Diplomonorchis fallax n. sp. (Digenea: Monorchiidae) from the northern Gulf of Mexico with evaluation of sympatric congeners

Syst Parasitol (2025) 102:4 https://doi.org/10.1007/s11230-024-10196-7 Diplomonorchis fallax n. sp. (Digenea: Monorchiidae) from the northern Gulf of Mexico with evaluation of sympatric congeners Stephen S. Curran · Peter D. Olson Stephen A. Bullard · Received: 15 August 2024 / Accepted: 11 October 2024 © The Author(s) 2024 Abstract Diplomonorchis micropogoni Nahhas & Cable, 1964 was considered a junior subjective synonym of Diplomonorchis leiostomi Hopkins, 1941 in 1969. Diplomonorchis leiostomi has since been widely reported from the coastal Western Atlantic between Delaware Bay and southern Brazil. Until now, taxonomically verifiable DNA sequence data for D. leiostomi has been available from an individual worm collected from the northern Gulf of Mexico. We generated a partial sequence of the 28S rRNA gene from D. leiostomi from the spot croaker, Leiostomus xanthurus Lacepède (type-host) from Beaufort, North Carolina, USA (type-locality) that differed at 31 of 1,246 bases from the available 28S sequence. This prompted a reevaluation of Diplomonorchis spp. identities from the northern Gulf of Mexico. We found D. leiostomi and D. micropogoni distinguishable by testes shape and size, and to a lesser degree by relative caecal length. Museum specimens of D. leiostomi, identified from the Gulf of Mexico represent a species complex containing D. leiostomi, D. cf. S. S. Curran (*) · S. A. Bullard Aquatic Parasitology Laboratory and Southeastern Cooperative Fish Parasite and Disease Laboratory, School of Fisheries, Aquaculture, and Aquatic Sciences, College of Agriculture, Auburn University, 559 Devall Drive, Auburn, AL 36832, USA e-mail: P. D. Olson Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK micropogoni and, a new species of Diplomonorchis. The sequences previously identified as D. leiostomi in GenBank (AY222137 & AY222252) are herein identified as D. cf. micropogoni. The new species is described from newly collected material herein. Phylogenetic analysis of 28S rRNA sequences from the species complex plus 46 species from the Monorchioidea Odhner, 1911 indicated all three Diplomonorchis spp. are closely related and form a clade with some species of Lasiotocus Looss, 1907. With the addition of the new species, and acceptance of D. micropogoni, there are currently 14 valid species in Diplomonorchis. Introduction Diplomonorchis Hopkins, 1941 was erected for monorchiid digeneans having two well-separated opposing testes situated entirely in the hindbody, and irregularly shaped vitelline follicles distributed in paired groups in the gonadal region of the hindbody. Hopkins (1941) designated Diplomonorchis leiostomi Hopkins, 1941 as type-species, which he described from the spot croaker, Leiostomus xanthurus Lacepède (type-host) and the pigfish, Orthopristis chrysoptera Linnaeus, from Atlantic coastal waters at Beaufort, North Carolina, USA. Subsequently, D. leiostomi has been reported to infect a variety of coastal fishes in the western Atlantic Ocean (see Table 1) ranging from Delaware Bay (see Thoney, 1993) to Vol.: (0123456789) 4 Page 2 of 27 Syst Parasitol (2025) 102:4 Table 1  Diplomonorchis spp. with their reported definitive hosts, distributions, and associated records. Species Type host D. alexanderi (Arai, 1963) Kumar, 1997 D. bivitellosus (Manter, 1940) Hopkins, 1941 Paralabrax clathratus Eastern Pacific Ocean, (Girard) Mexico