128 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28 



fathoms. The Point Barrow specimens extend the range of this species 

 to the western Arctic. 



Phylum CHAETOGNATHA 



Three species of arrow worms were taken, the most abundant being 

 Sagitta elegans Verrill. Since only surface plankton tows were taken, 

 there is a probability that the other two species are more abundant 

 than the haul would indicate. The writer is indebted to Dr. E. Lowe 

 Pierce for identifying this group. 



Sagitta elegans Verrill (probably var. arctica Aurivillius, the form 

 commonly found in Arctic waters) is exceedingly abundant at times 

 at Point Barrow. During the middle of July 1948 plankton tows 

 near shore brought in thousands of individuals 13 to 27 mm. in length. 

 These had immature gonads. Some 28-mm. specimens taken on 

 September 27, 1948, had long, slender ovaries and visible testes ; 

 others had very small ovaries. Dunbar (1941b) discusses the breed- 

 ing cycle of this species. 



In July, when the ice was melting rapidly, Sagitta survived when 

 the salinity of the surface water was only 18.12 to 15.22 parts per 

 thousand, but on July 16, 1948, when the salinity dropped from 15.22 

 to 5.81 between 9 a.m. and 4:30 p.m., untold millions were killed. 



Living Sagitta are caught and eaten by ctenophores, jelly fishes, and 

 hydromedusae. Those that fall to the bottom are soon devoured by 

 amphipods. 



Collection records for this species were made from September 9, 

 1949, to July 13, 1950, collections from January through June being 

 made by vertical plankton tows through holes in the ice. During 

 February and until late in March (for 6 tows), no Sagitta were 

 brought in, but they were taken throughout the remainder of the 

 winter season and became abundant in June. A few specimens taken 

 on June 20, 1950, were 11 mm. long and others were between 22 

 and 25 mm. long, indicating two age groups. 



On September 2"/, 1948, two specimens of Sagitta maxima ? 

 (Conant) 50 mm. in length were taken with a dip net from an ice 

 cake grounded near shore. A strong offshore wind was blowing the 

 surface water seaward and the deeper water was upwelling. 



Also on that same date, eight specimens of Eukrohnia hamata 

 (Mobius) were taken in the same manner as the above species. These 

 were about 40 mm. long, with well-developed testes and long ovaries 

 containing well-developed eggs. Two of the specimens were carrying 

 young in a marsupium formed by folding the posterior lateral fins 



