POLYBRACHIIDAE 333 



I. Family Polybrachiidae Ivanov, 1952 



The Polybrachiidae are Thecanephria with free tentacles. The base of the 

 tentacular crown is a horseshoe, but the ends may be bent round to com- 

 plete the ring. The pinnules on the tentacles form two or more rows. 



The family includes the following genera: Heptabrachia, Cyclobrachia, 

 Diplobrachia, Zenkevitchiana, Polybrachia and Galathealinum. The genus 

 Krampolinum (p. 393) may also be regarded as belonging to this family. 



/. Genus Heptabrachia Ivanov, 1952 

 Ivanov, 1952: 375, 387-90; Zenkevich, 1954: 76, 80; Zenkevich, Birstein and Belyaev, 

 1954: 68; Ivanov, 1954b: 72, 75, 76, 79; Hartman, 1954: 185; Ivanov, 1955a: 177; 

 Ivanov, 1955d: 173, 174; Ivanov, 1956b: 1864, 1868; Ivanov, 1956c: 165, 169; Jagersten, 

 1956: 238; Kirkegaard, 1956b: 186; Abrikosov, 1957: 233; Ivanov, 1957a: 439, 449, 

 461-9, 470, 475, 490-7; Vinogradova, 1958: 112; Dajoz, 1958: 231; Fell, 1958: 46; 

 Ivanov, 1960a: 1528, 1538, 1539; Ivanov, 1960c: 5, 11, 23, 24, 106, 114, 199, 215, 220. 



There are 5-13 free tentacles forming a horseshoe at the base (the 

 earlier report, Ivanov, 1952, 1957a, that Heptabrachia abyssicola had its 

 tentacles arranged in a ring, is incorrect (Ivanov, 1960c)). The cephalic lobe 

 is not divided from the protosoma, but the latter is divided from the meso- 

 soma by an annular groove, and in a few species secondary transverse grooves 

 are present on the mesosoma in front of the bridle, whose keels may be either 

 fused on the ventral side or some distance apart. The front part of the trunk 

 has round or oval cuticular plaques. The spermatophores are small and leaf- 

 shaped, tapering from one end to the other. The tube is ringed. 



Eight species are known: Heptabrachia abyssicola Ivanov, H. gracilis 

 Ivanov, H. subtilis Ivanov, H. beringensis Ivanov, H. talboti Southward 1961, 

 H. ctenophora Ivanov 1962, H. canadensis Ivanov 1962, and H. celebensis 

 (Southward 1961). 



Key for the identification of the species of the genus Heptabrachia 



1 (10) In front of the bridle the mesosoma is scored by one or two second- 



dary annular grooves. The adhesive cuticular plaques are oval. 



2 (7) The ventral ends of the keels of the bridle fuse or touch. There are 



four to eight tentacles. 



3 (6) There is a single secondary mesosomal groove. The plaques of the 



metameric papillae are about 20/x, across. 



4 (5) There are three to five papillae in each transverse row in the post- 



annular region. The front edges of the plaques on the metameric 

 papillae are smooth. The toothed platelets are 16/г long. The tube 

 has regular rings which are very unequal in length. 



2. H. gracilis (p. 338). 



м* 



