Aspidosiphon (Paraspidosiphon) steenstrupii Diesing, 1859

Adrianov, Andrey V. & Maiorova, Anastassya S., 2012, Peanut worms of the phylum Sipuncula from the Nha Trang Bay (South China Sea) with a key to species, Zootaxa 3166, pp. 41-58 : 53-54

Aspidosiphon (Paraspidosiphon) steenstrupii Diesing, 1859

( Fig. 5 M–Q)

Material. Nha Trang Bay: Mot Island, coral rubble, 7 m depth, 2 specimens; Tre Island, coral rubble, 6 m depth, 8 specimens; Tre Island, fouling community, intertidal, 3 specimens; Mung Island, coral rubble, 12 m depth, 9 specimens; Diamond Bay, coral rubble, intertidal, 12 specimens.

Description. Trunk 5–15 mm long, 3–4 mm wide, whitish pale, with light brown pre-anal region, semitransparent; introvert subequal to trunk length. Anal shield ungrooved, consists of uniform-sized rectangular units, with calcium carbonate cap. Anal shield dark colored (brown or black) in specimens from gastropod shells and pale-yellow in specimens from dead corals. Caudal shield with radial and circular grooves. Tentacles of living specimens with brown pigments; compressed bidentate hooks 25–30 μm in height, arranged in rings, with tonguelike extension of internal clear streak; numerous pyramidal hooks 30 μm in height, scattered proximal to the rings of bidentate hooks; tubular papillae scattered between rings and pyramidal hooks. Longitudinal musculature in anastomizing bands and retractor muscles originate 20% of the trunk length from the caudal shield. Gut with 10–12 loops; spindle muscle attached posteriorly. Nephridia 2/3 of trunk length, unattached along their entire length.

Discussion. An ungrooved anal shield with calcium carbonate cap, rings of compressed bidentate hooks with tongue-like extension of the clear streak, scattered pyramidal hooks, and tubular papillae, all characters that separate Aspidosiphon (Paraspidosiphon) steenstrupii from all other representatives of the subgenus Aspidosiphon (Paraspidosiphon) .

This species is considered as a tropical and subtropical animal found in the Atlantic, Indian and Pacific Oceans, reported from Australia to Korea in the West Pacific, and from the coast of Vietnam and Hainan Island in the South China Sea. It inhabits coral rocks and mollusk shells in shallow water.

Figures

FIGURE 5. A – C. Aspidosiphon elegans. A) lateral view, introvert everted; B) bidentate hook; C) conical hook. D – H. A. gracilis. D) lateral view, introvert half everted; E) anal shield; F) caudal shield (white arrowhead - caudal shield.); G) hooks; H) the base of hooks (black asterisk - bifurcated posterior edge of hooks). I – J. A. muelleri. I) lateral view, introvert everted; J) hooks. K – L. A. laevis. K) lateral view, introvert everted; L) hooks. M-Q. A. steenstrupii. M) lateral view, introvert everted; N) close-up view of the introvert with calcareous anal shield (white arrow, calcareous cap on anal shield); O) bidentate hook; P) bidentate hooks & papillae; Q) pyramidal hooks. R-S. A. tenuis. R) lateral view, introvert everted; S) hook. Scale bars: A, 5 mm; B, 20 µm; C, 50 µm; D, 5 mm; E – F, 1 mm; G – H, 50 µm; I, 5 mm; J, 20 µm; K, 5 mm; L, 20 µm; M – N, 5 mm; O, 50 µm; P, 25 µm; Q, 50 µm; R, 5 mm; S, 50 µm.