MARINE GAMMARIDEAN AMPHIPODA 231 



Marine Gammaridae 



Figures 94-96 



Diagnosis. — Like the basic gammaridean, from which all other 

 diagnoses in this paper are used to distinguish families, but accessory 

 flagellum occasionally reduced to one long article, maxillipedal palp 

 occasionally 3-articulate, gnathopod 1 rarely larger than 2, telson 

 occasionally uncleft, inner ramus of uropod 3 reduced, coxae 1-4 

 rarely of nonuniform shape, coxa 4 occasionally not posteriorly 

 excavate and pereopod 5 rarely elongate. 



Description. — ^The Gammaridae are variable and many genera 

 form links to other famiUes. Accessory flagellum always present but 

 varying from one long article to more than 20 short articles; peduncle of 

 antenna 1 elongate; rostrum present or absent; upper lip not incised; 

 mandible always bearing strong triturative molar and 3-articulate 

 palp; lower lips variable, never ampithoid or pleustid in structure; 

 maxillae fully developed, not strikingly foliaceous; palp of first maxilla 

 2-articulate ; maxillipeds with well-developed plates, palp 3- or 4- 

 articulate; gnathopods usually powerful and subchelate, occasionally 

 slender and simple, gnathopod 1 rarely larger than 2; coxae of medium 

 length, occasionally shortened; coxa 4 occasionally not excavate 

 posteriorly; uropod 3 highly variable but rami never shorter than 

 peduncle (except Parapherusa, Falkland ella, and Gammarella) and 

 usually flattened, not cylindrical, generally lanceolate, foliaceous or 

 subquadrate, inner ramus occasionally very short; telson not elongate 

 (except Parapherusa), usually deeply cleft but occasionally broader 

 than long, uncleft or emarginate. 



Relationships. — Gammaridae are difficult to define precisely be- 

 cause so many genera have exceptional morphology. Four of the 

 genera have uncleft telsons and thus resemble Calliopiidae but all have 

 well-developed accessory flagella. They may also resemble some of the 

 isaeid-Hke famihes but their telsons are not fleshy (not thickened 

 dorsoventrally). The most difficult member of this quartet is Para- 

 pherusa Stebbing which confounds all possible simplifications made 

 in the keys and diagnoses of famihes and genera. The unique species 

 of this genus has a third uropod resemblnig that of ischyrocerids or 

 ampithoids (fig. 96d), unexcavate coxa 4, and its telson is entire but 

 elongate, uropod 1 has a ventrodistal peduncular tooth like that of 

 various ischyrocerids and isaeids. The absence of pereopodal glands 

 apparently demonstrates its correct assignment to the Gammaridae, 

 rather than to the glandular famihes. The other marine gammarid 

 genera with uncleft telson have deep posterior excavations on coxa 4 

 and thus cannot be confused with isaeid-like genera. One ischyrocerid, 

 Bathyphotis, however, has a strongly excavate coxa 4 and has a special 



