Aspidosiphon (Aspidosiphon)

Gómez-Vásquez, Julio D., 2024, New records and five new species of sipunculans (Sipuncula) from the central and northwestern Mexican Pacific, European Journal of Taxonomy 925, pp. 179-219 : 188-190

Aspidosiphon (Aspidosiphon) sp.

Figs 4–5

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 .

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 ). 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 ), arranged in rings, main tooth sharp; scattered posterior unidentate, pale hooks 16 µm long, with pyramidal base and conical tip ( Fig. 5C–D ), present towards anal shield; roll-type chitinized structure 16 µm long among scattered unidentate hooks ( Fig. 5 E–F ). Anal shield well-defined, formed by small, packed granules with ill-defined margins, scattered granules around shield ( Fig. 4C–D ). Caudal shield margin protruding, acorn-shaped, with 20 radial grooves ending in a rounded tip ( Fig. 4E ).

Longitudinal musculature in a continuous layer ( Fig. 4B ), 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.

Figures

Fig. 4. Aspidosiphon (Aspidosiphon) sp. (EMU-13432). A. Lateral overview, introvert incomplete. B. Internal anatomy. C. Anal shield, dorsal view. D. Anal shield, lateral view. E. Caudal shield. Abbreviations: see Material and methods. Scale bars: A–B = 3 mm; C–E = 0.5 mm.

Fig. 5. Aspidosiphon (Aspidosiphon) sp. (EMU-13432). A–B. Bidentate laterally compressed hook. C–D. Unidentate hook with pyramidal base and cylindrical tip. E–F. Roll-type hook. Scale bars: A, C, E = 10 µm.