POLYCHAETE WORMS, PART 1 315 



ment is not known but it is probably entirely pelagic. Advanced 

 ciKated larvae have been found in the plankton in Swedish and 

 Danish waters in March to July, most numerous in April and May, 

 when they may be the dominating polychaete larvae in the plankton 

 (Hannerz, 195G; Thorson, 194G, as spionid larva D); the larvae are 

 predominantly planktotrophic. 



Hannerz followed the development of the advanced planktonic 

 larvae to the metamorphosed young benthonic stage, when they built 

 a tube of mud particles and a secretion (thoracic region with 9 bi- 

 ramous segments; abdominal region with 13 uniramous segments, 

 with 4 anal cutI; they swim in doubled up position, folding at the 

 transitional region). The larvae are characterized by the outspread 

 shield or "umbrella" formed by the coalesced prostomium and peri- 

 stomium. The tentacular palps are formed relatively late, the right 

 one characteristically longer than the left one. The larval setae of the 

 fh'st setiger are especially long. 



Material examined. — Type slides of Thaumastoma singulare 

 Webster and Benedict from Cape Cod, Massachusetts; types of 

 Disoma franciscanum Hartman from central California. Single small 

 specimen from Cape Cod Bay, 21 fathoms. Many empty tubes, 

 perhaps of this species, dredged in Cape Cod Bay. Two specimens 

 from Gulf of St. Lawrence (Bay of Chaleurs, 11-15 fathoms). 



Distribution. — West Greenland, Faroes, Iceland, Swedish and 

 Danish waters, western Baltic, Gulf of St. Lawrence to Massachusetts, 

 central California, north Japan Sea. In 1 to 370 fathoms. 



Trochochaeta watsoni (Fauvel, 1916) 



Figure 83,h-k 

 Disoma watsoni Fauvel, 1916, p. 1, fig. l,a-i; 1932b, p. 28, pi. 1, figs. 8-11. 



Description. — The species was described originally from a single 

 anterior fragment of 9 segments. Two anterior fragments, the largest 

 of 32 segments, are referred to this species (collected by the Albatross). 

 The original description is supplemented to some extent but the 

 species is still incompletely known. 



Length?, width up to 2 mm., segments more than 32. Thoracic 

 region wider, somewhat flattened dorsoventrally, anterior abdominal 

 region narrower, cylindrical. Prostomium fusiform, rounded an- 

 teriorly or may be slightly notched, with a longitudinal crest extending 

 posteriorly on first setiger, with or without occipital antenna (absent 

 according to Fauvel; present on one spechnen, indistinct on the other; 

 perhaps it may be broken off). Tentacular palps not observed but 

 oval scars between base of prostomium and notopodia of fu'st segment 

 indicate their places of attachment. Notopodial and neuropodial 



569-457—63 21 



