NO. 9 MARINE INVERTEBRATES, ALASKA — MacGINITIE II3 



13, 1950, with well-developed buds is an indication of earlier repro- 

 duction of the hydroid. 



Larval ctenophores were present up to September 30, 1949, and ap- 

 peared again on February 25, 1950, and became increasingly abundant 

 from then on. Fragments of ctenophores were found on November 

 10, 1949, and small ctenophores and fragments on January 25, 1950, 

 showing that these forms were not entirely absent. 



The giant trochophores that were present throughout the month 

 of June suggested that they might be those of the echiuroid Hamingia 

 arctica, for the latter produces giant eggs (see phylum Echiuroidea, 

 under "Discussion of Animals by Phyla"). 



Larval polychaetes and small worms were present all during the 

 winter. The main sexual activity and egg-bearing stages of several 

 of the polychaetes occur in winter. 



Copepods were present throughout the winter, ranging from com- 

 mon to abundant to exceedingly abundant. Nauplii were much less 

 common during the winter, not becoming abundant until about May 

 17, 1950. Although never abundant, other crustacean larvae of vari- 

 ous kinds were present throughout the winter. 



It is an interesting fact that although veliger larvae were never 

 abundant as compared with other forms, they were present through- 

 out the winter. Certain gastropods must lay eggs at various times 

 during the winter or else the larvae spend a long pelagic life. Most 

 of the tgg capsules that were dredged or washed ashore during the 

 open season contained young snails at some time, but there were sev- 

 eral kinds that contained only eggs and too few were found to deter- 

 mine whether the eggs hatched as swimming larvae or as young snails. 

 It is possible that in some species the eggs hatched as swimming larvae 

 that escaped from the capsules without further development and that 

 these were the veligers found in the winter plankton. 



That invertebrate eggs and fish eggs begin to be common to abun- 

 dant in June is another proof that certain animals either carry on as 

 usual during the winter or produce eggs from oil stored during the 

 open season. 



PARASITES AND COMMENSALS 



It is unfortunate that more could not be learned of the parasitic 

 and commensal relationships of the animals collected, for these rela- 

 tionships form such an interesting and important part of the knowl- 

 edge of a fauna. When animals must be obtained by dredging (rather 

 than by digging them from mudflats or sand or by finding them 

 among or under rocks ) , the determination of commensal relationships 

 is difficult and sometimes impossible. 



