Rhinebothriidae Euzet, 1953

Ruhnke, Timothy R., Caira, Janine N. & Cox, Allison, 2015, The cestode order Rhinebothriidea no longer family-less: A molecular phylogenetic investigation with erection of two new families and description of eight new species of Anthocephalum, Zootaxa 3904 (1), pp. 51-81 : 75

Rhinebothriidae Euzet, 1953

Diagnosis. Scolex with 4 bothridia; bothridia each with 1 or 2 columns of regular, facial loculi; with or without marginal loculi; locular columns extending throughout majority of length of bothridia; apical sucker and conspicuous anterior/posterior orientation of bothridia lacking; myzorhynchus lacking in adult stage. Postvaginal testes lacking (except in Rhabdotobothrium and Rhodobothrium ). Vitelline follicles not interrupted by ovary. Parasites of Myliobatiformes , Rajiformes , and Rhinopristiformes (sensu Naylor et al. 2012a).

Type genus. Rhinebothrium Linton, 1889 . Additional genera: Rhabdotobothrium Euzet, 1953 , Rhinebothroides Mayes, Brooks & Thorson, 1981 , Rhodobothrium Linton, 1889 , Scalithrium Ball, Neifar & Euzet, 2003 , Spongiobothrium Linton, 1889 ; possibly also Crassuseptum Eyring, Healy & Reyda, 2012 and Biotobothrium Tan, Zhou & Yang, 2009 but placement of these two genera in this family remains to be confirmed pending further molecular, and in the latter case, also morphological work.

Remarks. The subfamily Rhinebothriinae was established by Euzet (1953b) as an element of his proposed new classification of the Tetraphyllidea . At that time the subfamily included only Rhinebothrium and was characterized by its lack of an adult myzorhynchus and possession of bothridia that were “cloisonnées” (i.e., loculated). His subsequent (1994) diagnosis was fully consistent with his original concept of the subfamily. While the latter two features still serve to characterize members of this taxon, which henceforth should be known as the Rhinebothriidae in recognition of its elevation to family, we have expanded Euzet’s (1994) diagnosis to allow its members to be distinguished from the novel families established below that also bear facial loculi on their bothridia. The revised diagnosis also serves to accommodate genera not originally assigned to the subfamily by Euzet. This family is readily distinguished from all other families of rhinebothriideans in lacking bothridial apical suckers and also thus in lacking a definitive anterior/posterior orientation of the bothridia. That is not to say it is not possible to distinguish one end of a bothridium from the other for some species exhibit one loculus at one end and two at the other. It is just that without additional information it is not clear which end represents the anterior.

The results of our molecular analyses are fully consistent with those of Healy et al. (2009) in suggesting that Rhodobothrium has close affinities with taxa now considered to belong in the Rhinebothriidae . However controversy remains regarding the exact configuration of its distal bothridial surfaces. The scanning electron micrograph provided by Healy et al. (2009; fig. 13) shows evidence of small marginal loculi but little evidence of facial loculi. In contrast, both Euzet (1959) and Campbell and Carvajal (1979) illustrated irregular facial loculi. We suspect that facial loculi are in fact present in species of Rhodobothrium , but are only weakly muscular. Nonetheless, the morphology of members of this genus requires additional investigation in light of its placement in the Rhinebothriidae here.

We consider the monotypic Biotobothrium to be a provisional member of the Rhinebothriidae . This appears to be the most appropriate family placement for this genus based on its proglottid anatomy and possession of bothridia that do not exhibit apical suckers or a clear anterior/posterior orientation. However, the locular configuration of this species as described by Tan et al. (2009) is not fully consistent with the diagnosis of Rhinebothriidae presented here. Of most concern is that, rather than possessing one to two columns of loculi extending essentially throughout its length, this taxon was described as bearing five complete facial loculi arranged in one apical and two symmetrical pairs. It would be interesting to explore the family-level placement of this taxon using molecular data, and also to more fully characterize the configuration of the facial loculi in this taxon. Morphologically, Crassuseptum is consistent with the diagnosis of the Rhinebothriidae presented here, however it would also be interesting to explore this placement further using molecular data.