Aspidosiphon (Akrikos) albus Murina, 1967
This slender species is hookless and has a smooth white appearance. It can be found between 10 to 120 m depths; inside discarded mollusks shells, polychaete tubes, or associated with crustacean carapaces. The anal shield lacks grooves and usually has a dorsoventral median line of darker units easily identified.
(From Cutler 1994, Migotto a & Ditadi 1988, Stephen & Edmonds 1972)
External anatomy
Introvert is three to five times the trunk length, without hooks, but with many cylindrical papillae (6.5-8.0µm tall), arranged in irregular rings.
Apparently this species has no tentacles.
Trunk may be up to 45 mm long, slender with a smooth white appearance.
The anal shield is composed of fine grains with small furrows around the margin and lacks grooves. A dorsoventral median line of darker units is often present.
The caudal shield is conical; radial grooves are indistinct.
Internal anatomy
The longitudinal muscle layer of the trunk wall is continuous, except under the anal shield.
Intestine attached anteriorly and posteriorly by spindle muscle.
A small rectal caecum was observed in the specimens from Brazil (Migotto & Ditadi 1988).
Nephridia are 50-70% of the trunk length, attached to the body wall and open at the same level or posteriorly to the anus.
A pair of retractor muscles rises close to the caudal shield on the posterior end of the trunk.
This species has been found on the continental shelf (10-120 m) south from Cape Hatteras, northern Gulf of Mexico, Cuba and Brazil (Cutler, 1994).
This species usually occupies discarded shells of mollusks (such as gastropod and scaphopod shells), serpulid tubes or crustacean carapaces (Cutler, 1994).