Bathynomus vaderi Ng, Sidabalok & Nguyen, 2025, sp. nov.
Creators: name: Ng, Peter K. L.
name: Sidabalok, Conni M.
name: Nguyen, Thanh Son
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Cirolanidae
Bathynomus
Bathynomus vaderi

description: Bathynomus vaderi sp. nov.
Figs 4, 5, 6, 7, 8, 9 A – D, 10 A
Material examined.
Holotype, Vietnam, ♂; 266 mm; offshore of Quy Nhơn City, Bình Đ ịnh Province, south-central Vietnam, ca. 50 nautical miles from shore, from deep-water (depth not known); purchased by Tran Anh Duc from Eo Gió, Nhơn Lý commune; 27 March 2022; ZRC 2022.0621. Paratypes: 1 ♂; 270 mm; same data as holotype; ZRC 2024.0176 • 1 ♂; 258 mm; same data as holotype; ZVNU 110001 • 1 ♂; 257 mm; same data as holotype; ZVNU 110002 • 2 ♂; 325 mm, 295 mm; collected by trawlers operating off Qu ảng Ngãi, Bình Đ ịnh, Khánh Hòa and / or Phú Yên Provinces, central Vietnam; purchased by Nguyen Thanh Son from seafood restaurant in Đà N ẵng City, Vietnam; September 2024; ZRC 2024.0180.
Type locality.
Offshore of Quy Nhơn, ca 50 nautical miles from shore, south-central Vietnam, west of the Spratly Islands.
Diagnosis.
Clypeal region with lateral margin parallel, distal margin concave, apex narrowly acute, transversely rectangular (Figs 4 C, 5 C, 6 C, 9 A). Coxa of pereopod 7 narrows distally, curved posteriorly (Figs 5 D, 6 D, E, 9 B). Distinct row of setae present between pleotelson spines; 11 upwardly curved pleotelson spines; pleotelson 0.6 as long as wide (Figs 5 A, 9 D); pleotelson vaulted laterally (Figs 6 E, 9 C). Appendix masculina slightly shorter than or reaching to end of endopod of pleopod 2 (Fig. 10 A).
Description of male holotype.
Body (Figs 4 A, B, 5 A, 6 A) 266 mm long, 135 mm wide at pereonite 5, length 1.9 times width, ovate in shape, coarsely punctate, without sculpture (Figs 4 A, 5 A, 6 A). Head ridge above eyes discontinuous (Figs 4 C, 5 B, 6 B). Clypeal region transversely rectangular, lateral margins parallel, distal margin slightly concave, apex narrowly subacute (Figs 4 C, 5 C, 6 B, C, 9 A).
Antennula (Fig. 6 B); flagellum 1.2 longer than peduncle. Antenna peduncle article 4 - articulate (Fig. 6 B), article 4 about 1.4 times longer than article 3 (Fig. 6 B), flagellum extending to within pereonite 2 (Fig. 6 A, B).
Mandible (Fig. 7 D) palp not reaching incisor, with setal fringe on lateral margin of distal half of article 2 and along article 3. Maxillula (Fig. 7 E) mesial lobe with 4 robust setae, lateral lobe with 9 keratinised robust setae. Maxilla (Fig. 7 C) lateral lobe with 9 keratinised robust setae, middle lobe with 7 keratinised robust setae, mesial lobe with fringe of long plumose setae. Maxilliped palp (Fig. 7 A) typical of genus; maxilliped endite with 4 coupling hooks (Fig. 7 B).
