Siphonosoma cf. vastum (Selenka, de Man & Bulow, 1883)

Silva-Morales, Itzahí & Gómez-Vásquez, Julio D., 2021, First records and two new species of sipunculans (Sipuncula) from the Southern Mexican Pacific, European Journal of Taxonomy 740 (1), pp. 77-117 : 83-86

publication ID 10.5852/ejt.2021.740.1283

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Siphonosoma cf. vastum


Siphonosoma cf. vastum View in CoL (Selenka & Bülow in Selenka, 1883)

Fig. 4 View Fig

Type locality of nominal species

Jaluit, Marshall Islands ( Selenka 1883: 103–104, pl. 12, fig. 171, pl. 13, fig. 179).

Material examined

MEXICO • 1; Oaxaca, San Agustín Bay; 15°41′21″ N, 96°14′11″ W; 24 Oct. 2004; SCJ leg.; depth 3 m, under rock in sand; UMAR-SIPU 105 GoogleMaps .


Trunk 150 mm in length in preserved specimens ( Fig. 4A View Fig ), 300 mm in living specimens. More than 60 filiform tentacles. Introvert with dispersed orange papillae ( Fig. 4C View Fig ) and reddish region with rectangular papillae ( Fig. 4D View Fig ). Trunk with light brown body wall ( Fig. 4E View Fig ). More than 100 rings of claw-shaped hooks ( Fig. 4G View Fig ). Twenty-six anastomosing longitudinal muscle bands ( Fig. 4H View Fig ). Two long, tiny and dark brown free nephridia occupying 40% of trunk, about 35% attached to body wall. Two pairs of retractor muscles; dorsal pair attached to five bands starting from second band after ventral nerve cord, ventral pair attached to nine bands ( Fig. 4B View Fig ). Multiple rectal caeca covering 90% of rectum ( Fig. 4F View Fig ). Spindle muscle attached posteriorly. Nephridiopore almost at same level of anus.


The species is similar to Siphonosoma australe australe ( Keferstein, 1865) , described from Sydney, Australia, and to S. vastum (Selenka & Bülow in Selenka, 1883), described from Jaluit, Marshall Islands ( Table 3 View Table 3 ). Siphonosoma cf. vastum differs from S. australe australe in that the former species has multiple rectal caeca in 90% of the rectum, which are absent in the latter. According to Cutler et al. (1992), S. vastum is able to disperse across the entire Tropical Pacific Ocean. However, the nominal species is different from S. cf. vastum from Mexico in many diagnostic characters, mainly the coverage of the multiple rectal caeca in the rectum and the attachment of the muscles in the body wall ( Table 2 View Table 2 ). This species is a possibly a new species; however, more specimens are needed to describe it.


Subtidal (3 m); in sand.


San Agustín Bay, Oaxaca, Mexico.

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