EXDEMISM IX THE NORTH PACIFIC 47 



Myriochele Malmgren, 1867 



Myriochele gracilis, new species 

 Plate 2, figs. 1-5 



Myriochele n.sp., Hartman, 1955, p. 177 



Collections: Many individuals come from San Pedro Basin, Cali- 

 fornia, in 26 to 440 fms (Hartman, 1955, p. 177). 



Tubes are uniformly small, measuring 15 to 20 mm long and 0.65 

 mm across at the greatest width. They taper distally to both ends, and 

 are externally neatly covered with a single layer of bits of siliceous sponge 

 spicules of uniform size (fig. 2). The animal within is about two-thirds 

 as long as the tube ; it adheres closely to the inner mucoid lining, and can 

 be removed only by tearing the tube to bits. It encompasses 18 setigerous 

 segments; externally it is smooth and unadorned except for the setae, 

 which project in stif^ series (fig. 1). 



The prostomium is subspherical (fig 1) and has an anteroventral oral 

 region; it extends back as a narrow neck region about as long as the 

 first setigerous segment. The first three segments are not unusually long 

 or short, but resemble those farther back. Uncini are first present from the 

 fourth setigerous segment arranged in short, transverse ridges, closely 

 appressed to the body wall, and present in the parapodia to the anal end. 

 As is typical of the genus, the uncini are very small and numerous and 

 all are essentially similar, except for the development of the distalmost 

 tooth. Each is long-shafted and terminates distally in a beaked hook; 

 there is a conspicuous shoulder (fig. 3). A smaller tooth (figs. 3-4) may 

 be present in varying stages of development, or it may be absent. The 

 pygidium is terminal and the anal end lacks ornamentation (fig. 1). 



In some of the collections from San Pedro Basin, one finds an occa- 

 sional anterior end, freed from a tube, which agrees with those dissected 

 out from the tubes in all essential details except for the larger size and 

 a pair of verj' long, tentacular processes emergent from the oral end 

 (fig. 5). The prostomium is similarly subspherical, the neck region is 

 prolonged to about the same degree, the first three setigerous segments 

 have like proportions, and the uncini are the same. The paired tentacular 

 processes are continuous with the dorsolateral part of the prostomium ; 

 they are longitudinally grooved on the ventral side, and conspicuously 

 splashed with dark brown pigment on their upper side. A pair of basal 

 enlargements is weakly separable from the base of the tentacles. From 

 their position and insertion on the dorsolateral side of the prostomium, 

 they appear to be branchial rather than palpal. 



