Siphonosoma australe (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 : 44

Siphonosoma australe (Keferstein, 1865)

( Fig. 1 B–D)

Material. Nha Trang Bay: estuary of B river, muddy sand at depth 25–40 cm, 50 specimens; Tre Island, intertidal, 3 specimens; Nha Trang fish market, 10 specimens. Worms can be found by characteristic holes of their burrows in intertidal and shallow subtidal zones.

Description. Trunk up to 150 mm long and 12–15 mm wide; introvert about subequal in length to trunk with large, simple dark pointed hooks, 150–200 μm tall in about 50 rings. Tentacular apparatus subdivided in dorsal arc with 15–20 tentacles enclosing the nuchal organ; oral crown with 10–14 longitudinal festoons bearing up to 30 tentacles. Tentacles of living specimens with yellowish oral and greenish aboral surfaces, becoming whitish in preserved specimens. Body wall musculature often visible through the skin, with 15–16 longitudinal muscle bands. Dorsal retractors originate anterior to the ventral ones. Oesophagus with 2 fixing muscles, gut with 35–40 loops; spindle muscle with up to 3 branches. Contractile vessel with tiny villi, is contracted and indistinct in preserved specimens. Nephridia are free, about 40% of trunk length.

Discussion. The species is similar to S. rotumanun but can be easily separated by having characteristic hooks closely associated with large papillae. Another Indo-West Pacific species, S. cumanense , differs from S. australe by lacking introvert hooks and by the origin of dorsal and ventral retractor muscles at the same anterior-posterior level. S. funafuti , known from Southern Japan, Taiwan and South China Sea, differs by lacking hooks, and S. vastum , also widespread in the Indo-West Pacific, has multiple clusters of caecum on the rectum that are absent in S. australe .

Siphonosoma australe has a tropical and subtropical distribution and is found in shallow and intertidal waters, preferring sandy and muddy areas. It is known in the Indian Ocean from Indonesia to India and Madagascar. In the West Pacific it is reported from Australia and New Zealand to South China. Worms may be found by characteristic holes of their burrows in intertidal and shallow subtidal zones.

Figures

FIGURE 1. A. Sipunculus nudus, dorsal view, introvert everted. B – D. Siphonosoma australe. B) lateral view, introvert retracted; C) head with tentacular apparatus; D) hooks. Scale bars: A – B, 10 mm; C, 3 mm; D, 0.3 mm.