Three new genera and species of tapeworms from the longnose sawshark, Pristiophorus cirratus, with comments on their modes of attachment to the spiral intestine

Abstract

The spiral intestines of 18 specimens of the longnose sawshark Pristiophorus cirratus, collected from southeastern Australia, were examined for parasites. Three new genera and species of tetraphyllidean tapeworms belonging to the Phyllobothriinae within the Phyllobothriidae were discovered as a result of these necropsies. Flexibothrium ruhnkei n. g., n. sp. differs from all other phyllobothriine tapeworms in its possession of bothridia that each bear an apical sucker and a posterior margin that is flexed anteriorly and fused along the median line of the distal bothridial surface, forming 2 essentially open-faced grooves. Light and scanning electron microscopy of worms attached to the mucosal surface suggest that this species uses the open-faced bothridial grooves, the outermost surface of the anteriorly flexed portion of each bothridium, and the interbothridial surfaces to grasp up to a total of 16 mucosal villi and/or ridges. Cardiobothrium beveridgei n. g., n. sp. is unique among the phyllobothriids in its possession of bothridia each with an apical sucker, marginal loculi, and 4 facial loculi arranged in 2 tandem pairs. This taxon is provisionally placed within the Phyllobothriinae, and the subfamilial diagnosis is emended to include species with facial loculi. Examination of specimens fixed in situ and then removed from the mucosal surface suggests that this species uses the larger, posterior pair of facial loculi of each bothridium to grasp the tips of a pair of adjacent villi in order to attach to the mucosal surface. Bibursibothrium gouldeni n. g., n. sp. also appears to belong in the Phyllobothriinae. Within this subfamily it most closely resembles species of Marsupiobothrium in its possession of pouchlike bothridia. However, it conspicuously differs from species in this genus in that its bothridial pouches are subdivided internally into 2 distinct compartments. Cross sections of individuals of this taxon attached to the mucosal surface indicate that each bothridium is used to grasp 2 adjacent mucosal elements such that the scolex has the ability to attach to up to a total of 8 villi and/or ridges. The discovery of 3 new genera of tapeworms from this host species is not unexpected given the high degree of host specificity generally exhibited by the phyllobothriids, and that this is the first report of tapeworms from a shark of the order Pristiophoriformes.