COPULATION AND SEXUAL CONGRESS OF LEPTORHYNCHOIDES THECATUS (ACANTHOCEPHALA)

Pairs of the acanthocephalan Leptorhynchoides thecatus from laboratory infections were observed copulating at 21 days, 5 wk, and 12 wk posti nfection (PI) in green sunfish Lepomis cyanellus. Additionally, copula ting pairs of worms from natural infections were observed. In each ins tance of paired males and females, the male was in 1 pyloric cecum of the fish and the female in another. Each had its posterior end protrud ing into the intestinal lumen at the point from which the ceca arise. The completely extruded bursa of the male fully enclosed the posterior end of the female in a firm attachment. In 1 instance at 5 wk PI, 2 m ales were observed in copula. One male had its copulatory bursa comple tely retracted, and the copulatory bursa of the other male was positio ned just as though the mate were a female. Based on these and previous findings, it is concluded that male acanthocephalans mate indiscrimin ately and often throughout their lives. Habitation of ceca maximizes s exual congress because individuals often are positioned with their pos terior ends extending into the intestinal lumen within the small area from which ceca originate. Emigration to find a mate is unnecessary.