38 U.S. NATIONAL MUSETJM BULLETIN" 271 



The final manifold group in graph 1 is the greater isaeid complex 

 that might be accorded superfamily rank. The primitive isaeid is 

 conceived of as a morphological analogue to the basic member of 

 Gammaridae. Until one examines the fleshy telson and pereopodal 

 glands of primitive isaeids, one is struck by the great similarity of 

 generalized Gammaridae and Isaeidae (=Photidae). Isaeids have 

 become very diverse in many of the same ways as have the gammaridan 

 stock but no highly advanced inquilines have appeared, unless one 

 can link up some of the eophliantids; they instead appear to be 

 lignivores. Even so, the piercing-sucking groups like acanthonotozo- 

 matids, the coelenterate loving groups like the stenothoids and 

 amphilochids, tJie spongicolous and protochordate inhabiting kinds 

 have not evolved within the isaeid complex, perhaps because they 

 have been primarily adapted to form domiciles of their own out of 

 the pereopodal spinning glands. Identification and relationships are 

 clouded by the frequent loss of those glands in the Podoceridae, some 

 Corophiidae, the Cheluridae, and even the nomenclatorial type, 

 Isaea. A more basic example of the isaeid line is Gammaropsis and its 

 name should ideally be the root of the stock. 



The most advanced members of the isaeid group have accumulated 

 two morphological changes, either reversal in gnathopodal domination 

 or development of a partially to fully rigid urosome with loss of 

 uropodal structures. The gnathopodal reversal may be related to a 

 stronger than normal cephalic orientation required of organisms living 

 in tubes open to the anterior end of the animal body. Rigidization of 

 the urosome may assist the organism in maintaining a position within 

 the tube. Some of these tube dwellers have even returned to making 

 burrows (?internally lined) in the substrate. 



Perhaps the Podoceridae have come closest to the inquilinous func- 

 tion; their ecology and morphology are poorly known but there has 

 developed the impression that all their members have lost the spinning 

 glands and that many of them are strongly associated with hydroid 

 colonies, as if they were predatorial browsers. 



The stability and similarity among the mouthparts of the members 

 of the isaeid complex leads one to the view that podocerids belong with 

 the group. They are frequently mentioned as the root stock of caprel- 

 lids; indeed, since the time (Dec. 1965) that the contents of this paper 

 were formed, a new family, Caprogammaridae (Kudrjaschov and 

 VassUenko, 1966) has been described with further strong evidence of 

 podocerid-caprellid relationships. 



Distinctions between Isaeidae and Aoridae are not clear except that 

 gnathopod 1 of aorids is either larger than gnathopod 2 or is that 

 member having sexual dimorphism. The Corophiidae seem to be a 

 polyphyletic group of aorids and isaeids with pygidization. They may 



