On the genusDinobothriumvan Beneden (Cestoda), with a description of two new species from sharks, and a note onMonorygmasp. from the electric ray

Publisher Website
Google Scholar
Abstract
A new species of the giant phyllobothriid genusDinobothrium(D. keilinin.sp.) is described from the blue shark (Carcharinus glaucus); it is compared withD. planumLinton, found for the first time from British waters, in the basking shark (Cetorhinus maximus), and the structure of both is discussed in relation to that of the genotype,D. septariavan Beneden. A fourth species,D. paciferumn.sp., also from the basking shark, is described, and though only a tenth the size of the other species, it shares most of their diagnostic scolex characters. It has eight true suckers above the four pendent bothria: inD. planumthere are four true suckers and four pseudo-suckers, while inD. keilinithere are only four true suckers, andD. septariais said to have four pseudo-suckers alone. The nomenclature of the older species is revised, and the genus redefined.Attention is directed to the adaptations in these large cestodes which facilitate interchange with the substratum: the development of lateral furrows through which the main excretory canals open to the exterior. There is also a ventral furrow, which in the nascent segments is an open cleft: this accommodates the growing uterus and permits a protracted gravid phase of the proglottidesin situ. The effect is of five longitudinal hinges, which allow of considerable lateral expansion of the thick-walled strobilus. The smallerD. paciferumlacks these modifications, and the cylindrical segments are apparently detached in the gravid state. An explanation is offered for the conflicting accounts of the lateral extent of the vitellaria in this genus: there is a lateral contraction of the ventral vitelline reticulum as the ovarian phase waxes. InD. paciferumthe vitellaria completely encircle the proglottis at the inception of the ovarian phase.Notes are given on the selachiàn hosts examined, their food and the other parasites present. The relationships ofDinobothriumto other phyllobothriid genera and toTetrabothriusare discussed.In one electric ray,Torpedo nobiliana, a single immature strobilus of another kind of phyllobothriid was found; it is probably a new species ofMonorygma, though it has slight resemblances toCalyptrobothrium—a genus characteristic of electric rays. The boat-shaped bothria are held at an angle from the scolex by contractile buttress-like wings, and at their proximal end there is a relatively large and complex sucker. Affinities with related genera are discussed and the nomenclature ofMonorygma angusta(Linton) is emended.
Keywords