﻿376 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



and ventral to the brain. The esophageal connectives do not surround 

 the attachments of the retractor muscles to the head, as in most 

 sipunculids, but lie behind and beneath these attachments" (Gerould, 

 1913, p. 427). The brain is conspicuous. On its front is a con- 

 spicuous cerebral organ or frons, sometimes elaborately lobed (Fisher, 

 1947, pi. 10, fig. 2; pi. 11, fig. 3). The ventral nerve cord is not 

 attached anteriorly by a mesentery to the wall of the introvert, as in 

 SiphonosoTua. It is supported on each side by a strong paraneural 

 muscle originating from the first, or first and second, muscle bundles 

 just posterior to beginning of introvert. 



Remarks. — Plate 18, figure 1, shows the accessory intestinal spiral 

 A dissociated from the regular spiral B. This is easily accomplished 

 by clipping the fixing muscles that hold it in place. I have figured 

 (Fisher, 1947, pis. 10, 11) this extra spiral in situ in Sipuvculus 

 polymyotus and S. galapagensis, where the bends X and Y are indicated. 

 The details of the fixing muscles are so different in these two species 

 as to suggest that they may be of value in classification. 



The accessory spiral is not present in Xenosiphon or in Siphonosoma. 



SIPUNCULUS NUDUS Linnaeus 



Plate 18 

 Sipunculus nudus Linnaeus, 1766, p. 1,078. 



Remarks. — This is perhaps the best known and certainly one of the 

 most widely distributed species of sipunculids — a truly eurythermal 

 type. On the west coast of America it occurs from Monterey Bay, 

 Calif., to Panama. It is found on the coast of Brazil, in the West 

 Indies, and north to Beaufort, N. C. In Europe it inhabits the 

 North Sea, English Channel, and the Mediterranean and Adriatic 

 Seas. It is reported from the Red Sea, Indian Ocean, East Indies, 

 China, Japan, along the western part of the Pacific (Yap, Loyalty 

 Islands), and South Australia.^ 



The specimens recorded below have 30 to 33 muscle bundles. The 

 ventral retractor muscles arise from longitudinal muscles 1-7, 1-6, 

 or 2-5 (Ensenada) ; the dorsal retractors arise from 9-15, 10-14, 10-15, 

 11-16. A large specimen from southern California is 190 mm. long, 

 but others are considerably smaller, circa 130 mm. The longest 

 specimen is 290 mm. and was washed ashore at Pacific Grove, Calif., 

 during a heavy surf. 



The species has not been found at Monterey Bay in intertidal 

 situations, even at Elkhorn Slough, which has been rather thoroughly 

 explored by Prof. G. E. MacGinitie and others; but it occurs in sub- 

 tidal situations, since many were washed ashore during a period of 

 spring tides and heavy surf. It seems probable that Newport Bay 



' A specimen sent me by S. J. Edmonds from Port Willunga, south of Adelaide, South Australia, Is super- 

 ficially like S. nudus but belongs to another, probably new, species. 



