SOUTHERN OYSTER DRILL AS A PREDATOR 



81 



Table 4. — Comparison of stained and mounted sexually mature P. acanthus adults from several sources 



[All measurements are in mlUimeters] 



The essential features of Stunkard and Cable's 

 and Rees' life cycle accounts were collated and 

 summarized by Cooley (1957), who also compiled 

 lists of known hosts, infection sites in each host, 

 and localities where the parasite is endemic. 



To this host list should be added the ruddy 

 turnstone (Arenaria i. interpres), the natural 

 host in Hawaii, and noddy terns (Anom stoUdvs 

 pileatus Scopoli), sooty terns {Sterna fuscata 

 oahuensis Bloxam), wedgetailed shearwaters 

 {Pufiinus pad feus cuneatus Salvin), and domestic 

 ducks (Muscovy, Pekin), the last four being ex- 

 perimentally infectible when maintained on a diet 

 of squid (Oguri and Chu, 1955) ; also the laugh- 

 ing gull (/.. atriciUa), a natural host in Florida, 

 and the least tern (Sterna albifrons), an experi- 

 mental host (present study). 



619364 — 62 2 



Despite the number of studies of various aspects 

 of the life cycle of P. acanthus, apparently no one 

 has described the actions of the miracidium as it 

 attacks the drill. 



Invasion of the drill by Parorchis miracidia. — 

 Living miracidia are easily obtained by teasing 

 eggs from the uterus of the adult worm into sea 

 water. They hatch almost immediately. The 

 hatching process is well described by Rees (1940). 



The miracidium is a very rapid and active 

 swimmer. Its restless to and fro movements seem 

 without direction and contact with the drill ap- 

 pears to be accidental. However, a few observa- 

 tions cuggest that the parasite may be attracted 

 by tlie mucus secreted by the drill. 



Rees (1940) stated that the position of the 

 young first generation rediae in the digestive gland 



