4]

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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]

Solenogastres can be found in a diverse range of habitats across the world, from the coast to the deep ocean.[7]

Ecology

Diet

Solenogastres feed on cnidaria and ctenophores, either sucking their bodily fluids or eating their tissue.[8] They do not use their radulae to rasp prey, as some other molluscs do.[9]

Phylogeny

There is some uncertainty regarding the phylogenetic position of the Solenogastres. 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.[5] Some molecular datasets plot Solenogastres as an outgroup to Mollusca.[10] However, there are cryptic species which are hard to delineate due to there being a lack of multiple morphological characteristics.[11]


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Families

Unassigned in Solenogastres
  • Pholidoherpia Salvini-Plawen, 1978
  • Rhabdoherpia Salvini-Plawen, 1978
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
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Images

Thumb
Preserved specimen of Epimenia verrucosa
Thumb
Photograph of Rhopalomenia aglaopheniae, observed off the coast of Scotland

References

Further reading

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