OLIGOBRACHIIDAE 155 



There are 6-9 tentacles on which the pinnules lie in double alternating 

 rows. The cephalic lobe is not demarcated, but the protosoma is separated 

 from the mesosoma by a slanting groove. There are no plaques. The pre- 

 annular region of the trunk lacks any trace of metameric papillae, but, instead, 

 there are continuous lateral glandular ridges. A trace of metamerism is 

 visible on the postannular region, however, where irregular glandular areas of 

 the dorsal integument are arranged more or less in this way. The spermato- 

 phores are spindle-shaped and the tube is unsegmented, with regular rings. 



The absence of metamerism in the anterior part of the trunk, the mere 

 trace of it in the postannular part and the small number of free tentacles, 

 arranged in a horseshoe at their base, show that Oligobrachia is the most 

 primitive genus among the Pogonophora (p. 141). 



Type of genus : Oligobrachia dogieli Ivanov. 



Key for the identification of the species of the genus 



Oligobrachia 



1 (2) The papillae of the zone of thickening bear semilunar plaques, 



about 30-35/x across, thickened along the front edge. The cephalic 

 lobe and the part of the mesosoma behind the bridle are glandular. 

 There is a pair of longitudinal stripes alongside the dorsal ciliated 

 band. The tube is black and the rings stick out above its surface. 



0. ivanovi (p. 160). 



2 (1) There are no plaques on the papillae of the zone of thickening. The 



cephalic lobe and the mesosoma are not glandular. There are no 

 longitudinal dorsal stripes. The brown rings of the tube are not 

 protuberant. 0. dogieli (p. 155). 



1. Oligobrachia dogieli Ivanov (Figs. 89-92) 



Ivanov, 1957a: 434-9, 490-3, 495-7, Figs. 1-5, 59; Alvarado, 1957b: 495; Ivanov, 

 1957b: 1127, 1128, 1134-8, Figs. 2, 12-14; Dajoz, 1958: 231, 235; Ivanov, 1958a: 1369; 

 Ivanov, 1958b: 1682, Figs. 1,4: Ivanov, 1958d: 1; Ivanov, 1958e: 1070, 1075-8, Figs. 

 6-8; Manton, 1958: 750, Figs. 17, 20, 22; Ivanov, 1960a: 1531, 1536, 1542, 1550, 1562, 

 1567, 1592, 1593, 1600, 1604, 1606, 1608, 1611, 1612, Figs. 1397, 1399, 1424, 1428, 1432, 

 1452, 1460, 1462, 1463 PI. VII; Ivanov, 1960c: 5, 9, 10, 15, 19, 22, 36, 50, 54, 78, 85, 89, 

 91, 92, 93, 95, 96, 105, 116, 145, 265, Figs. 15, 17, 43, 48, 52, 71, 79-81, 87, 89-92, PI. II. 



The length of the anterior section (the protosoma together with the 

 mesosoma) is 8 times greater than the breadth. The small protosoma is 

 limited behind by a deep groove whose ventral ends do not meet, while the 

 dorsal part makes a backwardly directed right-angle, overlapping the dorsal 



