10 



may be broadened and together with the claw may form a subchela 

 (Microphasma); sometimes the subchela is formed by the broadened 5th 

 and linear 6th article (Anchylomera, Phrosina); seldomly, a retractile 

 claw is present (Chuneolidae). 



Pereopods V are generally the longest and often (Phronimidae, 

 Phrosinidae, Microphasma) the strongest of all [the pereopods]. They 

 may be simple, with a retractile claw {Paralanceola, Lanceolidae, 

 Chuneolidae, Ctenoscina). In some groups a subchela develops, formed 

 by the dilatation of the 6th segment and the claw {Microphasma, 

 Microphasmoides) or by the distally broadened and strong 5th article and 

 the thinner, slightly bent 6th article (Phronimidae, Phrosinidae). The 2nd 

 article is often amygdaloid or teardrop-shaped (almost all Platysceloidea, 

 some Hyperiidae, Vibiliidae) or highly elongated; sometimes it is 

 triangular in transverse section and bears spines or denticles on its edges 

 or on the anterior and posterior margins (Scinidae, Cystisomatidae). 



Pereopods VI and VU, with a few exceptions, are shorter and weaker 

 than pereopods V; sometimes they have retractile claws (Lanceolidae, 

 Chuneolidae, Ctenoscina, Proscina), rarely, a subchela (Phrosina). The 

 2nd article in these is often enlarged and broadened, more sharply in the 

 Platysceloidea where this article forms the so-called "lateral shield". It is 

 particularly well developed in the Platyscelidae and Parascelidae where 

 the 2nd article of pereopods VI is unusually enlarged and broadened, 

 forming an operculum. Here the distal part of the leg is reduced and some 

 articles (usually the 4th and 5th) may fuse. By bending the abdomen, 

 these crustaceans close the entire lower part of the body with the enlarged 

 2nd articles of pereopods V-VII and turn into a firm, quick-sinking ball. 

 The tendency to form a strong lateral shield is found in some families of 

 the suborder Gammaridea (for example, Stegocephalidae, Stenothoidae) 

 but it always forms in them due to the growth of coxal plates. 



In females the gills and brood lamellae are attached to the base of the 

 coxal plates. The brood lamellae overlap each other on the ventral side and 

 form a brood chamber in which the eggs mature and hatching and develop- 

 ment of the young take place. There are usually five pairs of gills, located 

 on pereon somites II-VI, but in some groups their number decreases to 

 four, three, or even two pairs. The oostegites are located on somites II-V; 

 in the Rhabdosoma they are reduced and very few in number. 



The three pairs of natatory abdominal limbs (pleopods) are biramous; 

 their peduncle is one-segmented; both the rami (exopodite and endopodite) 

 are multisegmented and armed with long setae. By performing a natatory 

 function, these limbs create a current of water that bathes the gills or 

 young ones in the brood chamber. The lateral parts of the first three 

 abdominal somites enlarge, forming round epimeral plates (epimerons) 

 which laterally cover the tender natatory limbs. The lower posterior angle 



