Dasyrhynchus giganteus; tentacle of Halsiorhynchus macrocephalus; Otobothrium mugilis; D. giganteus in brain cavity of Caranx hippos (top); misc. defintive nad intermedate hosts. (Photos courtesy of K. Jensen)

MORPHOLOGY: Scolex usually with 4 eversible tentacles at its apex; tentacles generally bearing a complex array of diverse hooks used for attachment to the mucosa of the gastrointestinal tract. Proglottids usually with 1 set of male and female reproductive organs. Genital pores lateral or sub-lateral. Ovary tetra-lobed in cross section, uterus saccular; uterine pore may be present. Vagina usually entering genital atrium posterior to, but occasionally anterior to, cirrus; vagina and cirrus frequently unite in cirrus-sac to form an hermaphroditic duct. Vitelline follicles usually surround the medulla, frequently obscuring all internal features.

DIVERSITY: About 280 species arranged in 70 genera. Second-most diverse group of elasmobranch cestodes. However, only a small proportion of the currently recognized ~1,200 elasmobranch species have been examined for cestodes thus, many species remain to be described. Familial classification is controversial; ~15 families are currently recognized.

PHYLOGENETIC RELATIONSHIPS: The systematics of the order are far from resolved; several genera inquirenda and a large number of species inquirendae remain to be treated. The classification of Campbell & Beveridge (1994) follows Dollfus (1942) in emphasizing tentacular armature; whereas, Palm (1997, 2004) considered armature to be of secondary importance. A preliminary cladistic analysis (Beveridge et al., 1999) provided some support for both classifications, but also suggested novel combinations. The order is considered monophyletic based on morphological and molecular data (Palm et al, 2009; Olson et al, 2010).  The order is currently divided into two sub-orders, the Trypanobatoidea and Trypanoselachoidea (Olson et al., 2010).

DEFINITIVE HOSTS: Elasmobranchs.

SITE IN DEFINITIVE HOST: Most species are found in the spiral intestine, with a few occurring in the stomach and gall bladder.

GEOGRAPHIC DISTRIBUTION: Cosmopolitan.

LIFE-CYCLES: Larval stages (plerocerci or post larvae) are common inhabitants of the body cavities of teleosts, crustaceans or, rarely, reptiles. Complete ife-cycles of few species are known. Currently known life-cycles involve either development of a procercoid in a copepod and a plerocercus in a teleost, or, alternatively, development of a plerocercus in the first intermediate crustacean host. In both cases completion of the life-cycle occurs in an elasmobranch host.

Selected References:

Dollfus, R.-Ph. 1942. Etudes critiques sur les tétrarhynques du Museum de Paris. Archives du Muséum National d' Histoire Naturelle, Paris 19: 1-466. PDF

Campbell, R. A. and I. Beveridge 1994. Order Trypanorhyncha Diesing, 1863. pp. 51-148. In Khalil, L. F., Jones, A., Bray, R. A. (Eds.) Keys to the cestode parasites of vertebrates. CAB International, Wallingford, U.K. PDF

Palm, H. 1997. An alternative classification of the trypanorhynch cestodes considering the tentacular armature as being of limited importance. Systematic Parasitology 37: 81-92.

Beveridge, I. and M. K. Jones 2002. Diversity and biogeographical relationships of the Australian cestode fauna. International Journal for Parasitology 32: 343-351.

Palm, H. 2004. The Trypanorhyncha Diesing, 1863. PKSPL-IPB Press, Bogor, 709pp.

Palm, H.W., A. Waeschenbach, P. D. Olson, and D. T. J. Littlewood 2009. Molecular phylogeny an evolution of the Trypanorhyncha Diesing, 1863 (Platyhelminthes: Cestoda) Molecular Phylogenetics and Evolution 52: 351-367.

Olson, P. D., J. N. Caira, K. Jensen, R. M. Overstreet, H. Palm, and I. Beveridge. 2010. Evolution of the trypanorhynch tapeworms: Parasite phylogeny supports independent lineages of sharks and rays. International Journal for Parasitology 40: 223-242.

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