Hirudinella ventricosa (Pallas, 1774) Baird, 1853 represents a species complex based on ribosomal DNA Dana M. Calhoun • Stephen S. Curran • Eric E. Pulis • Jennifer M. Provaznik • James S. Franks Received: 30 October 2012 / Accepted: 14 August 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Digeneans in the genus Hirudinella de Blainville, 1828 (Hirudinellidae) from three species of pelagic fishes, Acanthocybium solandri (Cuvier), Makaira nigricans Lace ´pe `de and Thunnus albacares (Bonnaterre), and one benthic fish, Mulloidichthys martinicus (Cuvier), from the Gulf of Mexico are investigated using comparison of ribosomal DNA. Four species are identified based on molecular differ- ences: Hirudinella ventricosa (Pallas, 1774) Baird, 1853 from A. solandri, Hirudinella ahi Yamaguti, 1970 from T. albacares, and two unidentified but distinct species of Hirudinella, herein referred to as Hirudinella sp. A (from both M. nigricans and M. martinicus) and Hirudinella sp. B from M. nigri- cans. Additionally, H. ahi, based tentatively on morphological identification, is reported from Thun- nus thynnus (Linnaeus). This represents the first record of a hirudinellid from M. martinicus and the first record of H. ahi from T. thynnus. A phylogeny of some Hemiurata Skrjabin & Guschanskaja, 1954 using partial fragments of the 28S rDNA sequences is consistent with earlier phylogenies and the position of the Hirudinellidae Dollfus, 1932 is well-supported as a derived group most closely related to the Syncoeliidae Looss, 1899. Introduction The Hirudinellidae Dollfus, 1932 is a small cosmo- politan family of robust hemiuroid digeneans that inhabit the stomach of pelagic marine fishes. The life history of members of the family is entirely unknown. The family is represented by approximately 50 nominal species, most in the genus Hirudinella de Blainville, 1828. However, the taxonomy of the family has a confusing history (summarised in Nigrelli & Stunkard, 1947; Gibson, 1976; Gibson & Bray, 1977), and remains unresolved because the morphological features traditionally used to separate species in the genus are few in number and are either unreliable or ineffective at the species level (Gibson & Bray, 1977). In the most recent classification of the family, Gibson (2002), following Gibson (1976), and Gibson & Bray (1977, 1979), assigned all nominal species to belong in three monotypic genera. The oldest of these, Hirudi- nella, is represented by Hirudinella ventricosa (Pallas, 1774) Baird, 1853. The species of Hirudinella are united by having a vitellarium consisting of two lateral fields with their anterior extent at the testicular level and their posterior extent near the middle of the D. M. Calhoun (&) Á S. S. Curran Á E. E. Pulis Á J. S. Franks Department of Coastal Sciences, The University of Southern Mississippi, 703 East Beach Drive, Ocean Springs, MS 39564, USA e-mail: dana.calhoun@colorado.edu J. M. Provaznik Mississippi Laboratories, National Marine Fisheries Services (NOAA), Southeast Fisheries Science Center (SEFSC), 3209 Frederick Street, Pascagoula, MS 39567, USA 123 Syst Parasitol (2013) 86:197–208 DOI 10.1007/s11230-013-9439-2