Aspidosiphon (Akrikos) venabulum Selenka & Bülow, 1883
This is a hookless species, which has an ungrooved anal shield that resembles the anterior end of certain Phascolion species with large anterior papillae.
Type: Museum für Naturkunde, Humboldt-Universtät, Berlin, MNHU 644.
(From Cutler 1994, Stephen & Edmonds 1972)
Introvert at least 5 times the trunk length, and hooks are completely absent.
Trunk up to 30 mm long.
The anal shield is composed of dark, pointed, conical units more widely scattered than in many species and completely lacks grooves. It can resemble the anterior end of some Phascolion species that have large papillae on the anterior end of the trunk.
The caudal shield does not have the pointed units, but is composed of small closely arranged plates.
The trunk wall has a continuous longitudinal muscles layer except under the anal shield.
Intestine attached anteriorly and posteriorly by spindle muscle.
Nephridia are 60 to 95% of the trunk length and are attached to the trunk wall for two thirds of their length.
A pair of retractor muscles extends to the posterior end of the trunk, arising from the caudal shield.
Ecology and Distribution
This species has been found mainly in Africa, however, there is one report from southern Madagascar, including specimens at shelf depth from 10 to 55 m, the intertidal zone and 960 m (Cutler 1994).