Aspidosiphon (Aspidosiphon) gracilis gracilis (Baird, 1868)
This species has a very weakly developed anal shield, composed of non-contiguous brown papillae surrounded by dark platelets, arranged in irregular longitudinal rows. The introvert arises from the trunk in an unusual angle for Aspidosiphon (60º). The distal hooks are compressed unidentate hooks followed by a proximal area of pyramidal ones. These worms have been collected in intertidal coral rubble in localities around the Pacific and Indian Ocean.
(From, Cutler 1994, Stephen & Edmonds, 1972).
External anatomy
Introvert 1.5 times the trunk length arising from the trunk at about a 60ºangle.
On the distal introvert only compressed unidentate hooks broader than tall (up to 40 µm) are arranged in rings, followed by a proximal area of pyramidal hooks.
The anal shield is weakly developed and composed of noncontiguous brown papillae surrounded by dark platelets arranged in ill-defined rows.
Trunk is slender and can be 15 times as long as thick.
The caudal shield is conical and has radial furrows.
Internal anatomy
The longitudinal muscle layer of the trunk wall is continuous except under the anal shield.
Intestine attached posteriorly by a strong spindle muscle.
Nephridia are as long as the trunk.
A pair of retractor muscles originates close to the posterior end of the trunk.
This species was found in Queensland, Indonesia, Philippines, Gulf of Aden, and the Andaman Island off India (Cutler, 1994).
This species lives in intertidal coral rubble (Cutler, 1994).