Mystery Mollusc

Data: this is a strange animal. Doesal side has many dorsal scaly shells and it has a soft ventral body. It was collected from - 200m depth of southwester Taiwan.
Can you tell me what species it is? (seems like monoplacophoran? )

Send Ideas to: Tom




  • It looks similar to a species we have in Puget Sound (Washington State, U.S.A.)that's an echinoderm (holothurian). It's called Psolus chitonoides, (a sea cucumber "resembling a chiton"). The description states; "the shape of a short cucumber sliced lengthwise, for one side of it- the side with the tube feet-is almost perfectly flat. It clings tightly to rocks and is essentially sedentary. The upper surface is covered with overlapping calcareous plates, and the mouth is situated on this surface some distance from the anterior end. The color is orange; it's abundant in deeper water and its 5 cm in length." There is also another species I've never seen, listed as Psolidium bullatum which is smaller (3 cm) and pinkish-purple. I don't know if a similar species exists in Taiwan but it might be useful to ask an expert or look in marine biology texts. Our species is only found in dredged materials or by divers, not intertidally... Bert B

  • Psolus chitonoides should have tube feet on the ventral side!! the mystery animal looks like a flatworm! ...Constantine

  • There are some annelids with scales, but the organism is not obviously segmented. As far as I know, the scaled annelids have organic scales whereas the sea cucumbers would have calcareous (calcite) scales. This means the annelid scales would tend to dissolve somewhat in bleach, whereas echinoderm scales would dissolve readily in acid.
    How big is it?
    Any information on substrate? (was it on a rock, on another organism...)

    There are some bizzare parasites that lose most of the distinguishing features of their phylum as adults, so if it was living on something else, it could be a job for parasitology.

    Monoplacophorans are limpet-like, not like this.Some groups of sea cucumbers have lost the tube feet, but I don't know if any of them look like this... Dr. David C

  • Thanks to all who took a shot at the mystery "worm" from deep waters off Taiwan. There were no tube feet in evidence, so I eliminated an echinoderm. It was not segmented, so I eliminated an annelid. I finally went with a holothurian of the family Psolidae (thanks Bernd S). But I will include all answers so this individual can pick and choose for himself... Tom E.


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