52 HARTMAN 



The tube is chalky white, approximately cylindrical at its distal or 

 free end, or flattened where attached to a substratum. Its external sur- 

 face is somewhat rugose due to the presence of irregularly spaced annu- 

 lated ridges (plate 4). Its maximum length is 36 mm or more. A single 

 living pecten shell may have five serpulid tubes in varying stages of de- 

 velopment, with the largest tube extending posteriorly beyond the mol- 

 lusk. All of the tubes are attached to the dorsal or left valve of the 

 mollusk, and usually directed so that the oral aperture of the annelid is 

 at or near the siphonal end of the mollusk. A kind of commensalism is 

 suggested by the relative positions of the tubes on the shell. 



The pecten has been determined to be an undescribed species of 

 Cyclopecten Verrill, 1897 (fide Mr. Gilbert Grau). Both it and the 

 serpulid have been found almost invariably in the deepest parts of San 

 Pedro Basin, California, where they are associated with tubes of a 

 deep-water chaetopterid. 



Distribution : Protis pacifica is known only from deep water of¥ the 

 coast of southern California. 



POEOBIIDAE Heath, 1930 



Poeobius meseres Heath, 1930 

 Plate 1, fig. 6 



Poeobius meseres Heath, 1930, pp. 223-249, 2 figs., 3 pis. ; Pickford, 1947, 

 pp. 287-319, 3 pis. 



Collections: Numerous specimens were taken from deep water tows 

 off northern California, Sept. 1, 1951, at station 30 of the Northern 

 Holiday Cruise, by Dr. Martin W. Johnson, to whom I am indebted 

 for a gift of the specimens. 



Poeobius meseres is associated with chaetognaths, which resemble 

 it in shape, size and general appearance. The two differ grossly in that 

 Poeobius has no setigerous oral end. The overall length is about 25 mm. 

 The conspicuous lateral compression of the body increases from the 

 anterior third of the body to the tail, so that there appear to be dorsal 

 and ventral keels. In some individuals the anterior end is completely with- 

 drawn (as shown by Heath, 1930, pi. 1, figs. 1, 4) into the gelatinous 

 sheath which encompasses the body. In others the prostomium and an- 

 terior structures are extruded so that their natural relations are visible 



