Family ASPIDOSIPHONIDAE

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Family ASPIDOSIPHONIDAE

Introduction

Aspidosiphonids are small to medium-sized sipunculans with a trunk of 4-40 mm in length. They either have a hardened, horny, gold to dark brown anal shield or a white, calcareous knob or cap, both clearly marked off at the anterior region of the trunk. The introvert lies ventral to the shield, except in the genus Cloeosiphon in which it arises from the centre of the cap. In all but one species the introvert protrudes at an angle of 45-90º ventral to the main axis of the trunk. Tentacles are small and finger-like and arranged in a near ring around the nuchal organ. The longitudinal musculature is continuous in Aspidosiphon (Aspidosiphon) and in Cloeosiphon, but in bundles (with anastomoses) in Aspidosiphon (Paraspidosiphon) and Lithacrosiphon. Two nephridia are present and two retractor muscles which may fuse for much of their length. The spindle muscle is attached posteriorly. The type genus is Aspidosiphon of Diesing (1851).

The length of the introvert is variable, but is usually about as long as or twice that of the trunk. It is covered with numerous rings of closely packed, recurved hooks; spines may be present. Spines, when present, usually lie in a field posterior to that of the hooks. A hardened caudal shield is often present at the posterior extremity of Aspidosiphon. Both anal and caudal shields consist of small to large pigmented plates or platelets. The contractile vessel is without villi.

The family contains three genera, the diverse and speciose genus Aspidosiphon, and the two small genera Cloeosiphon and Lithacrosiphon. Aspidosiphon species are almost sedentary in habit and live in discarded shells, solitary corals, in crevices and under rocks and are found boring in coral and limestone reefs where they play a part in the physical disintegration of the environment. They are probably detritus and algal feeders.

Aspidosiphonids are inhabitants of tropical and temperate waters, especially the former. The affinities of Australian species are Indo-western Pacific. Several species of Aspidosiphon are known from the Great Barrier Reef and from the limestone and coral reefs of north-western Western Australia. Aspidosiphon muelleri is a common inhabitant of the solitary coral Heteropsammia michelini in Queensland. Edmonds (1980) listed 10 species of Aspidosiphon, one of Cloeosiphon and one of Lithacrosiphon from Australian waters.