Aplacophora is a small enigmatic group of worm-like molluscs covered by sclerites. The general morphology of the posterior end, including the gonopericardial system, in many species is well studied using light microscopy. However, knowledge of the ultrastructure

Chaetoderma nitidulum Lovén, 1844 is a common species of caudofoveate (chaetodermomorph) with a wide distribution range in the northeastern Atlantic Ocean. It was the first species of aplacophoran mollusc to be described, but its species identity has

The worm-shaped, shell-less aplacophoran molluscs Caudofoveata and Solenogastres have recently received attention as part of the clade Aculifera, but relationships within these two lineages are still largely unknown. Here, we use complete mitochondrial