Pereopod 1 (Fig. 8 A) ischium with 1 posteroproximal robust seta and 3 robust setae on posterodistal margin; merus with 6 robust setae on anterodistal angle, posterolateral margin with 4 robust setae in proximal row on and 3 robust setae in distal row; propodus 2.3 as long as wide, with 4 robust setae on posterior margin. Pereopod 2 (Fig. 8 B) ischium with 3 robust setae on posterior margin and 4 robust setae on posterodistal margin; merus with 9 robust setae on anterodistal angle, posteromedial margin with 3 robust setae in proximal row and 3 robust setae in distal row; propodus with 4 robust setae on posterior margin. Pereopod 7 (Fig. 8 C) basis 3.5 times as long as greatest width, inferior margin convex; ischium 0.5 times as long as basis, inferior margin with 1 robust seta, superior distal angle with 6 robust setae, inferior distal angle with 6 robust setae; merus 0.6 as long as ischium, as long as wide, inferior margin with 1 robust seta, superior distal angle with 11 robust setae, inferior distal angle with 13 robust setae; carpus as long as ischium, 2 times as long as wide, inferior margin with 3 robust setae (as 1 + 2), superior distal angle with 13 robust setae, inferior distal angle with 10 robust setae; propodus 0.9 as long as ischium, 3.8 times as long as wide, inferior margin with 2 clusters of robust setae (as 2 clusters of 2), superior distal angle with 8 robust setae, inferior distal angle with 1 robust seta; dactylus 0.5 as long as propodus. Coxa of pereopod 7 distally narrowed, gently curved posteriorly (Figs 5 D, 6 E, 9 B).
Pleonite 3 (Fig. 6 E) not extending beyond pleonite 5. Pleonite 4 (Fig. 6 E) reaching to end pleonite 5. Penial process flat lobes (Fig. 4 B). Appendix masculina with parallel margins, not extending beyond endopod, distally narrowly rounded (appendix masculina absent on holotype male) (Fig. 10 A).
Pleotelson (Figs 5 A, 6 F, 9 C, D) 0.6 time as long as greatest width, smooth (minute pores), with inconspicuous longitudinal carina on dorsal surface; dorsal surface distinctly convex (Figs 5 D, 6 E, 9 C, D); posterior margin with 11 long, prominent, upwardly curved spines and pair of small posterolateral spines, with setae between spines, central spine simple.
Uropods (Figs 4 A, 6 F, 8 D, E) not extending beyond pleotelson. Peduncle with 3 short robust setae on caudolateral margin (Fig. 8 D); exopod and endopod with smooth lateral and distal margins; exopod lateral margin convex with 12 left and 11 right robust setae along margin, setal fringe continuous length (83.3 %), medial margin straight, distomedial corner rounded, distal margin convex with 5 left and 7 right robust setae, distolateral corner produced, acute; endopod lateral margin convex, distally straight, with 5 left and 6 right robust setae; medial margin posteriorly convex; distomedial corner rounded; distal margin straight with 12 left and 13 right robust setae; distolateral corner produced, acute.
Female. Not known.
Variation.
Paratype robust setae counts as follows exopodal lateral margin with 9–13 robust setae, distal margin with 4–6, endopodal lateral margin with 1, 4 and 5 and distal margin with 10–14; pleotelson with 11 upwardly curved spines and one paratype with addition 2 small posterolateral spines. The holotype lacks the appendix masculina, but it is present in the other type specimens (Fig. 10 A). As discussed by Barradas-Ortiz et al. (2003), these structures may be lost and regrow at different moults throughout the life of the animal.
Etymology.
The species named after the most famous Sith Lord in the Star Wars movie series, Darth Vader, whose helmet resembles the head of the new Bathynomus species.
Distribution.
Known only from Vietnam. We are unable to determine the exact location where B. vaderi was trawled, as the dealers and fishermen would only say they were obtained from deep waters off Vietnam near the Spratly Islands.
Remarks.
Bathynomus vaderi sp. nov. can be distinguished by the parallel margin of clypeal region, rectangular shape of clypeal region, the posteriorly curved coxa of pereopod 7, upwardly curved spines of the pleotelson, setae between pleotelson spines, and the laterally vaulted pleotelson. Bathynomus vaderi is the fourth species with upwardly curved pleotelson spines.
