MARINE GAMMARIDEAN AMPHIPODA 421 



small, occasionally weakly spinose, nontritiirative protuberance; 

 palp of maxilla 1 biarticulate (often obscurely) ; maxillipedal palj) 

 article 3 not produced, article 4 short, with one or a few apical 

 spines or setae; article 2 of pereopod 3 slender, scarcely wider than 

 article 3; eyes absent; rami of uropod 2 hearing distal spines or setae 

 (Harpinia and Harpiniopsis) . Species: about 8, antarctic littoral 

 and probably cosmopolitan in bathyal-abyssal. 



Pleustidae 



Figures 152, 153 



Diagnosis. — Accessory flagellum composed of a small scale or ab- 

 sent; lower lip formed of two oval outer lobes obliquely astride nearly 

 coalesced inner lobes; telson entire; upper lip incised. See Calliopiidae, 

 Paramphithoidae, Liljeborgiidae, Isaeidae, Eusiridae, Ampithoidae, 

 Amphilochidae, Ischyroceridae, Laphystiopsidae, Oedicerotidae. 



Description. — Body with or without dorsal processes; rostrum 

 long or inconspicuous; accessory flagellum vestigial; upper lip incised; 

 mandibles bearing a 3-articulate palp, molar triturative or nontritura- 

 tive; lower lips characteristic (see diagnosis); remaining mouthparts 

 basic, article 3 of palp of maxilliped occasionally produced; gnathopods 

 subchelate, feeble or powerful; coxae of medium length or long; 

 uropod 3 with rami much longer than peduncle, lanceolate, outer 

 ramus usually shorter than inner; telson entire or apically sculptured, 

 cleft nearly one fifth in one species of Austropleustes. 



Relationship. — One genus of Amphilochidae, Amphilochoides, pos- 

 sesses a lower lip like those of pleustids but most amphilochids can 

 be characterized by the small, partially hidden coxa 1, and some 

 amphilochids have both coxae 1 and 2 concealed. Pseudamphilochus 

 however has a normal coxa 1 and cleft telson and thus resembles one 

 species of Austropleustes. See family key G for distinctions. 



Only the shape of the lower lip separates this family from the 

 Calliopiidae. Two genera, Harpinioides and Mesopleustes, have lower 

 lips intermediate between the two families. 



The Laphystiopsidae are very similar to the Pleustidae and further 

 study is needed to clarify their systematic position. 



Key to the Genera of Pleustidae 



1. Mandibular molar with a triturating surface composed of ridges and teeth 



(fig. 1536) 2 



Mandibular molar a simple, small, smooth hump (fig. 153c) 5 



2. Maxillipedal palp article 3 bearing a distal process (fig. 153i). 



Stenopleustes 

 Maxillipedal palp article 3 lacking a distal process (fig. 153A) 3 



