Aspidosiphon (Paraspidosiphon) tenuis Sluiter, 1886

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 : 54

Aspidosiphon (Paraspidosiphon) tenuis Sluiter, 1886

( Fig. 5 R–S)

Material. NhaTrang Bay: Mot Island, coral rubble, 7 m depth, 3 specimens; Tre Island, coral rubble, 6 m depth, 6 specimens; Tre Island, intertidal, fouling comunity, 5 specimens; Diamond Bay, coral rubble, intertidal, 20 specimens.

Description. Trunk 5–15 mm long, 2–3 mm wide, pale or light brown, semitransparent; introvert 1.5– 2 X trunk length. Anal shield green or brown-green, smooth and glossy, sometimes saddle-shaped or concave, composed of small dark units, with short marginal grooves; caudal shield brown-green, with radial grooves. Tentacles with white pigments; bidentate hooks 30 μm in height, arranged in rings on the distal introvert; unidentate hooks scattered on the proximal introvert. Pyramidal hooks absent. Longitudinal musculature splits into 23–25 anastomozing bands; retractor muscles originate 10% of trunk length from the caudal shield. Gut with 10–15 loops. Nephridia are about 80–90% of trunk length, unattached.

Discussion. This species differs from other representatives of the subgenus Aspidosiphon (Paraspidosiphon) by the anal shield structure, the presence of both bidentate and unidentate hooks, and the absence of pyramidal hooks.

This is a tropical Indo-West Pacific species known from Australia to Taiwan. It inhabits coral rocks and 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.