Sipunculus (Sipunculus) polymyotus Fisher, 1947
This is a large species, with a trunk length up to 331 mm. The number of LMBs is the largest among Sipunculus, up to 55, and the brain has peculiar long digitate processes. When alive it has an orange iridescent color and may dig up to 80 cm into the sediment.
(From Fisher, 1947; Ditadi, 1982; and Cutler 1994)
External anatomy
Introvert shorter than the trunk (25-30% of the total trunk length), marked off from the trunk by its slender shape and by the scale like papillae covering its surface.
Trunk is cylindrical measuring up to 331 mm with a thick trunk wall. Trunk diameter/length ratio averages 1:10. The surface of the trunk is divided into a large number of small rectangles by the intersection of the longitudinal and circular muscles.
Glans region is not prominent.
Tentacular crown consists of two large ventral lobes and two smaller dorsal lobes, one of which may bifurcate giving the appearance of three, with the margin subdivided.
Internal anatomy
42- 55 longitudinal muscle bands (LMBs).
A pair of small free nephridia with irregular and knobby surface.
Brain has conspicuous digitate processes, appearing as large, leaflike flaps and long strings.
Two pairs of retractor muscles arise at the same level. The ventral pair originates in LMBs 1or 2 and spreads over six to seven bands, and the dorsal pair starts on LMBs 13-19 (usually 15 or 16) and spreads over five to six bands. The LMBs may split and double in the posterior end.
Spindle muscle is slender. Starting in front of the anus, it makes contact with the tip of the caecum and runs along the ascending intestine, attaching posteriorly to the intestinal wall.
Trunk length up to 331 mm (Ditadi, 1982).
This species is found in Fort Pierce, Florida, in the same area as S. nudus and Siphonosoma cumanenses (Kawauchi, personal observation).
This species is found in intertidal waters at the coast of São Paulo, Brazil, in intertidal zones to 30 m off southeastern United State (South Carolina, Florida, Panama City, Gulf of Mexico), Costa Rica (both sides), west cost of Panama, off Baja California, and one record from the Tasman Sea.
According Ditadi (1982) this species was collected from fine muddy and silty beaches, as well as from coarse and clean sand beaches in galleries up to 80 cm deep. Recently, S. polymyotus was collected in Fort Pierce Florida by digging about a meter deep in an intertidal sand flat exposed during low tide (Kawauchi, personal observation).