NO. 9 MARINE INVERTEBRATES, ALASKA — MacGINITIE I55 



female was carrying young on August 30, 1949, and another con- 

 tained eggs in early stages of development. 



Two species of Pleurogonium, represented by a single specimen 

 each, were taken at 120 and 216 feet. 



The parasitic Phryxiis ahdominalis (Kroyer) was found on the 

 shrimp Eualiis gainiardi (20 females and i male) and on Spirontocaris 

 phippsi (i male). About 5 percent of the Eualus taken from 215 

 feet were parasitized by this isopod. Immature specimens of the 

 isopod were taken in August, October, and February, and females 

 with eggs (yellow to dark yellow) on October 10 and 14, 1949. 



Seven species of shrimps that are common hosts of Phryxus ah- 

 dominalis were collected at Point Barrow, but only two of these were 

 found parasitized, perhaps in some instances because too few speci- 

 mens were collected. Stephensen (1943c) reports that the common- 

 est host in east Greenland was Lebbius polaris and that only a few 

 were found on Eualus gaimardi, but that the latter species was the 

 common host in Iceland (1937a). This isopod is a circumpolar 

 species but has not been recorded previously from Point Barrow. 



Order AMPHIPODA 



It would be impossible to overestimate the importance of amphi- 

 pods in the Point Barrow fauna. They occur everywhere — in the 

 plankton, and in the gravel, mud, and rubble zones. They are nu- 

 merous, both as to species and individuals. That veritable swarms 

 occur in the plankton is evidenced by the great numbers that were 

 frequently washed ashore during storms (see below under Themisto 

 libellida and Melita jonnosa). They form an important source of 

 food for various fishes, for the bearded seals, and for many of the 

 invertebrate forms such as ctenophores, jellyfishes, chaetognaths, and 

 even other amphipods. Great numbers of the smaller Apherusa glaci- 

 alis occur on the undersides of ice floes and cakes, from which the 

 bearded seal can sweep them with its whiskers. On August 29, 1948, 

 great swarms of this amphipod would dart away from the undersides 

 of ice cakes when the latter were kicked. 



With at least three species of amphipods occurring in such vast num- 

 bers that seals can grow and thrive on them, it would seem that they 

 should form a source of food for military personnel forced to abandon 

 ship or make a forced landing. Apherusa glacialis could be gathered 

 with nets from the swarms that dart away when an ice cake is dis- 

 turbed. Further research on the natural history of this group through- 

 out the year could undoubtedly furnish information on ways and 



