Abstracto
- The sipunculan fauna of Isla del Coco was found to be quite diverse with eleven species reported. Several of the sipunculan species, as well as the echiuran Thalassema steinbecki, have been encountered previously from Pacific Costa Rica. More surprising is the occurrence of several species of sipunculans not previously known from the eastern Pacific region such as Siphonosoma cumanense, Phascolosoma scolops, Aspidosiphon gosnoldi, A. misakiensis, and A. (Paraspidosiphon) laevis. Possible larval sources for those species previously unknown from this region are discussed. The identity of specimens previously identified as Phascolosoma perlucens from Pacific Costa Rica are in question and are referred to as P. sp. The presence of anastomosing longitudinal muscle bands as being characteristic of the genus Siphonosoma is discussed.