Family CHAETODERMATIDAE

Chaetodermatidae

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Family CHAETODERMATIDAE

Introduction

The Chaetodermatidae is a cosmopolitan family of Chaetodermomorpha comprising five genera and somewhat more than 70 species. Species of Chaetodermatidae live primarily on continental shelves and upper continental slopes. Falcidens poias Scheltema, which was collected at a depth of 3 m from Rottnest Island, WA, is an unusual littoral exception (Scheltema 1995). Besides F. poias, the family is represented in Australia by one species each in Falcidens Salvini-Plawen and Lepoderma Salvini-Plawen (raised herein from subgeneric rank to genus) in Bass Strait and one species each in Chaetoderma Lovén and Falcidens on the continental slope off the south-eastern coast (Scheltema 1989). The two other genera, Furcillidens Scheltema and Caudofoveatus Ivanov, have not been collected from Australian waters.

Chaetodermatidae species are usually more than 5 mm long and may be quite large, 3 cm or more; Chaetoderma usitatum Scheltema from off southeast Australia is one such robust species. Spicules are flat and leaf-like or somewhat bent, usually with longitudinal sculpturing. The genus Lepoderma, however, is defined by spicules bearing crossed diagonal ridges. Spicules may vary in morphology from anterior to posterior, as in C. usitatum, or they may have a similar form throughout, as in Lepoderma and Australian species of Falcidens. Body regions are more or less distinct, with an anterior constriction separating a neck region from the trunk; the trunk has an anterior region containing the stomach and usually a broader posterior region containing the gonad and digestive gland. The form of the radula is diagnostic, consisting of two denticles at the distal end of a long, cone-shaped cuticular piece.

Chaetodermatids, as far as is known, are carnivores, preying on foraminiferans and other small organisms. They move by hydrostatic action, burrowing slowly through the mud.

Like other Chaetodermomorpha, Chaetodermatidae species are dioecious. Chaetoderma has a unique and unusual ectaquasperm with two flagella initially and an acrosome at the tip of a long, non-nuclear tube (Buckland-Nicks & Chia 1989).

The nominate species, Chaetoderma nitidulum Lovén from the south-west coast of Sweden, is not known from a holotype or syntype specimen. Recent collecting from that area has uncovered six or seven species, all very similar in appearance and in two genera (Ivanov & Scheltema 2000); it remains to be determined which species is C. nitidulum. The synonymies herein reflect the present published decisions.