STUDIES ON THE LIFE HISTORY AND HOST-PARASITE RELATIONSHIP OF PELTOGASTER PAGURI

Abstract

Of 3,092 Pagurus pubescens examined, 13.7 per cent were found to be parasitized by Peltogaster paguri, the incidence of infestation being somewhat higher in female than in male crabs. Considerable biotic resistance on the part of the parasitized host is indicated by the small number of double and triple infestations. The external sac, which reaches sexual maturity in from 6 to 7 weeks after eruption, produces from 10,000 to 28,000 nauplii, and successive broods may follow one another at approximately 30 to 40 day intervals. The average size attained by adult Peltogasters is directly proportional to the size of the host, female crabs supporting, on the average, larger parasites than do the males. The age at which parasitism takes place depends on the relative size of the different host species, and is not necessarily related to the degree of host maturity. Peltogaster causes complete degeneration of the gonads in the female Pagurus pubescens but does not cause castration of the male. Secondary sexual characters are not appreciably modified.