Phascolion (Isomya) convestitum Sluiter, 1902

General description:

In this species the anus is at the anterior end of the trunk and holdfast papillae are usually variable. Hooks are broad-based, recurved and pointed. Dorsal retractor muscle is slightly larger than the ventral muscle.

Look alikes:

According to Cutler and Cutler (1985) P. convestitum is similar to P. tuberculosum in many ways. They suggested that the former species may only deserve subspecific rank, but they did not propose any change for P. convestitum.

Morphology:

(From Cutler and Cutler, 1985; Cutler, 1994)

External anatomy

Hooks with broad base, recurved and pointed (50-100 µm tall).

Holdfast papillae from large and bulbous to small and compact. Some have granular material around the border as a distinct unit, others are without hardened material, others have a smooth and slightly darker border.

Tentacular crown consists of 20-25 normal tentacles.

Anus at the anterior end of the trunk.

Internal anatomy

Dorsal retractor slightly larger than ventral .

Dorsal retractor with single origin.

Ventral muscle with two origins, which straddle the ventral nerve cord near its posterior end.

Esophagus may be connected to the dorsal retractor muscle.

Intestine in loops with few loose coils.

Short and strong fixing muscle at the posterior end of the coil, attaching it to the trunk wall between the roots of the ventral retractor muscle (this is not a spindle muscle).

Distribution:

Mediterranean, Red Sea, Gulf of Aden and Indonesia (Cutler, 1994).

Habitat:

From 25-275 m (Cutler, 1994).

Sipuncula

Sipuncula

Phascolion (Isomya) convestitum Sluiter, 1902

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