Historical Chaos among Tetrabothriideans (Eucestoda) of Odontocetes (Artiodactyla)—Revising Generic Taxonomy and Species Diversity for Cestodes among Oceanic Dolphins

Authors

• Eric P. Hoberg, University of New MexicoFollow
• Kaylen Marie Soudachanh, University of New Mexico
• Robert L. Rausch, University of Washington

ORCID IDs

Hoberg 0000-0003-0819-7437

Date of this Version

9-17-2026

Document Type

Article

Citation

MANTER: Journal of Parasite Biodiversity, Number 38, September 17, 2026

doi: 10.32873/unl.dc.manter38

Comments

Copyright © 2026, the authors. Open access

License: CC BY-NC-SA 4.0

Abstract

Explorations over the past 150 years that have defined the diversity and structure of the tetrabothriidean cestode fauna among Odontocete cetaceans (Artiodactyla) are summarized and reviewed. Persistent errors in interpretation of comparative morphological characters, inconsistent taxonomic decisions, and an understanding of generic-level and species diversity are addressed. We outline a revision of the Tetrabothriidea, which now encompasses 8 genera. Prosthecocotyle is resurrected from synonymy with Tetrabothrius, and Cetaceobothridius n. gen is proposed. A clear basis is outlined for differentiation of generic and species diversity among Cetaceobothridius, Priapocephalus, Prosthecocotyle, Strobilocephalus, Tetrabothrius, and Trigonocotyle that constitute the tetrabothriidean fauna of odontocetes; species of Chaetophallus are known in seabirds, whereas Anophryocephalus occurs among pinnipeds. An extensive series of original line drawings and micrographs prepared from validated specimens in global museum archives are presented to demonstrate the extent of inter- and intraspecific variation in structural diagnostic attributes for respective genera and species. There are 18 species of tetrabothriideans in 6 genera, with extensive realized host and oceanographic ranges, known from 36 of 64 (56%) species of odontocetes documented to have been examined for helminths. An assemblage of tetrabothriideans occurs primarily among species of the Delphinidae (basal Delphinidae, Delphininae, Lissodelphininae, Globicephalinae), Phocoenidae, Physeteridae, and Ziphiidae. Specifically, we resurrect Prosthecocotyle relative to Tetrabothrius and Trigonocotyle. Emended generic diagnoses are presented, focusing on structural attributes of scolices, genital atria, and organs of the male and female genital complex. The historical status of Tetrabothrius forsteri is examined, establishing morphological limits with a redescription and validation under Prosthecocotyle forsteri based on the original type series. Recognized diversity for Prosthecocotyle includes 6 species, P. forsteri (type), P. dalli n. comb, P. hobergi n. comb., and Prosthecocotyle merche n. sp., n. comb. [of 2 Fernández et al. (2004)] with emended descriptions; further, 2 previously unrecognized species are proposed and characterized. Problems with P. forsteri, and the possibility of a putative cryptic complex, indicate the need to reevaluate host and oceanographic records based on archived specimens with validated authoritative identification. Secondarily, it becomes requisite that a comprehensive foundation of sequence/genomic data be assembled that is directly linked to definitions of diversity emanating from principles of comparative morphology and archived specimens from oceanographically dispersed field-based collections. Following resurrection of Prosthecocotyle, Tetrabothrius innominatus represents the sole species of the genus in odontocetes of small to medium body size. Trigonocotyle includes 5 species, with the resurrection and redescription of Tr. lintoni (and suppression of Tr. globicephalae as a synonym), consideration of Tr. prudhoei, Tr. sexitesticulae, Tr. spasskyi and description of a previously unknown species. Additional comments are presented regarding Priapocephalus, Tetrabothrius, and Strobilocephalus. Realized host ranges for a tetrabothriidean fauna are extensive against a backdrop of considerable fundamental fitness space (FFS) in marine systems. Overall, the fauna is widespread, demonstrating a broad heterogenous oceanographic range. Biological and physical drivers and determinants of diversity and host range in this marine assemblage are examined. Lifecycles and circulation for tetrabothriideans remain unresolved and enigmatic. Tetrabothriideans are strictly marine, and previous research has suggested a three-host cycle involving pelagic crustaceans (copepods, euphausiids, and other micro- to meso- and macrozooplankters), cephalopods (squid and cuttlefish), and (or) teleosts (myctophids and other mesopelagic fishes; other shoaling marine forage fishes such as capelin or sandlance) as intermediate and paratenic hosts and homeotherms as definitive hosts. Species diversity, host range, and oceanographic distributions for cestodes, along with ecological dynamics for foraging, suggest a pathway for further explorations of circulation in marine systems. Squids and mesopelagic fishes may be common denominators as intermediate and paratenic hosts in tetrabothriidean lifecycles and transmission among odontocetes. Such observations may contribute to targeting attempts to elucidate tetrabothriidean cycles among marine prey guilds, food webs, and regions. Realized host range for tetrabothriideans is established within FFS that defines capacity and compatibility for diverse assemblages of zooplanktonic and nektonic invertebrates linked to transmission, circulation, and persistence of the fauna in odontocetes. Processes of host colonization across temporal and spatial scales, reflecting the interaction of organismal capacity and ecological opportunity in changing environments, are consistent with the Stockholm Paradigm. The contours for host range are predicted to encompass most of the marine odontocete fauna. Intersecting with FFS, the broader dimensions of realized host range may be revealed through continuing survey of odontocetes and oceanographic regions with potential discovery of currently unrecognized associations or unknown tetrabothriideans. There is an urgency in articulating comprehensive views of diversity with accurate data for parasite and host identity along with oceanographic range in an arena of expanding and accelerating atmospheric warming and regimes of climate and oceanographic forcing that drive perturbations to marine ecosystems globally.