Aspidosiphon ( Aspidosiphon )

Aspidosiphon ( Aspidosiphon) sp.

Figs 4–5 View Fig View Fig

Material examined

MEXICO • 1 spec.; Baja California, San Miguel Cove ; 28°09ʹ04ʺ N, 112°46ʹ06ʺ W; 6 May 1982; depth 30–35 m; Van Veen grab; Cortés stn 19, on board R/V El Puma; EMU-13432 GoogleMaps .

Description (EMU-13432)

Trunk 10 mm in length, width 1/10 as long as trunk length; smooth yellowish-brown skin; anterior and posterior ends darker ( Fig. 4A View Fig ). Mid trunk with two types of papillae: flat, oval, transversally elongated and small granules with a keratinized appearance, numerous and scattered, forming transverse or longitudinal lines along trunk. Introvert incomplete, anterior hooks 14 µm long laterally compressed and bidentate ( Fig. 5A–B View Fig ), arranged in rings, main tooth sharp; scattered posterior unidentate, pale hooks 16 µm long, with pyramidal base and conical tip ( Fig. 5C–D View Fig ), present towards anal shield; roll-type chitinized structure 16 µm long among scattered unidentate hooks ( Fig. 5 E–F View Fig ). Anal shield well-defined, formed by small, packed granules with ill-defined margins, scattered granules around shield ( Fig. 4C–D View Fig ). Caudal shield margin protruding, acorn-shaped, with 20 radial grooves ending in a rounded tip ( Fig. 4E View Fig ).

Longitudinal musculature in a continuous layer ( Fig. 4B View Fig ), in bands under anal shield. A pair of retractor muscles attached to body wall at posterior end of trunk; nephridiopores open anterior to anus.

Habitat

Subtidal ( 30–35 m); in muddy sand.

Distribution

Sea of Cortez, known only from stn 19 of the Cortés cruise, near Cabo San Miguel, Baja California.

Remarks

The unique specimen examined is incomplete, without a substantial portion of the introvert and part of the internal organs, i.e., no nephridia or intestine were present; however, what is observed on the specimen was sufficient to be able to identify it to subgenus.

Aspidosiphon ( A.) sp. is closely related to A. ( A.) misakiensis Ikeda, 1904 and A. ( A.) muelleri Diesing, 1852 ; however, there are some features which make A. ( A.) sp. different from any other species of the subgenus. Specifically, the presence of unidentate hooks with a pyramidal base and conical tip, the presence of the roll-type chitinized structure, which is not known for any of the species of the subgenus, and the presence of the two types of shields in A. ( A.) sp., an ungrooved anal shield with packed granules, and an acorn-shaped caudal shield. In A. misakiensis both shields consist of granules, as also in A. muelleri , where the anal shield is grooved.

Based on the latter, this specimen might represent a new species; however, it is necessary to obtain complete specimens to describe it formally.