Aplacophora
The naked mollusks
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# of Described Species: 320 First Appearance: Holocene Habitats: Marine, mostly deep-sea Shapes: Worm-like Feeding Types: Carnivorous |
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# of Described Species: 320 First Appearance: Holocene Habitats: Marine, mostly deep-sea Shapes: Worm-like Feeding Types: Carnivorous |
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Aplacophora is a relatively small group of mollusks that are characterized by their lack of shells
and worm-like appearance. Instead of a shell, their mantle secretes tiny calcareous spicules
which give them a beautiful shine. There are only about 320 species of these exclusively
marine mollusks.
There is a good chance that Aplacophora is a paraphyletic group. The two groups of aplacophorans are the footless Caudofoveata (also known as Chaetodermomorpha) and the Solenogastres (or Neomeniomorpha). |
Unfortunately this group is understudied and thus species-level diversity is severely underestimated
in this poorly collected group. The knowledge base that does exist is remarkable when one considers
that this is primarily a deep-water taxon. However, molecular phylogenetic studies of this taxon
are lacking still few and its placement on the molluscan tree problematic.
Fossils that are certainly aplacophorans have not been found. Partly due to spicules which are not interconnected and the difficulty of fossilizing soft body parts, it has been difficult to determine whether or not some problematic fossils belong to Aplacophora or not. Given their position on the phylogenetic tree of mollusks, though, it is likely aplacophorans have been around since the Cambrian. |
