Aculifera: Caudofoveata

Taxa on This Page

1. Caudofoveata

Introduction

The Caudofoveata are small, worm-like aberrant molluscs, ranging in length from 2 mm - 14 cm.. They construct burrows in soft marine sediments which they inhabit head downwards. They ingest sediment, or may be selective carnivores or scavengers. Many typical molluscan characteristics are either absent or reduced. There is no shell, no foot, and the mantle covers the entire body. Lacking a foot, they move by peristaltic contractions (like other primitive burrowing metazoa). They are dioecious (male and female reproductive organs in separate individuals). The posterior body cavity (believed to represent the mantle cavity) houses a pair of gills (ctenidia). The integument (skin) contains layers of embedded calcareous spicules. Most specimens have been collected by dredging, and relatively little is known about them. About 70 described living species of this class.

The Caudofoveata and Solenogasters are generally combined to form the class Aplacophora, although this practice is becoming discontinued as the differences between these two small primitive groups become known. For example, unlike Solenogasters, chaetoderms lack a pedal groove.

Like the Solenogasters, Caudofoveata are of great phylogenetic interest, and their precise evolutionary relationships are still unclear. Salvini-Plawen 1980 sees them as the sister group to all other molluscs, being little changed from the first "Scutopoda" (original burrowing forms). Bergström suggests that they may be surviving members of the Procoelomata, the ancestral sclerite-bearing early Cambrian metazoa. However, cladistic work by Haszprunar (Haszprunar 2000) indicates that Solenogasters are the most underived forms, with chaetoderms derived from them and higher (shell-bearing) molluscs next.

Caudofoveata

Synonym: Chaetodermomorpha

Phylogeny: Heloplacidae ::: *

Comments: Included under the probably polyphyletic Aplacophora. No foot, but they do have an oral shield and gills. Unlike the solenogastres, they have separate sexes. (Jack R. Holt)