154 PART II. SYSTEMATIC ACCOUNT 



1. Order ATHECANEPHRIA IVANOV, 1955 



The first coelom is sac-shaped, and its coelomoducts are wide apart, with 

 their excretory sections closely adjoining the lateral cephalic vessels. There 

 is a pericardium close to the dorsal part of the heart, and the protosoma is 

 separate from the mesosoma. There may be only one tentacle (in the genus 

 Siboglinum), or if there is more than one they are always separate. On the 

 dorsal side the postannular region of the metasoma bears metamerically 

 arranged glandular sections of the epidermis or solitary glandular shields, and 

 on the ventral side there may be a solitary large papilla opposite each of these. 

 The spermatophores are spindle-shaped. The greater part of the tube is 

 ringed and sometimes also segmented, while the anterior section is flimsy, 

 with delicate, growing walls which collapse easily. 



The Athecanephria includes two families, the more primitive Oligo- 

 brachiidae, and the unitentaculate Siboglinidae, characterized by secondary 

 simplification. 



I. Family Oligobrachiidae Ivanov, 1957 



[The recent discovery of Nereilinum and Siboglino'ides has necessitated 

 revision of the diagnosis of the Oligobrachiidae. The revised diagnosis is 

 given here instead of the one given in the Russian edition of this book. 



The Oligobrachiidae are Athecanephria with a small number of tentacles, 

 usually six to twelve, but sometimes reduced to a single pair. The base of the 

 tentacular crown is horseshoe-shaped, and the pinnules lie along the 

 tentacles in two rows. Papillae are not usually developed in the preannular 

 part of the trunk, nor is there any sign of secondary metamerism in this 

 region (except in Birsteinia). There are three genera - Oligobrachia, Bir- 

 steinia and Nereilinum. Type of the family: Oligobrachia Ivanov.] 



/. Genus Oligobrachia Ivanov, 1957 



Ivanov, 1955a: 177 (nom. nud.); Ivanov, 1955b: 382 (nom. nud.); Ivanov, 1955d: 

 173, 174 (nom. nud.); Ivanov, 1956b: 1864 (nom. nud.); Ivanov, 1956c: 165, 169 (nom. 

 nud.); Abrikosov, 1957: 236; Alvarado, 1957b: 495; Ivanov, 1957a: 433-9, 490, 491, 493, 

 495-8; Ivanov, 1957b: 1127, 1128, 1134-8; Beklemishev, 1958: 367; Dajoz, 1958: 231, 

 232, 234, 235; Ivanov, 1958a: 1369; Ivanov, 1958b: 1682; Ivanov, 1958d: 1; Ivanov, 

 1958e: 1070, 1075-8; Manton, 1958: 750; Ivanov, 1960a: 1528, 1530, 1531, 1535, 1538, 

 1539, 1541, 1550, 1560, 1573, 1590, 1593, 1601, 1603, 1606, 1614, 1620; Ivanov, 1960c: 

 5, 11, 12, 15, 19, 24, 27, 37, 48, 60, 76, 87, 89, 91, 98, 105, 106, 107, 114, 115, 116, 220. 



