Two New Genera and Species of the Parasitic Copepod Family Chondracanthidae Milne Edwards, 1840 (Copepoda: Cyclopoida) from Deep-Sea Fishes Off Suruga Bay, Japan

Acta Parasitologica (2024) 69:874–888 https://doi.org/10.1007/s11686-024-00820-3 ORIGINAL PAPER Two New Genera and Species of the Parasitic Copepod Family Chondracanthidae Milne Edwards, 1840 (Copepoda: Cyclopoida) from Deep‑Sea Fishes Off Suruga Bay, Japan Panakkool Thamban Aneesh1,2 · Susumu Ohtsuka1,3 · Yusuke Kondo1 · Ameri Kottarathil Helna4 Received: 17 November 2023 / Accepted: 24 January 2024 / Published online: 11 March 2024 © The Author(s) 2024 Abstract Purpose The present paper describes two new genera and species of the parasitic copepod family Chondracanthidae Milne Edwards, 1840 based on specimens collected from two species of deep-sea fishes at a depth of 212 m off Suruga Bay, Japan. Avatar nishidai gen. et sp. nov. is described from the host fish Chaunax abei Le Danois, 1978 (Chaunacidae). Kokeshioides surugaensis gen. et sp. nov. is described from the host fish Setarches longimanus (Alcock, 1894) (Setarchidae). Methods Fresh specimens of chondracanthids were collected from the buccal cavity of two species of deep-sea fishes (fish hosts were frozen), Chaunax abei Le Danois, 1978 (Lophiiformes: Chaunacidae) and Setarches longimanus (Alcock, 1894) (Perciformes: Setarchidae), caught at a depth of 212 m in Suruga Bay, Japan (34° 37′48.87″ N, 138° 43′2.958″ E). Both the species are described and illustrated based on ovigerous females. Results The genus Avatar gen. nov. can readily be distinguished from all other chondracanthid genera by the following combination of features: cephalothorax slightly wider than long with anterior pair of large and posterior pair of small lateral lobes, and two pairs of ventro-lateral processes; the very posteriormost part of the first pedigerous somite contributes to the neck; cylindrical trunk with two pairs of blunt proximal fusiform processes; antennule with small knob terminally; antenna bearing distal endopodal segment; labrum protruding ventrally; two pairs of biramous legs each with 2-segmented rami. Kokeshioides gen. nov. has the following combinations of features that distinguish it from other chondracanthid genera: body flattened, without lateral processes; cephalothorax much wider than long, with paired anterolateral and posterolateral lobes, folded ventrally; the very posteriormost part of the first pedigerous somite contributes to the neck; mandible elongate; legs unique, heavily sclerotized, represented by two pairs of acutely pointed processes. Conclusion With the addition of two new genera presently reported, the family Chondracanthidae currently includes 52 valid genera. Among the described genera Avatar gen. nov. seems to be very primitive, while Kokeshioides gen. nov. is highly advanced. The deduced evolutionary history of chondracanthid genera is also discussed. Keywords Avatar nishidai gen. et sp. nov. · Chondracanthids · Copepoda · Fish parasite · Kokeshioides surugaensis gen. et sp. nov 2 * Susumu Ohtsuka Travancore Nature History Society (TNHS), MBRRA , Mathrubhumi Road, Vanchiyoor, Trivandrum, Kerala 695035, India 3 * Ameri Kottarathil Helna Universiti Sultan Zainal Abidin, Gong Badak Campus, 21300 Kuala Terengganu, Terengganu, Malaysia 4 Regional Forensic Science Laboratory, Kannur, Kerala 670002, India * Panakkool Thamban Aneesh 1 Blue Innovation Division, Seto Inland Sea Carbon Neutral Research Center, 5‑8‑1 Minato‑Machi, Takehara, Hiroshima 725‑0024, Japan Vol:.(1234567890) Acta Parasitologica (2024) 69:874–888 875 Introduction Studies on parasitic copepods infecting deep-sea fishes are still rare in comparison with those on shallow-water taxa. Deep-sea parasitic copepods are highly restricted to some genera belonging to the following families: Pennellidae Burmeister, 1835, Chondracanthidae Milne Edwards, 1840, Sphyriidae Wilson, 1919, Hyponeoidae Heegaard, 1962, and Hatschekiidae Kabata, 1979 (see Table 1 in Boxshall) [1]. The Chondracanthidae is one of the most speciose copepod families, that utilize fishes as hosts accommodating nearly 192 species in 50 valid genera [2]. Among them, 27 genera are monotypic and only two genera have more than ten species, Acanthochondria Oakley, 1930 with 54 valid species, and Chondracanthus Delaroche, 1811 with 41 valid species [2–6]. Molecular analyses are absolutely needed to confirm the validity of monotypic genera. The documentation of the parasitic copepod fauna in Japanese waters began with the significant contributions by Yamaguti [7], Yamaguti and Yamasu [8], Wilson [9, 10], Shiino [11, 12] and Izawa [13], followed by Ohtsuka et al. [14, 15], Uyeno and Nagasawa [16] and Nagasawa et al. [17]. The family Chondracanthidae is comparatively well documented in Japanese waters, with 48 valid species in 20 genera (see Nagasawa et al. [17]). In the presently reported study, we describe two new genera and species collected from two species of deep-sea fishes in Suruga Bay, Japan. Chaunacidae) and Setarches longimanus (Alcock, 1894) (Perciformes: Setarchidae), caught at a depth of 212 m in Suruga Bay, Japan (34°37′48.87″ N, 138°43′2.958″ E). Methods for preservation, dissection, mounting, and drawing of appendages were according to the techniques described in Aneesh et al. [18–21]. The specimens were microphotographed using Olympus microscopes (Olympus SZX7 and Olympus Bx50, Olympus Co., Ltd.) and image-capturing software (DP2-SAL, Olympus Co., Ltd). Total body length was measured (without egg sacs) from the anterior margin of the cephalothorax to the distal end of the caudal rami. Drawings were digital-inked using Adobe Illustrator and a WACOM CTL-472/K0-c drawing pad. Morphological terminology follows Huys and Boxshall [22]. The taxonomy and nomenclature of host fishes were adopted from Catalogue of Fishes [23] and FishBase [24]. The type material is deposited in the National Museum of Nature and Science, Tsukuba, Japan. Taxonomy Order Cyclopoida Burmeister, 1834 Family Chondracanthidae Milne Edwards, 1840 Genus Avatar gen. nov. Specimens of chondracanthids were collected from the buccal cavity of two species of deep-sea fishes (fish hosts were frozen), Chaunax abei Le Danois, 1978 (Lophiiformes: Type species: Avatar nishidai gen. et sp. nov. by original designation. Diagnosis based on the adult female (bold = key features). Body small, flattened. Cephalothorax and first pedigerous somite fused forming cephalothorax. Cephalothorax, slightly wider than long with anterior pair of large and posterior pair of small lobes, and two pairs of ventro-lateral processes; latter processes located at level of mouthparts. The very posterior most part of the first Table 1  Character differences between the closely related chondracanthid genera, Avatar gen. nov., Kokeshioides gen. nov., Blias Krøyer, 1863, Diocus Krøyer, 1863, Humphreysia Leigh-Sharpe, 1934, Immanthe Leigh-Sharpe, 1934, and Juanettia Wilson, 1921 collated from original descriptions and, where applicable, redescriptions (see Wilson 1921; Ho 1969, 1994) Materials and Methods Chara (...truncated)