JUVENILE NEMATODES (ECHINOCEPHALUS PSEUDOUNCINATUS) IN THE GONADS OF SEA URCHINS (CENTROSTEPHANUS CORONATUS) AND THEIR EFFECT ON HOST GAMETOGENESIS

¹ W. M. Keck Laboratories, California Institute of Technology, Pasadena, California 91109
² Department of Nematology, University of California, Davis, California 95616

1. The juvenile phase of the nematode Echinocephalus pseudouncinatus occurs commonly in the gonads of the sea urchin Centrostephanus coronatus off Southern California. The gonads of about 78% of the urchins in Big Fisherman's Cove, Santa Catalina Island, were heavily infected with the juveniles. About 40% of the urchins at Pin Rock in Catalina Harbor, Santa Catalina Island, and at Whistler's Reef off Corona del Mar on the mainland coast of California were infected, although the infection was usually not as severe as in Big Fisherman's Cove. A juvenile, probably of E. psuedouncinatus, also was found in gonads of C. coronatus collected from Bahia Tortola off west-central Baja California. Although juveniles of E. pseudouncinatus also occur commonly in the foot of pink abalones, they only rarely infect other species of sea urchins in Southern California.

2. The California horned shark Heterodontus francisci seems a likely host of the adult phase of E. pseudouncinatus. However, when specimens of the horned shark were examined, adult specimens of Echinocephalus were found which do not seem to be the same species as our juvenile specimens.

3. The juvenile nematodes were encysted mainly in the spaces (perihemal or hemal) between the perivisceral coelomic epithelium and the germinal epithelium of the Centrostephanus gonad. Large juveniles filled the host gonadal tubule and bulged into the perivisceral coelom. Host gametogenesis was suppressed in the infected gonadal tubule, especially in the oral parts of such tubules. Gametogenesis in adjacent tubules did not seem affected. When the juveniles were in major tubules of the host gonad, severe suppression of host gametogenesis occurred in the oral parts of the gonad. It is suggested that encysted juveniles block the passage through the gonadal tubules of some hormonal substance that regulates urchin gametogenesis.