DIPLOBRACHIA SOUTHWARDAE 



383 



The bridle lies a little in front of the middle of the fore-part of the body. 

 Its thin keels fuse neither dorsally nor ventrally (Fig. D\S2A y B). Under 

 sufficiently powerful magnification their structure can be observed: on the 

 ventral side of the body a row of cuticular rodlets is attached to the posterior 

 side of the narrow homogeneous colourless main axis of the keels (Fig. 

 D152D) — an unexpected character to find in a species of the genus Diplo- 

 brachia, but one encountered in a few other forms (e.g. in Heptabrachia 

 ctenophora and Lamellisabella ivanovi). There is a rather sharp mid-ventral 

 furrow in front of the bridle (Figs. D152i?, E152v4), and behind it a slight 

 waist (Fig. D 152.4). The coelom of the 

 mesosoma contains numerous flask- 

 shaped glands, but none lies in front 

 of the bridle. The mesosoma is divided 

 from the metasoma by a simple 

 annular groove. 



The metameric section of the trunk 

 is very short but has a well-developed 

 dorsal ciliated band (Fig. D152y4) 

 and ventral sulcus. In its front half 

 the latter is narrow and bounded at 

 the sides by broad smooth ridges; 

 farther back the sulcus opens out and 

 the ridges disappear (Fig. D152£). 

 Adhesive papillae are developed only 

 in the hind half of the region. It is 

 possible to observe the pyriform 

 glands, lying within the lateral ridges, 

 assembled at the front end into longi- 

 tudinal tracts which break up farther 

 back into rounded metameric groups 

 of glands. There are usually three or 

 four pairs of such groups, each con- 

 taining four to six glands. A little 

 farther back again these gland-groups 

 become located within well-differen- 

 tiated oval or round papillae, projecting 

 above the surface of the ridges (Fig. 

 D152£). The number of papillae, to 

 judge from six individuals, varies from 



0.1 мм 



Fig. El 52. Diplobrachia southwardae: 

 A - the protosoma from the ventral side; 

 В - the cephalic lobe from the dorsal 

 side. 



с - cephalic lobe;/- bridle; tns - meso- 

 soma; ps - protosoma; s 1 - groove be- 

 tween the protosoma and mesosoma; 

 i* - post-tentacular groove ; / - tentacle. 



