Phascolosoma nigrescens (Keferstein, 1865)

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 nigrescens (Keferstein, 1865)

( Fig. 3 C–D)

Material. Nha Trang Bay: Dung Island, 10 m depth, boring in bivalve shell Chama sp., 1 specimen; Tre Island, 6 m depth, coral rubble, 3 specimens; Tam Island, intertidal, fouling community, 1 specimen; Diamond Bay, intertidal, coral rubble, 7 specimens.

Description. Trunk 10–30 mm long and about 3–4 mm wide, light brown, brown or dark brown dome-shaped papillae, bigger towards the anterior and posterior end, respectively. Introvert pale, with or without pigmented bands, subequal to or 1.5 X longer than trunk length. Hooks with clear streak expanded in the middle and basal region of the hook. Longitudinal musculature splits into 20–25 occasionally anastomosing bands. Dorsal and ventral retractors originate at 65% and 30–40% of the trunk length from the posterior end, respectively. Gut with 15– 20 loops; spindle muscle is attached posteriorly. Nephridia are about 50% of trunk length with 30–50% of their length attached to the body wall.

Discussion. This species is well distinguished from other representatives of the genus Phascolosoma by the unique nature of the expanded streaks in the hooks.

Phascolosoma nigrescens is a circumtropical species widespread in the shallow waters of the Atlantic, Indian and Pacific Oceans. It can be found in the western Pacific from Australia to Tonkin Bay, and it is known to inhabit sand, dead coral, and mollusk shells in intertidal and shallow waters.

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.