Proteocephalus filicollis(Rudolphi, 1802) andProteocephalus ambiguus(Dujardin, 1845), Two Hitherto Confused Species of Cestodes

Abstract

Several kinds of data were collected from worms belonging to the genusProteocephalus, living in the intestines ofPygosteus pungitiusandGasterosteus aculeatus.a. Morphological data. When we compare the morphological characteristics of worms from the two hosts we find small differences in those characteristics commonly used in the descriptions of species of the genusProteocephalus. Regularly differences of the same magnitude are used to separate species.b. Experimental infections show that a high degree of host specificity exists in worms from the two hosts. It is impossible to cultivate worms originally coming from one host species in the intestine of the other. These experimental infections were carried out either by feeding intermediate hosts carrying plerocercoids to fishes free of infection, or by collecting worms from the intestine of one fish and introducing them into the intestine of another fish.Experimental infections of alien hosts failed whereas infections of the proper host, carried out as controls, always were successful.c. Mixed populations ofGasterosteusandPygosteusliving in a small closed canal system gave additional data indicating the existence of a high degree of host specificity. Throughout the yearGasterosteusshowed no infection at all whereasPygosteuswas “normally” infested.d. Monthly dissections ofPygosteusshowed that inProteocephalusliving in this fish species no seasonal cycle exists similar to that found by Hopkins inProteocephalusfromGasterosteus. The stages of development ofProteocephaluscollected during the dissections ofGasterosteuscorrespond with Hopkins' seasonal cycle.e. As a result of these observations it is proposed to consider the worms fromPygosteusas belonging to a distinct species. Since Dujardin was the first to describe worms belonging to the genusProteocephalusand living in the intestine ofPygosteusasProteocephalus ambiguus(Dujardin, 1845) this obviously ought to be the name of the species involved. The use of the nameP. filicollis(Rudolphi, 1802) is restricted to material fromGasterosteus.