299 



central part which are important in the identification of the species. Ante- 

 rior to the oral appendages, two rows of denticles occur, which proceed 

 forward from the outer margins of the mandibles; anterior tooth is the 

 largest and following (glandular) more poorly developed teeth, present in 

 specimens of all species; moreover, second tooth is homologous with the 

 rudiment of antennae II, this is confirmed by a gland opening at its base 

 (Stebbing, 1888). The number of rest denticles forming the arcuate rows 

 may vary in different species from zero to six in each row; sometimes 

 asymmetry of number is observed on the right and left. 



The pereon is longer than the pleon, the somites are separated by 

 deep grooves (except the first two), and each somite bears several denti- 

 cles dorsally. The first (geminate) somite of the pereon is very narrow and 

 the border between the fused somites in the form of a shallow groove. 

 The coxal plates are fused with the pereon. The so-called coxal spine, 

 developed to a variable extent in different species, is located above the 

 base of the 2nd segment of pereopods I-II. The chelae of pereopods I-II 

 are well developed and the legs, not longer than the 2nd segment of 

 pereopods III, closely adjoin the oral appendages and form with them 

 a unified functional complex. Pereopods III-IV consist of long narrow 

 segments. Pereopods V are the longest. In adult females the distal part of 

 the 6th segment, especially in pereopods VII, is often broadened because 

 of the strong development of the glandular tissue. The 2nd segment of 

 pereopods VII is proximally more or less broadened, especially in males. 

 In adult females the distal part of pereopods VII is modified into the so- 

 called egg forceps (Woltereck, 1903): the distal end of the elongated 6th 

 segment bulges, has a concave surface (notch conforms to size of the 

 egg), and the claw is steeply curved, movable, and perhaps prevents the 

 egg from falling during its transfer from the opening of the oviduct into 

 the brood chamber. 



The urosome (without uropods) is shorter than the pleon. Even traces 

 of uropods II are absent. The rami of the uropods are shorter than the 

 basipodites. 



Type species: Cystisoma neptunus Guerin-Meneville, 1842. 



Notes: Records of Cystisoma are few to date. This is because of the 

 deepwater habitat of this genus and its notably sparse populations. Due 

 to wide age-related changes and sexual dimorphism as well as incom- 

 plete initial descriptions, an unjustifiably high number of species have 

 been included in this genus. According to Barnard (1932):"It would be 

 more correct to say about this genus that we are describing the specimens 

 and not the species." Only Pirlot (1938) was able to understand its sex- 

 ual dimorphism, a very confusing character; the majority of the earlier 

 researchers mistook young females for males with rudimentary oostegites 

 (!). As a result, in describing the male subsequent researchers sometimes 



