Life in the mud: Observations in aquariums and functional morphology of the hydrostatic skeleton of Chaetoderma nitidulum (Mollusca, Caudofoveata)

Caudofoveata is a clade of worm-like mollusks that lead a burrowing lifestyle in soft marine sediments. There are only a few references to peristaltic movement in members of Caudofoveata. The movement of individuals of Chaetoderma nitidulum collected from the White Sea and set into a transparent gelatin substrate was described by direct observation. The morphology and ultrastructure of the musculature and circulatory system were described in detail using morphological methods (light and electron microscopy, and 3D reconstruction from a series of semithin sections). Based on the analysis of the movement and morphology of the body wall and body cavities, the main phases of movement were distinguished. The peristaltic movement observed in C. nitidulum is superficially similar to the peristalsis phases described for Annelida and completely coincides with the classical description of direct peristalsis.