MARINE GAMMARIDEAIsr AMPHIPODA 157 



Argissidae 



Figure 65 



Diagnosis. — Accessory flagellum 2-articulate; coxae 1 and 4 long, 

 coxae 1-3 successively smaller, coxa 4 larger than coxa 1; gnathopods 

 feeble, simple or poorly subchelate. Monogeneric. See Gammaridae, 

 Haustoriidae, Synopiidae, Ampeliscidae, Vitjazianidae. 



Description. — Accessory flagellum 2-articulate; when present, 

 primary flagellum basally conjoint in male; dorsal teeth only on 

 urosome, rostrum obsolescent; coxa 1 large, coxae 2 and 3 successively 

 smaller, coxa 4 larger than 1 ; mouthparts basic, upper lip slightly 

 incised; mandibular palp with article 3 longer than article 2; gnatho- 

 pods feeble, simple, except one species having gnathopod 1 poorly 

 subchelate; uropod 3 biramous; telson of medium length, cleft. 



Relationship. — ^Argissids are distinguished by the consecutive 

 reduction in size of coxae 1-3. They closely resemble Gammaridae, 

 especially the genus Megaluropus in which coxae 1-4 also are irregular 

 but in which coxa 2 is larger than 1 and coxa 3 smaller than 2. 



Despite their definitive similarity to Gammaridae, argissids bear 

 external resemblance to Haustoriidae and were at one time included 

 in that famUy. They call attention to the close relationship of haus- 

 toriids to gammarids. Again the unusual coxae distinguish them from 

 haustoriids. The peculiar eyes of Argissa hamatipes, four bigeminous 

 lenticular bodies imbedded at the periphery of a common pigmentary 

 mass, seem unique to the family but the other species of Argissa, A. 

 stebbingi, lacks eyes, so that they are not diagnostic. 



Sars (1895) has noted the similarity of the. genus Argissa to the 

 Ampeliscidae (at that time Argissa was placed in the Haustoriidae). 

 Resemblance occurs in the antennae, pereopods 1-2 and 5, the uropods, 

 and the telson. Argissa nevertheless has some primitive characters 

 which place it between the Ampeliscidae and the Gammaridae: the 

 accessory flagellum, the intermediately modified pereopods 3 and 4, 

 and a weakly 2-articulate outer ramus of uropod 3. The eyes of Argissa 

 may represent a stage in the development of the ampeliscid corneal 

 lens. Of course, Argissa cannot stand on the direct line between 

 Ampeliscidae and Gammaridae because of its specializations in coxae 

 but it may well be a close relative of the organisms that occurred 

 directly on the evolutionary pathway. The most important specializa- 

 tions of the Ampeliscidae have been the development of tube-spinning 

 glands in pereopods 1-2, a function apparently not developed in 

 Argissa, and the amalgamation of the last two pleonal segments. 



Article 2 of pereopods 3-5 in Argissa does have conspicuous glands. 



Vitjazianids have many characters in common with argissids but 

 Argissa may be recognized by the special configuration of coxae. 