Bathynomus vaderi is very similar to the congeners with upwardly curved pleotelson spines, i. e., B. jamesi, B. kensleyi, and B. lowryi Bruce & Bussarawit, 2004. Other similarities with B. jamesi are in the length of antennae, which reaches pereonite 2, the number of pleotelson spines, pleonite 4 extending beyond pleonite 5, uropod endopod reaching the end of the pleotelson and beginning of central pleotelson spine, exopod and endopod distolateral angle is produced and subacute. Bathynomus vaderi, however, differs from B. jamesi in the following character states: the lateral margins of the clypeal region are parallel (Figs 4 C, 5 C, 9 A) (vs gently converging distally in B. jamesi; Fig. 9 E); the apex of the clypeal region is acute (Figs 4 C, 5 C, 9 A) (vs obtusely rounded in B. jamesi; Fig. 9 E); the clypeus is transversely rectangular in shape (Figs 4 C, 5 C, 9 A) (vs square or subquadrate; Fig. 9 E); the distolateral corners of the uropod endopod and exopod are acute (Fig. 8 D, E) (vs subacute in B. jamesi; Huang et al. 2022: fig. 4 d, e); the P 7 coxa has the lateral margins more sinuous, with the posterior margin distinctly concave in form towards the tip (Figs 6 E, 9 B) (vs margins less sinuous with the posterior margin only slightly concave towards the tip in B. jamesi; Fig. 9 F); the dorsal surface of the pleotelson is distinctly raised, being gently convex in lateral view (Figs 5 D, 6 D, 9 D) (vs almost flat or only slightly convex in lateral view in B. jamesi; Fig. 9 H); there are numerous short setae present between the pleotelson spines (Fig. 9 C) (vs absent or only with scattered setae in B. jamesi; Figs 3, 9 G); and the appendix masculina is shorter, just reaching to edge of endopod of pleopod 2 (Fig. 10 A) (vs distinctly longer, reaching well beyond edge of endopod of pleopod 2 in B. jamesi; Fig. 10 B – D). Bathynomus vaderi and B. jamesi are sympatric congeners in the South China Sea, a pattern of co-occurrence which has been discovered before in B. giganteus, B. yucatanensis, and B. maxeyorum from Gulf of Mexico (Huang et al. 2022).
The denser setation between the pleotelson spines is diagnostic for B. vaderi but may not be a reliable character once a larger series of specimens is collected. We note that, in B. jamesi, most of the specimens do not have setae or only a few scattered ones between the pleotelson spines. In a few specimens (from the recent material from Vietnam), however, the setae are slightly denser, although not to the same degree observed in B. vaderi.
Bathynomus vaderi is similar to B. kensleyi in the clypeal region characters, i. e., parallel margin, concave distal margin and rectangular shape; and uropod endopod characters, i. e. straight distal margin with produced acute distolateral corner. Bathynomus vaderi differs from B. kensleyi in having the clypeal region with a pointed apex (Figs 4 C, 5 C, 6 C, 9 A) (vs rounded in B. kensleyi; Lowry and Dempsey 2006: fig. 18 E; Huang et al. 2022: fig. 2 b), 11 spines on the pleotelson (Figs 4 A, 5 A, 6 F, 9 A) (vs 9 in B. kensleyi; Lowry and Dempsey 2006: fig. 18 A, F; Huang et al. 2022: fig. 2), the pleotelson broader than long (Figs 5 A, 6 F, 9 A) (vs longer than broad in B. kensleyi; Lowry and Dempsey 2006: fig. 18 A, F; Huang et al. 2022: fig. 2), the uropod exopod distolateral corner produced and acute (Fig. 8 D, E) (vs not produced in B. kensleyi; Lowry and Dempsey 2006: fig. 19 D, E), and the posterior end of pleonites 3 and 4 not reaching beyond the posterior end of pleonite 5 (Figs 5 D, 6 E) (vs pleonite 3 exceeds pleonites 4 and 5; pleonite 4 reaches the end of pleonite 5 in B. kensleyi; Lowry and Dempsey 2006: fig. 18 B, C; Huang et al. 2022: fig. 2 a).
