The Effect of Parasitism by an Entoniscid on the Secondary Sex Characters of Pagurus longicarpus

Abstract

The common hermit crab Pagurus longicarpus Say is parasitized at Woods Hole by two species of EPICARIDEA (a suborder of isopod crustaceans). A bopyrid, Stegophryxus hyptius Thompson, occurs attached to the abdomen and an entoniscid, Paguritherium alatum Reinhard, is found within the haemocoele. Simultaneous parasitism by both the bopyrid and the entoniscid is, however, of rare occurrence. Stegophryxus causes no external modifications of the host, neither does it effect any marked reduction of the gonads. Paguritherium, on the other hand, brings about complete castration of female hosts and more or less complete atrophy of the male gonads. The pleopods of infested males are unmodified, but those of infested female crabs, while normal in number, resemble the male type more than they do the type characteristic of normal adult females. The effects of RHIZOCEPHALA and EPICARIDEA on the secondary sex characters of hermit crabs as reported in the literature fall into four categories: I. Male pleopods modified; female pleopods unaffected. By RHIZOCEPHALA: Pagurus cuanenis (Nilsson-Cantell, 1926) and Pagurus prideauxii' (Potts, 1906; Baffoni, 1947). By EPICARIDEA: Pagurus bernhardus (Giard, 1887; Bonnier, 1900) and Pagurus prideauxii (Baffoni, 1947). II. Male and female pleopods both modified. By RHIZOCEPHALA: Pagurus meticulosus (Potts, 1906) and Pagurus samuelis (Shiino, 1931). III. Male pleopods unaffected; female pleopods modified. By RHIZOCEPHALA: Pagurus bernhardus (Giard, 1887; Guerin-Ganivet, 1911). IV. Male and female pleopods both unaffected. By RHIZOCEPHALA: Anapagurus chiroacanthus (Nilsson-Cantell, 1926) ; Pagurus pubescens (Reinhard, 1942). By EPICARIDEA: Pagurus longicarpus (Thompson, 1901). No case has been reported in which a female pagurid manifested alterations in its secondary sex characters under the influence of an epicaridean parasite and only a few instances, based on scarce material, where the presence of a rhizocephalan parasite affected the external characters of the female alone. It was therefore thought worth while to study the female pagurids infested with Paguritherium and analyze as completely as possible the modifications of the pleopods with respect to the size of the host, the amount of deviation from the normal and the precise nature of the changes to discover whether the alterations were a retention of the juvenile condition, a state of female intersexuality, or some other phenomenon.