GAMMARIDEAN AMPHIPODA 23 



have not been solved. The complex of "northern" species, those 

 with slender, poorly palmate first gnathopods, is especially difficult 

 to resolve and one must consider the possibility that A. lindbergi, 

 A. plea, A. "mea," and A. tea are all morphs of a single epigenotype. 

 In southern California Ampithoe pollex and A. simulans ( = A dalli) 

 are extremely difficult to differentiate because A. pollex appears to 

 have at least 2 phenotypes (as evidenced by color in alcohol, hence 

 artificial). Possible hydridization has been detected but not thoroughly 

 investigated in several specimens. 



The nomenclatural history of Eurystheus thompsoni has been the 

 most confused of that of any Californian amphipod, owing in part 

 to the radical morphological changes which occur at sexual maturity. 

 The most remarkable of those changes is the enormous increase 

 in size of the male seventh coxae, a change unique to this gamma- 

 ridean and its phylon from the Gulf of California (Barnard, 1968). 

 Other species of Eurystheus, Megamphopus and even Aoroides re- 

 semble E. thompsoni ( = E. tenuicornis, =Podoceropsis concava) 

 but the minute dorsal ornamentation of the fourth pleonite is dis- 

 tinctive for E. thompsoni. 



Stenothoids are poorly represented in the Californian intertidal; 

 they are small, 1 to 3 mm. in adult length and many of them may 

 have been lost in the screening of the samples. They are extraor- 

 dinarily difficult to identify generically because of taxonomic de- 

 pendence on palps of mouthparts. However, those so far discovered 

 have diverse combinations of gnathopod 1, shapes of pereopods 

 3-5, coxa 4, antennal lengths, eyes and minute ornamentation of 

 pereopodal dactyls. Excision of mouthparts for identification of 

 each specimen is therefore not necessary. 



Juveniles of ischyrocerids, photids, ampithoids, and small-bodied 

 species of Eurystheus and Megamphopus form a high "background" 

 count in Californian intertidal samples. The ischyrocerids may be 

 recognized by the elongation of the third uropodal peduncle, the 

 rami being short and styliform. In contrast, ampithoids have stout, 

 stubby, even shorter rami than those of ischyrocerids. Jassa falcata, 

 the ubiquitous ischyrocerid, is recognized by the outer ramus of 

 uropod 3 bearing a distally hooked, basally immersed spine, with 

 2 (occasionally 1 or 3) sharp, flat, asymmetrically triangular, slightly 

 reverted scales proximally adjacent to the distal spine. Other is- 

 chyrocerids may bear the spine but those so having also bear scales 

 (denticles, teeth, cusps) which are less flattened, not reverted, much 

 smaller, blunter, and more numerous than those of J. falcata. 

 Although Jassa falcata is well known to amphipodan taxonomists 

 because of its extreme antennal and gnathopodal polymorphism 

 (see Sexton and Reid, 1951), a new kind with unusually slender 



280-102 0-69— 3 