Symphurus atramentatus Symphurus plagiusa (L.) Eastern Pacific Ocean, Jordan & Bollman Galapagos Islands Beaufort, North Carolina Unidentified Syacium sp. Gulf of Mexico D. caballeroi (Zhukov, 1983) Gibson, 2013 Syacium papillosum (L.) D. catarinensis Amato, 1982 D. cumingae (Martin, 1938) Amato, 1982 D. floridensis Nahhas & Powell, 1965 Micropogonias furnieri (Desmartest) Unidentified “flounders and eels” S. plagiusa D. hopkinsi Nahhas & Cable, 1964 D. kureh Machida, 2005 M. furnieri D. leiostomi Hopkins, 1941 Vol:. (1234567890) Other host(s) Diagramma pictum (Thunberg) Leiostomus xanthurus Lecepède Geographic range Record(s) Arai, 1963 Manter, 1940 Pearse, 1949 Zhukov, 1983 Gulf of Mexico Chaetodipterus faber (Brousssonet) Unidentified Symphurus sp. Vidal-Martínez et al., 2019 Western Atlantic Ocean, Amato, 1982 Brazil Woods Hole, MassaMartin, 1940 chusetts Gulf of Mexico, Florida Nahhas & Powell, 1965 Western Atlantic Ocean, Wallet & Kohn, 1987 Brazil Caribbean Sea, Jamaica Nahhas & Cable, 1964 Western Pacific Ocean, Japan Diagramma labiosum Western Pacific Ocean, MacLeay Queensland, Australia Orthopristis chrysoptera Western Atlantic Ocean, (L.) Beaufort, North Carolina Pogonias cromis (L.) Gulf of Mexico, Louisiana Gulf of Mexico, Florida Bairdiella chrysura (Lecepède), Lagodon rhomboides (L.) Gulf of Mexico, Florida O. chrysoptera, L. rhomboides Micropogonias undulatus (L.), Monacathus hispidus (L.), L. xanthurus Trinectes maculatus Gulf of Mexico, Loui(Bloch & Schneider) siana Archosargus rhomboida- Biscayne Bay, Florida lis (L.), L. rhomboides, O. chrysoptera Haemulon Sciurus Western Atlantic Ocean, (Shaw) Brazil Boridia grossidens Western Atlantic Ocean, Cuvier Brazil Haemulon steindachneri Western Atlantic Ocean, Brazil (Jordan & Gilbert), Orthopristis rubra Cuvier M. furnieri Western Atlantic Ocean, Brazil Machida, 2005 Searle et al., 2014 Hopkins, 1941 Sparks, 1958* Sogandares-Bernal & Hutton, 1959* Nahhas & Powell, 1965* Corkum, 1966* Overstreet, 1969* Kohn et al., 1982 Fernandes et al., 1985 Luque et al., 1996 Alves & Luque, 1999; Alves & Luque, 2001 Syst Parasitol Page 3 of 27 (2025) 102:4 4 Table 1  (continued) Species Type host D. magnacetabulum (Thomas, 1959) Overstreet, 1969 D. micropogoni Nahhas & Cable, 1964 Cynoglossus senegalensis (Kaup) D. myrophitis Nahhas & Cable, 1964 D. sphaerovarium Nahhas & Cable, 1964 M. furnieri Myrophis punctatus Lütken Sphoeroides testudineus (L.) Other host(s) A. rhomboidalis L. xanthurus L. rhomboides, L. xanthurus, M. undulatus Stellifer lanceolatus (Holbrook) Ophichthus gomesii (Castelnau) O. gomesii Geographic range Record(s) Eastern Atlantic Ocean, Ghana Thomas, 1959 Caribbean Sea, Jamaica Northern Gulf of Mexico Northern Gulf of Mexico Western Atlantic Ocean, Sapelo Island, Georgia Caribbean Sea, Jamaica Nahhas & Cable, 1964 Olson et al., (2003) Present study Caribbean Sea, Jamaica Nahhas & Cable, 1964 Biscayne Bay, Florida Overstreet, 1969 Present study Nahhas & Cable, 1964 Western Atlantic Ocean, Fernandes et al., 2002 Brazil *We consider these reports to represent in full or in part D. cf. micropogoni. coastal Brazil (see Kohn et al., 2007). Hopkins (1941) also created a new combination for a second species, Diplomonorchis bivitellosus (Manter, 1940) Hopkins, 1941, which Manter (1940) had originally described from the halfspotted tonguefish, Symphurus atramentatus Jordan & Bollman from the Pacific Ocean near the Galápagos Islands. These were the only two accepted species in the gen (...truncated)