ENDEMISM IN THE NORTH PACIFIC 53 



(fig. 6). These details are here shown for the first time. Their remark- 

 able resemblance to the flabelligerids is indicated. 



As the individuals have been preserved in formalin, the internal 

 organs are easily identified. All signs of segmentation are lacking except 

 in the midventral ganglia, where nine nodes are visible. The body con- 

 sists of eleven segments (Heath, 1930). There is no color except in 

 parts of the alimentary tract, including the green intestinal coil, the 

 brown gonadial organ immediately behind it, and the white mucus- 

 secreting anal gland at the far posterior end (Pickford, 1947). The single 

 pair of nephridia are visible at the forward end dorsal to the alimentary 

 tract and the shorter buccal pouch lies ventral to the gut. The cardiac 

 body lies over and in front of the intestinal coil. 



The prostomium and peristomium are completely fused ; together 

 they surround the oral aperture. A slight convexity at the middorsal end 

 of the upper lip may represent the prostomium. There are no visible eyes 

 or other pigmented light receptors. The large, paired palpi are inserted 

 dorsolaterally and are longitudinally ridged along their entire length 

 (fig. 6). A pair of conspicuous nuchal grooves is located at the posterior 

 base of the palpi and a similar grooved structure lies farther back extend- 

 ing across the middorsum. These ciliated depressions resemble the nuchal 

 organs of other sedentary polychaetes (Rullier, 1950, pp. 18-24). 



The body behind the nuchal organs is slightly constricted, though not 

 set off from the following tentacular region. The tentacles form a trans- 

 verse paired series, numbering five to seven long tentacles on a side ; they 

 are separated middorsally by a narrow smooth space. These tentacles 

 differ from the palpi in that they are shorter, smaller, and cylindrical 

 instead of grooved. 



The prostomium, peristomium, palpi and tentacular region are 

 capable of being withdrawn into the buccal cavity so that in retraction 

 the tentacles are directed forward (Heath, 1930, pi. 1, fig. 4) ; the 

 palpi are then neatly folded in the buccal pouch. 



These cephalic structures, preceding a trunk region that is thickly 

 sheathed in a gelatinous membrane, recall the similar parts present in 

 species of Flabelligera Sars, family FLABELLIGERIDAE. The re- 

 semblances extend to some anatomical parts. Reduction of nephridial 

 pairs to a single one at the anterior end is known in F. diplochaitos and 

 some other sedentary polychaetes. Transverse septa are reduced in num- 

 ber; the musculature of the body wall is reduced except in the cephalic 

 region ; the alimentary tract is bent on itself ; a cardiac body is extensive 

 (Giinther, 1912, pp. 93-186). The anterior end, including palpi, ten- 

 tacles and accessory parts, is completely retractile into the buccal region. 



