36 U.S. NIATIONAL MUSEUM BULLETIN 271 



Direct advancement to the Lafystiidae through reduction in maxil- 

 lipedal palps is a consequence of acanthonotozomatid specialization 

 and the ultimate is reached in the Ochlesidae, technically hyperiids, 

 because of the complete loss of palps. 



Stegocephalidae are the only other major group of Gammaridea 

 with the strong piercing and sucking mouthpart field of acanthono- 

 tozomatids and even though their coxae are not as acuminate and 

 then- mandibular palps and molars have been lost, there is still merit 

 in considering a direct relationship between the two families. Stego- 

 cephalidae have the broad, sublaminar mandibles of several acantho- 

 notozomatids but may have originally evolved as a pelagic group, 

 some members having returned to the benthos in later stages. The 

 breadth of the lateral shield appears to have a relationship to midwater 

 suspension but acumination may still be seen in the anterior coxae. 

 The benthic members may also be predatorial grazers and the only 

 known raptorial predator in the benthic Gammaridea is a member of 

 the Stegocephalidae. 



Another line of evolution favoring inquilinous behavior is that 

 commencing with the Amphilochidae and Leucothoidae. Early stu- 

 dents of the Gammaridea noticed similarities between Liljeborgiidae 

 and Leucothoidae in maxillipedal structures ; other resemblances such 

 as retention of enlarged gnathopods are so clear that one might say 

 that leucothoids are liljeborgiids in which the accessory flagellum has 

 become vestigial and gnathopod 1 has been transformed into its fully 

 carpochelate condition while the outer plates of the maxillipeds 

 became vestigial. The rudiments of the carpochelate gnathopod may 

 be seen in gnathopod 2 of leucothoids, thus resembling the gnathopods 

 of liljeborgiids. Anamixids carry the inquilinous state to the ultimate 

 by the transformation of mandibles and maxillae into a piercing keel. 



Amphilochidae may stand almost completely alone. Their mouth- 

 parts strongly resemble those of liljeborgiids and their gnathopods are 

 usually miniaturized editions, like those of Listriella. But their heads 

 have the appearance of the pleustid-paramphithoid or bateid line. 

 The primary mark of their advancement is the reduction of coxa 1, 

 not as fully reduced as in the Bateidae. This suggests their direct 

 precursorial relationships to the stenothoids. The peculiar Pseudam- 

 philochus, through its cleft but ovato-acuminate telson, unreduced 

 coxa 1, large rostrum and nonelongate peduncle of uropod 3, stands 

 among the Amphilochidae, Pleustidae, and Liljeborgiidae. Schellen- 

 berg (1931) suggested that it should be assigned to a unique family, 

 the Pseudamphilochidae. 



All five families of the stenothoid complex seem to have strong 

 interrelationships by virtue of the mandibular form (see figures) in 

 which at least one mandible has a box-like shape with deeply serrate 



