Aspidosiphon (Aspidosiphon) muelleri Diesing, 1851

General description:

This species is the most widespread, eurytopic and polymorphic Aspidosiphon, with a long list of synonyms and morphology difficult to define. The anal shield is composed of small units arranged in different sized plates and divided in 3 sections: dorsally the plates are separated by longitudinal furrows, and in the midsection by transverse furrows. Ventrally there are raised wart like or cone shaped units. Specimens may have only compressed unidentate hooks on the introvert, only compressed bidentates or both. The trunk shape varies according to the form of the shelter where the worm is found. However the most common shelter for A. muelleri is discarded gastropod shell.

Morphology:

(From Cutler & Cutler 1989, Cutler 1994)

Morphology

Introvert 1 to 3 times the trunk length

Tentacle crown composed of 6 to 12 small tentacles around the nuchal organ.

The hook morphology in this species is controversial and has been discussed by Southern (1913), Stephen & Edmonds (1972) and Cutler & Cutler (1989). The latter authors analyzed different populations and concluded that each specimen has the ability to produce only compressed unidentate, only bidentate or both kinds of hooks. Pyramidal hooks are found behind the area with the compressed hooks on the most proximal area of the introvert. At the posterior base of the compressed hooks are comb like structures.

The anal shield can be tan to black and is composed of small units arranged into different sized plates partially separated by longitudinal furrows dorsally, and by transverse furrows in the midsection. On the ventral region of the anal shield there are raised wart like or cone shaped units.

Trunk is usually 10 to 30 mm long and the shape will vary according to the form of the shelter where they are found.

Internal anatomy

The longitudinal muscle layer of the trunk wall is continuous except under the anal shield.

Rectal caecum is absent.

Nephridia are about 25 to 100 % of the trunk length and open at the level of or slightly posterior to the anus.

A pair of retractor muscles originates near the caudal shield (at 95 to 100% of the trunk length).

Size:

Specimens with trunk up to 80 mm long have been reported (Cutler, 1994), but trunk length is commonly 10 – 30 mm.

Associations:

(From Yonge, 1975)

In the Indo Pacific region Aspidosiphon muelleri is found in commensalism with a solitary coral from the genera Heteropsamia and Heterocyathus. A planula larvae of the solitary coral settle on the outside of a discarded gastropod shell containing a juvenile of A. muelleri, and eventually the coral overgrows and absorb the shell’s material into its own tissue and the sipunculan continues to live in a coiled space within the coral. There is a opening on the basal plate of the coral from where the worm extend the introvert to feed, plus a series of smaller openings on the lateral side of the coral for irrigation. The sipuncula extending the introvert trough the opening can moves the coral and maintains it in an upright position. The coral benefits by being move if the local condition deteriorates and the worm has the shelter benefit from the coral.

Distribution:

(From Cutler, 1994)

This is the most widespread Aspidosiphon species and has been found from Norway through the British Isles, the Azores, the Canary Islands, Adriatic, Aegean, Red Seas, Gulf of Aden, East Africa, Madagascar, South Africa, Sri Lanka, Japan, Thailand, Vietnan, Indonesia, Australia, New Guine, Kermadec Island. It is found in most of the Pacific Ocean, one record from Juan Fernadez Island off Chile (33º S) and one from southern Brazil (34º S).

Habitat:

(From Cutler, 1994)

This species is more often found living in discarded gastropod shells in shelf depth from 5 to 400 m. However there are several records at depths, such as at 1000 m and few as deep as 2900 m.

Sipuncula

Sipuncula

Aspidosiphon (Aspidosiphon) muelleri Diesing, 1851

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