MARINE AMPHIPODA IN MICRONESIA — BARNARD 539 



relationship to several species of Eurysiheus. This relationship in- 

 volving gnathopods, head, and eyes further points to the artificiality 

 of the arrangement made by J. L. Barnard and the difficulty in separat- 

 ing several photid genera. The accessory flagellum is bi-articulate 

 whereas the genus Eurystheus has a 3+ articulate flagellum. No 

 species of Megamphopus, as listed by J. L. Barnard (1962a), has yet 

 been found in the Indo-Pacific and M. abbotti is apparently simply a 

 Eurystheus that has lost one more flagellar article. 



This species differs from Eurystheus semichelatus K, H. Barnard 

 (1957) and E. Una Kunkel (1910) by not having a distinctly semichelate 

 second gnathopodal palm; from E. crassipes Haswell (1880) by the 

 longer, narrower sixth article of gnathopod 2, bearing a nonexcavate 

 palm; from E. scissimanus K. H. Barnard (1925) by the lack of a 

 medial palmar excavation on gnathopod 2. It differs from E. minutus 

 Chevreux (1926) by the more elongated eyes, the narrower, more 

 elongated sixth article of gnathopod 2, and the slightly different 

 palmar configuration. 



Because of the eye structure this species is easily confused with 

 Eurystheus afer (Stebbing 1888) but the palm of the second gnathopod 

 in E. afer is oblique and article 6 is not as rectangular. 



Distribution: Ifaluk Atoll, Caroline Islands; Eniwetok Atoll, 

 Marshall Islands. 



Family Ampithoidae 



Key to Genera 



1. Mandible lacking palp Sunamphitoe 



Mandible bearing palp 2 



2. Antenna 1 lacking accessory flagellum 3 



Antenna 1 bearing accessory flagellum 6 



3. Gnathopod 1 larger and stouter than gnathopod 2 Exampithoe 



Gnathopod 1 smaller and more slender than gnathopod 2 4 



4. Gnathopods feeble, chelate Macropisthopus 



Gnathopods large, subchelate 5 



5. Article 6 of pereopods 3-5 widened apically Pleonexes 



Article 6 of pereopods 3-5 not widened apically Anipithoe 



6. Outer ramus of uropod 3 bearing 1 hook Amphithoides 



Outer ramus of uropod 3 bearing 2 hooks 7 



7. Gnathopod 1 larger than gnathopod 2 Paragrubia 



Gnathopod 1 smaller than gnathopod 2 Cymadusa 



According to this key, Ampithoe megaloprotopus Stebbing (1906, p. 

 633) should be transferred to Exampithoe. Amphitholina Ruffo was 

 transferred to the family Eophliantidae by Gurjanova (1958). 



768-792—65- 



