FlGlRE 7. — Lagenophrys encysted on g:ills of blue crab 

 (X 70). 



active and encysted forms of the parasite in 

 Kreat detail. He also cultured the orj^anism. 

 Aiioplirjis apparently invests large numbers of 

 host amebocytes, and multiplies until the blood 

 becomes a dense "soup" of motile parasites. 

 The di.sease, though often fatal once infection 

 occurred, was relatively rare on the French 

 coast. Experimental infections, achieved by in- 

 jecting the ciliates, killed crabs in 2 to 7 days. 

 Certain individual crabs seemed resistant to 

 infection, but no antibody response was de- 

 tected. Effects on the parasites included inhibi- 

 tion of reproduction, immobilization, and even- 

 tual death. 



Discuses (.nused by Helminths 



Helminth infest.itions include larval trema- 

 todes and cestodes, as well as nemerteans and 

 leeches. 



Trematode metacercariae are common in sev- 

 eral species of crabs. Larvae of Microphallus 



(Spelotrema) nicoUi, encysted in body muscles 

 of blue crabs, were described by Cable and 

 Hunninen (1940). Adult trematodes occur in 

 young herring gulls, Larm argentatus, and spo- 

 rocyst generations in the snail Biftium alfcrna- 

 tum (Say). A haplosporidan hyperparasite, 

 Urosporidium crescens [De Turk], has been 

 found in metacercariae of MicrophnlUis nicolli 

 from blue crabs caught in North Carolina 

 (Anonymous, 1940). One third of the crabs ex- 

 amined contiiined metacercariae, but the extent 

 of hyperparasitization was not determined. The 

 host metacercarial ti.ssue was often completely 

 destroyed, leaving little more than a sack of 

 protozoan spores. Invasion by rronporidiian 

 was thought to occur before encystment of cer- 

 cariae. Masses of dark pigmented spores in the 

 destroyed metacercaria i)roduce a black spot, 

 which has led to the application of the descrip- 

 tive colloquial term "pepper crab" to hyperpar- 

 asitized individuals. "Pepper spots" occur most 

 commonly in fat bodies, digestive gland, and 

 mu.scles of the crab. 



Metacercariae of Microphallus (Spclatrcnia) 

 carciui Lebour were reported from the hepato- 

 pancre.is of green crabs from the English 

 Channel (Guyenot et al. 1925), the Mediter- 

 ranean (Timon-David, 1949), and elsewhere. 

 Hyperparasitization of metacercariae by the 

 microsporidan A'asrw« (Plistophora) spelo- 

 trcmac was reported by Guyenot et al. Meta- 

 cercariae of Microphallus similis (Jagerskiold) 

 occur in the hepatopancreas of the green crab 

 of the western North Atlantic (Stunkard, 

 1957). Young green crabs were killed in 10 

 to 20 days by massive experimental exposui'e 

 to cercariae of M. similis. 



Larval diphyllidean cestodes (Echivohoth- 

 riiiDi nffine Diesing) have been reported by 

 Dollfus (19G4a, 1964b) from green crabs sam- 

 pled at Roscoff on the coast of France. 



Juvenile nemerteans, Carciiionemcrtcs carci- 

 nophila (KoUiker), encyst on the gills of the 

 blue crab. After the female crab spawns, the 

 worms excyst and migrate to the egg ma.ss, 

 where they mature, lay eggs, then return to the 

 gills (Davis, 1965). Hargis (1959) h.is cited 

 this parasite as an indicator of host physiology, 

 since Hopkins (1947) pointed out that in- 

 creased size and more noticeable color were 

 characteristic of reencysted worms after the 



354 



U.S. FISH AND WII DIIFF. SERVICE 



