Phascolosoma scolops

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 : 48

Phascolosoma scolops (Selenka & de Man, 1883)

( Fig. 3 E–F)

Material. Nha Trang Bay: Mung Island, 15 m depth, boring in bivalve shell Pinna sp., 1 specimen; Mot Island, 7 m depth, coral rubble, 7 specimens; Tre Island, intertidal, fouling community, 6 specimens.

Description. Trunk 18–25 mm long and 3–4 mm wide; pale or grey, slightly glossy with semitransparent body wall, with brown dome-shaped conical papillae increasing greatly in size anteriorly and posteriorly; pre-anal mammiform papillae reddish-brown, much larger dorsally. Introvert 1.5 X longer than trunk with wide pigmented bands more prominent dorsally. Yellow-brown tentacles with black pigments at the bases around the nuchal organ. Hooks with clear streak separated from the distinct triangle. Longitudinal musculature splits into 20–23 bands. Dorsal and ventral retractors originate 50–60% and 40% of trunk length from the posterior end, respectively. Gut with 12–15 loops; spindle muscle attached posteriorly. Nephridia about 50% of trunk length, about 2/3 attached to the body wall; nephridiopore and anus at the same level.

Discussion. Morphologically this species is similar to P. albolineatum . In contrast to P. s c o l o p s, the hooks of P. albolineatum bent at an obtuse angle which is a unique character to this species. The presence of a clear streak as well as a separated triangle in P. scolops is also seen in P. agassizii , while in the latter species the triangle is usually indistinct, and the steak not well visible in small specimens. These two species, in addition, may also be distinguished from each other by their trunk papillae structure and arrangement.

Phascolosoma scolops is a circumtropical and circumboreal species, widespread in the Pacific and Indian Ocean and also known from the Red Sea. In the West Pacific it has been reported from New Zealand to the Bering Sea. It can be usually found at intertidal and shallow depths in soft rocks, dead corals and coarse sand.

Figures

FIGURE 3. A – B. Phascolosoma arcuatum. A) lateral view, retracted introvert; B) hook. C – D. P. nigrescens. C) ventral view, introvert everted; D) hooks of P. nigrescens. E – F. P. s c o l o p s. E) lateral view, introvert everted; F) hook (black arrow – triangle of hook; black arrowhead-clear streak). G – I. P. stephensoni. G) lateral view, retracted introvert; H) hook; I) the row of hooks (black asterisk-basal warts). Scale bars: A, 10 mm; B, 50 µm; C, 10 mm; D, 50 µm; E, 5 mm; F, 50 µm; G, 5 mm; H – I, 50 µm.