Solenogastres

Solenogastres are small worm-like mollusks found exclusively in marine habitats. They can be found all over the globe from shallow reefs to deep Antarctic waters. They range in size from large 30cm species to tiny ones that live between sand grands and are less than half a millimeter long. Solenogastres do not have a shell common among mollusks and are instead covered in calcium carbonate scales and spicules called sclerites.

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Taxonomy

Solenogasters and Caudofoveates together form the group called Aplacophorans. Aplacophorans and polyplacophorans form the clade called Aculifera that is sister to all other mollusks (conchifera). Solenogastres is currently divided into four orders including Pholidoskepia, Neomeniamorpha, Sterrofustia, and Cavibelonia. 

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Pholidoskepia

Scaly sclerites

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Neomeniamorpha

Stout body shape with scale, needle, grooved, or harpoon shaped sclerites. 

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Sterrofustia

Thick cuticle with hollow needle, paddle, or hook shaped sclerites. 

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Cavibelonia

Thick cuticle with hollow needle shaped sclerites. 

Solenogastres Orders

Anatomy

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The sclerites of solenogasters are made of aragonite, a hard form of calcium carbonate. These sclerites can be found in a wide range of types including ones that look like scales, leaves, spines, hooks, and troughs. Some solenogasters will even have multiple different types of sclerites covering their bodies. These sclerites will often give solenogasters a shiny appearance. 

The body of solenogasters have a uniform worm-like appearance. They have a narrow foot that runs along the bottom of the body. This foot is lined with pedal glands that secrete mucous to aid in movement. Solenogasters lack traditional gills and respire folds in the mantle cavity.

Ecology

Solenogasters are carnivores feeding on cnidarians, mollusks, and annelids among other possible prey taxa. They can be found wrapped around the branches of soft corals which they prey on.

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Citations

García-Álvarez, Ó., & Salvini-Plawen, L. (2007). Species and diagnosis of the Families and Genera of Solenogastres (Mollusca). Iberus, 25(2), 73–143. https://doi.org/10.5281/zenodo.4533262

Kocot, K. M., Poustka, A. J., Stöger, I., Halanych, K. M., & Schrödl, M. (2020). New data from Monoplacophora and a carefully-curated dataset resolve molluscan relationships. Scientific Reports, 10(1), 1–8. https://doi.org/10.1038/s41598-019-56728-w

Ponder, W. F., Lindberg, D. R., & Ponder, J. M. (2020). Polyplacophora, Monoplacophora, and Aplacophorans. In Biology and evolution of the mollusca (Vol. 2, pp. 67-107). Boca Raton: Taylor & Francis.