no. 3613 TW o NEW CRUSTACEANS — BOWMAN AND KORNICKER 5 



collections from Lyttleton Harbor, New Zealand, Hansen (1905) 

 found Sphaeronellopsis littoralis in Sarsiella hispida but not in the 

 much more abundant Sarsiella hanseni. 



Effects of parasitism on the host. — We have observed no 

 differences between parasitized and nonparasitized ostracods in the 

 structure of the shell or the body and its appendages. As Hansen 

 (1897) has pointed out, choniostomatids apparently feed by piercing 

 the host's integument with pointed mandibles and sucking its blood 

 with the aid of the funnel-shaped mouth cone. The effect of this 

 feeding on the ostracod is unknown. The most serious effect of the 

 Sphaeronellopsis appears to be the inhibition of ovulation by the host. 

 Only 1 of the 23 parasitized female ostracods had laid its own eggs 

 in its marsupium. Conversely, the copepod seems to be deterred 

 from entering the marsupium of an ostracod that is incubating its 

 own eggs; 16 of the 17 ostracods with their own eggs in their marsupia 

 were not parasitized. 



These observations are similar to those of Hansen (1897), who 

 reported that in studying the 38 species of choniostomatids living 

 in crustacean marsupia, he found almost 160 cases of marsupia with 

 parasites and no host eggs, but only 6 cases wherein parasites and host 

 eggs occurred together. 



Egg mimicry in the Choniostomatidae. — The similarity in size of 

 Sphaeronellopsis ovisacs and the eggs of the ostracod host is more than 

 coincidental. While the individual Sphaeronellopsis eggs are much 

 smaller (diameter about .07 mm) than the ostracod eggs, they are 

 grouped into clusters of about 15 eggs; the diameter of the clusters 

 usually falls between .20 and .30 mm, about the same as that of the 

 ostracod eggs. This similarity in size clearly seems to be a case of egg 

 mimicry having adaptive value for the Sphaeronellopsis. The 3rd 

 thoracic legs of myodocopid ostracods are very flexible, adapted for 

 removing foreign particles from the interior of the valves and from the 

 eggs (Skogsberg, 1920, p. 88, ftn.). Individual copepod eggs pre- 

 sumably would be removed from the brood chamber by the cleaning 

 leg, but the copepod avoids this hazard by laying its eggs in groups 

 within sacs, each sac mimicking 1 of the ostracod eggs in size and shape. 

 Instead of being removed as a foreign particle, the Sphaeronellopsis 

 ovisac is retained within the brood chamber and cleaned by the host 

 with the same solicitude given to its own eggs. To a male ostracod, 

 however, an ostracod egg or a Sphaeronellopsis ovisac mimicking an 

 ostracod egg is a foreign particle and therefore is removed by the 

 cleaning leg. It is significant that in the few instances in which a 

 female Sphaeronellopsis was found in a male ostracod, no ovisacs 

 were present. 



