Aplacophoran mollusks-Still obscure and difficult?

摘要

In numbers, the aplacophoran mollusks are of subordinate importance amongst the Mollusca and they remain a somewhat obscure group as compared to gastropods, bivalves, or even chitons. The ongoing confusion when it comes to naming, categorizing, and classifying what is known as either the class Aplacophora with subclasses Chaetodermomorpha and Neomeniomorpha, or the two classes Solenogastres and Caudofoveata, is not helpful in this matter, either. Nevertheless the last decade has brought a number of important results when it comes to aplacophoran biology, morphology, taxonomy, and currently also aplacophoran phylogeny. These results point to a sistergroup relationship between Solenogastres and Caudofoveata, but also show that there are a number of crucial differences that support a classification into two separate classes. Here, the current status of aplacophoran research is outlined and important open questions are discussed as focus areas for future studies.