Phascolosoma stephensoni (Stephen, 1942)

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 : 49

Phascolosoma stephensoni (Stephen, 1942)

( Fig. 3 G–I)

Material. Nha Trang Bay: Tre Island, 20 m depth, sand, boring in shell of Placuna sella , 1 specimen.

Description. Trunk 20 mm long, 4 mm wide; from light brown in anterior and middle trunk to dark brown posteriorly, with large conelike papillae concentrated at the anterior and posterior end. Introvert subequal to trunk length, with pigmented bands; hooks with smooth clear streak, clear triangular area, crescent and distinct secondary tooth on the concave side, with about six cuticular warts basally. Longitudinal musculature splits into 15–20 anastomizing bands; dorsal and ventral retractors originate 40% and 20% of trunk length from the posterior end, respectively. Gut with about 10 loops; spindle muscle attached posteriorly. Nephridia about 70–80% of trunk length with about 1/6 attached to the body wall; nephridiopores and anus at the same level.

Discussion. The internal structure of the hooks and the conical preanal and caudal papillae clearly distinguish P. stephensoni from other closely related species of the genus Phascolosoma .

This species is known from the Mediterranean, eastern Atlantic, Indian, and Pacific Oceans. It inhabits sandy bottoms and mollusk shells at shallow depths.

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.