Siphonosoma cumanense (Keferstein, 1897)

Vargas, Rita & Kawauchi, Gisele Y., 2010, Sipunculans and Echiurans of Isla del Coco (Cocos Island), Costa Rica, Zootaxa 2557, pp. 60-68 : 61-62

Siphonosoma cumanense (Keferstein, 1897)

Material examined. Bahía Chatham, 12 October 2007, one specimen, 13 mm.

Description. The longitudinal muscle layer was divided into 21 distinct, non-anastomosing muscle bands; dorsal and ventral retractor muscles originate at the same position along the body length. The single specimen was broken off posteriorly so possible structures such as fusiform bodies or a fixator muscle could not be seen. Introvert Tentacles were digitate and unbranching; brain much longer than wide, processes absent. Numerous short, reddish-brown digitate contractile vessel villi present; remainder of intestine poorly preserved; rectum long, muscular, with proximal rectal caecum. Two short nephridia present.

Habitat. subtidal sandy bottom, 29.9 m.

Remarks. According to Cutler (1994) the line of demarcation between the trunk and the retractable introvert occurs in the Sipuncula at the level of the nephridiopores (which is usually also the level of the anus). In Siphonosoma cumanense the introvert is wider posteriorly and includes highly anastomosing longitudinal muscle bands while anteriorly the introvert narrows and separate longitudinal muscle bands are absent. The clearly separated longitudinal muscle bands of the trunk region have no such anastomoses between bands. A similar situation was also noted in additional specimens of Siphonosoma cumanense collected from Florida and the Barbados in the MCZ collections. Cutler (1994) revised the genus description of Siphonosoma to include the presence of anastomosing longitudinal muscle bands as a character of the genus and used this character to distinguish this genus from the morphologically similar Sipunculus . At least in S. cumanenese the region of anastomosing longitudinal muscle bundles is present only in a limited region of the body.

Distribution. Siphonosoma cumanense has been previously reported from tropical and subtropical regions of the Western Atlantic, Western Pacific and Indian Oceans as well as the Red Sea ( Cutler 1994). This is the first record for this species from the Eastern Pacific.