NO. 9 MARINE INVERTEBRATES, ALASKA — MacGINITIE I47 



The mud-dwelling Myriotrochus rinki Steenstrup was taken at 

 depths of 20 to 70 feet, and on several occasions hundreds were 

 washed ashore during storms. This species ingests large quantities 

 of mud for its contained detritus. Eggs appeared mature on Au- 

 gust 10, 1950. In Greenland this species harbors a commensal snail 

 Entocolax liidwigi within its cloaca. Although many specimens were 

 examined, no snails were found in the Point Barrow Myriotrochus. 



Psolus fabricii' (Diiben and Koren) was dredged from depths of 

 120 to 453 feet. As with the sea urchin, either very few or else large 

 numbers of this animal were dredged. For example, ii8 were taken 

 at 125 feet, and 86 at 130 feet, 86 at 120 feet, and 170 at no feet on 

 September 15, 1948. This is a detritus feeder. Spawning was not 

 observed, nor were the gonads examined. The measurements of 

 juveniles collected over a period of 2.5 months suggest that the spe- 

 cies must spawn over a considerable period of time. 



Phylum ARTHROPODA 

 Class CRUSTACEA 



The crustaceans form a very important part of the fauna at Point 

 Barrow for they are extremely abundant both as to species and indi- 

 viduals. They include pelagic and bottom-dwelling forms, both of 

 which supply food for other animals. 



Order OSTRACODA 



The writer is indebted to Dr. Willis L. Tressler for supplying distri- 

 bution data and identifying the members of this group, which con- 

 sisted of 61 individuals and 5 species, each from a different genus. 

 With the exception of those found on an amphipod, the greatest 

 number — 21 individuals, representing four of the genera and species — 

 came from the station at 741 feet. This suggests that still deeper 

 dredging might yield a greater population of ostracods than were 

 found in the present investigation. Even at shallower depths, if special 

 methods of collecting were employed, the yield in individuals at least, 

 and probably in species, would be greater. Only 4 species of ostracods 

 have been taken on the east coast of Greenland, as compared with 

 about 50 from the west coast. This discrepancy in number of species 

 may be due largely to differences in methods and intensity of collect- 

 ing and perhaps to differences in sorting methods. Such small animals 

 are easily overlooked. 



A total of 19 specimens of the commonest and largest species at 



