499 



well developed, occupying the entire head, and are sometimes so hyper- 

 trophied that constitute the most massive part of the crustacean body. 

 The rostrum is well developed, pointed and projects in front of the eyes, 

 sometimes greatly elongated, and constituting in length a considerable 

 part of the body. Antennae I are articulated with the ventral side of the 

 base of the rostrum; in males their basal segments are thickened, curved, 

 and densely pubescent; the flagella are three- to four-segmented. Anten- 

 nae II are reduced in females, in males greatly elongated, folded zigzag 

 and articulated with the ventral part of the head. The mandibles have a 

 three-segmented palp, developed only in males. The maxillae are absent. 

 The maxillipeds are very small, with short outer lobes and a median lobe 

 barely reaching the middle of the outer. 



Pereopods I and II have chelae or subchelae. The 2nd segment of 

 pereopods V-VII is ovavtely broadened, but not modified into a covering 

 plate, as in the family Platyscelidae. Pereopods III-IV have narrow vir- 

 gate segments. The distal part of pereopods VII is normally developed, 

 rarely reduced to one-three segments. The coxal plates in representatives 

 of various genera may be fused with the pereon or may be free. The 

 pleopods are relatively weak and cannot ensure a high speed of swim- 

 ming. Uropods I have free rami; the endopodites of uropods II-III are 

 sometimes fused with the basipodites. The telson is fused with the last 

 urosomite; sometimes a faint border is discernible between them. 



An interesting morphological peculiarity of Oxycephalidae is the 

 heteromorphic development of the gills, which has been related to their 

 active role in the formation of brood chambers (Fage, 1960). In males the 

 gills are elongated and folded, which increases their contact surface; in 

 females only the last pair of gills are similar structure while the anterior 

 gills are modified into thin, smooth, broadly oval plates. The gills are 

 404 usually developed on pereon somites II-VI, but sometimes absent or 

 rudimentary on somites II-IV. The oostegites (on somites II-V or III-V) 

 are too narrow to form a snug closed chamber. This is achieved by the 

 simultaneous action of the gills and oostegites but the role of these two 

 organs in the formation of the brood pouch [chamber] varies in different 

 representatives of the family. 



The family comprises eight genera, of which five are monotypic and 

 the rest include a few species. 



KEY TO GENERA OF FAMILY OXYCEPHALIDAE 



1. Body very long and thin; piliform rostrum and urosome together 2/3 



total body length 8. Rhabdosoma white. 



— Body weakly elongated; rostrum triangular, not piliform, and together 

 with urosome 1/4 total body length 2. 



