264 U.S. NATIONAL MUSEUM BULLETIN 271 



Parargissa Chevreux 



Parargissa Chevreux, 1908c. — Birstein and Vinogradov, 1958. 

 Protohyperiopsis Birstein and Vinogradov, 1955. 



Type-species: P. nasuta Chevreux, 1908c (original designation). 

 Species: 5, cosmopelagic, abyssal. 



Isaeidae 



[including Photidae] 

 Figures 103-106 



Diagnosis. — ^Accessory flagellum variable in length or absent; telson 

 entire, short, fleshy; coxa 5 not excavate posteriorly; pereopods 1-2 

 glandular; uropod 3 rarely projecting beyond uropods 1 and 2, rami (at 

 least one) as long as or longer than peduncle, occasionally uropod 3 

 uniramous. See Aoridae, Corophiidae, Ischyroceridae, Calliopiidae, 

 Laphystiopsidae, Oedicerotidae, Pleustidae. 



Description. — Accessory flagellum varying from absent to long 

 and multiarticulate; body smooth, rostrum absent; coxae rounded or 

 quadrate ventrally, long or short, fourth not excavate posteriorly; 

 mouthparts basic; gnathopods usually powerfully subchelate or 

 extremely setose; uropod 3 short, rami as long as or longer than pe- 

 duncle, not uncinate, occasionally inner ramus reduced or absent; 

 telson entire, short, fleshy, nearly circular or square, occasionally 

 falsely cleft. 



Relationship. — The Isaeidae do not warrant distinction from the 

 Photidae on the basis of prehensile or partially subchelate pereopods 

 and so they must be joined, Isaeidae (Isaeinae Dana, 1853) taking 

 precedence. This move is unfortunate because of the long use of the 

 name Photidae for a diversity of genera and the relatively infrequent 

 use of the name Isaeidae. 



The Laphystiopsidae have a nontriturative mandibular molar and 

 are otherwise like calliopiids and pleustids. 



See Calliopiidae for calliopiid-pleustid differences. 



The Gammaridae usually have a cleft telson; when entire, the telson 

 is not circular or subcircular and coxa 4 is strongly excavate posteriorly; 

 some Gammaridae have a small, square, unexcavate coxa 4 but in 

 those species the telson is cleft; Gammaridae lack glandular pereopods, 

 do not build tubes, usually have uropod 3 projecting beyond uropods 

 1 and 2 and the rami are enlarged, either by dorso ventral depression, 

 elongation, or foliaceousness. 



The Aoridae have gnathopod 1 larger than gnathopod 2. Linkage is 

 shown to that family by Aorcho, in the Aoridae, having gnathopods 1 



