J46 • DISCOVERY REPORTS 



Family SPIONIDAE 



Genus Pygospio, Claparede 

 Pygospio dubia, n.sp. 



St. 29. 16. iii. 26. West Cumberland Bay, South Georgia. 5-9 miles S 51° W of Jason Light. 

 23 m. Gear DC. Bottom : mud and stones. About fifty specimens. 



Description. The average size is about 10 mm. by i mm. at the widest part. The 

 body is tapered at both ends, the widest part being at about the 7th chaetiger. All 

 colour has disappeared in spirit. The prostomium (Fig. 55, a) is subtriangular. In 

 front it is very slightly indented in the middle, and the corners are prolonged into small 

 rounded eminences: there are no frontal horns. It is continued back to the edge of the 

 2nd chaetiger and ends in a minute occipital tentacle. There is a pair of very long 

 grooved palps, in some examples more than half the length of the body. I can see no 

 trace of eyes. 



In the anterior segments the lamellae are semi-oval and equally developed. The ist 

 chaetiger has fully developed dorsal and ventral rami but no gill. On the 2nd and 3rd 

 chaetigers (Fig. 55, b) there is a finger-shaped gill quite separate from the dorsal lamella. 

 The 4th and 5th chaetigers (Fig' 55, c) have no gill, but from the 7th to the 13th 

 chaetiger (Fig. 55, d) there are gills more than twice the size of those of the 2nd and 

 3rd chaetigers and fused with the dorsal lamellae, except at the tip which is free. 



In the posterior segments (Fig. 55, e) the lamellae are equally developed, the dorsal 

 being broadly lanceolate and the ventral more papilliform. They are both small. There 

 are capillary bristles (Fig. 55,/) bordered very slightly, if at all, in the dorsal and ventral 

 rami. Between the 17th and 20th chaetigers, hooks (Fig. 55,^) appear in the ventral 

 rami. These seem to be perfectly plain hooks lacking both a second tooth and a hood. 



The pygidium is very puzzling. In some examples, apparently complete posteriorly, 

 the body tapers simply to a point with an anus without anal cirri (Fig. 55, h); and in 

 others there is a distinct pygidial sucker consisting of two vertical valves, which under 

 the microscope have the appearance of oyster shells (Fig. 55, /). There are no neuro- 

 podial glandular pockets and I can discover no sexual pouches. The state of preservation 

 was inadequate for an examination of the dorsal organs. 



Remarks. This is a young form. The presence of an occipital tentacle, or at any rate 

 a minute process at the base of the tapered prostomium, of an anal sucker, of hooks 

 in the ventral rami only, of gills beginning on the 2nd chaetiger and continuing fused 

 with the dorsal lamellae from the 6th to the 13th chaetiger only, and the absence of 

 frontal cornua and a modified 5th chaetiger place this form nearer to Pygospio than to 

 any other genus. Moreover, the interrupted arrangement of the gills recalls that in the 

 male of P. elegans. 



My specimens are immature, and as far as I can discover they show no sexual 

 dimorphism. They may, however, be the young of a Polydora in which the 5th chaetiger 

 is not yet modified. 