Other than sharing the upwardly curved pleotelson spines, there are other similarities between B. vaderi and B. lowryi: the antenna flagellum extends within pereonite 2, the clypeus is rectangular, and the pleotelson is broader than long. Both species, however, differ in having the apex of the clypeal region pointed (Figs 4 C, 5 C, 6 C, 9 A) (vs truncated in B. lowryi; Bruce and Bussarawit 2004: fig. 1 C), 11 spines on the pleotelson (Figs 4 A, 5 A, 6 F, 9 C) (vs seven in B. lowryi; Bruce and Bussarawit 2004: figs 1 A, 4 A, 5), setae between the pleotelson spines (Figs 5 A, 9 C) (vs absent in B. lowryi; Bruce and Bussarawit 2004: figs 1 A, 5), an inconspicuous longitudinal carina on the dorsal surface of the pleotelson (Figs 5 A, 9 C) (vs conspicuous in B. lowryi; Bruce and Bussarawit 2004: figs 1 A, 4 A, 5), a continuous setal fringe on the exopod of the uropod, which covers 83 % of the margin (Fig. 8 D, E) (vs fringe of medium length, covering 67 % of margin in B. lowryi; Bruce and Bussarawit 2004: fig. 4 B, C), and a convex lateral margin of the uropod exopod (Fig. 8 D, E) (vs strongly convex and expanded in B. lowryi; Bruce and Bussarawit 2004: fig. 4 B, C).
Huang et al. (2022) excluded the material from Sulu Sea previously considered to be B. kensleyi by Lowry and Dempsey (2006) and treated it as an undescribed species based on the states of the pereon, pleonite, maxilliped, pleotelson spines, and other characters. Based on the above characters reported by Huang et al. (2022) (species was not figured), the Sulu material is similar to B. vaderi in possessing more slender pleotelson spines and pleonite 4 that does not extend beyond end of pleonite 5. The two taxa, however, are different, as the Sulu Sea individual has a strongly convex uropodal exopod lateral margin (vs convex in B. vaderi, Fig. 8 D, E). Furthermore, Shane Ahyong (pers. comm.) has compared specimens of B. vaderi with the Sulu Sea material, which is in the Australian Museum, and he comments that they are different taxa.
A note on the Bathynomus fishery
In Vietnam, Bathynomus, known locally as b ọ bi ển or “ sea bugs ”, has been fished for food apparently since 2017. Specimens are caught in deep water by trawlers operating in various parts of Bi ển Đông (= East Sea, Vietnamese part of the South China Sea) and brought back to shore alive in ice boxes. The isopods are kept out of water and chilled, and in this state, can survive for many days if well insulated. They are then transported to restaurants for sale. Smaller eating establishments keep the isopods in ice boxes to be cooked when asked, while large restaurants have dedicated tanks with chilled water to keep and display the animals (Fig. 11). One local restaurant owner in Eo Gió in Nhơn Lý commune (Quy Nhơn City, Bình Đ ịnh Province), who was selling these isopods, explained that Bình Đ ịnh, which is a coastal province at south-central Vietnam, is the main area where the isopods are caught, and a number of fishermen target these animals. Once every few days, this restaurant receives the catch from the fishermen, usually about 10 individuals each time. He also knows that they are sent alive to restaurants in Hanoi, where there is a high demand for them (Tran Anh Duc pers. comm. 2022). In Hanoi, Bathynomus once was sold at high prices, but this has decreased over the years. In 2017, the price was up to 2 million Vietnamese Dong (ca USD $ 80) per kilogram, with large individuals reaching 2 kg in weight (Bang 2017). As noted above, large specimens of B. jamesi can reach weights in excess of 2.5 kg. Because of these prices, fishermen started to increase the supply, and by 2023 the price dropped to around 1.5 million Vietnamese Dong per kilogram (An 2023); by early 2024, it was about 1 million Vietnamese Dong (ca USD $ 40) per kilogram for 1–2 kg individuals. In 2017, specimens had to be pre-ordered, and diners had to wait up to a month to collect their Bathynomus specimens in seafood outlets in Hanoi (Bang 2017). Today, some seafood markets in Hanoi, H ồ Chí Minh City, and Đà N ẵng City keep up to 30 individuals in their chilled water tanks for customers to buy. It is also common to see advertisements selling “ sea bugs ” on social network by some seafood stores. Once they are purchased online, the stores will immediately ship the alive animals in icebox to customers. Individuals weighing between 0.6–0.9 kg are the best sellers because the price is more affordable. Large specimens in excess of 2 kg are also sought after as they are less common, and their size makes for an impressive dish. In mid- 2024, prices in some places in Hanoi have dropped and cost only 0.68 million Vietnamese Dong (ca USD $ 27) per kilogram. The prices of these animals, however, do vary quite a bit due to supply and demand, and can cost substantially more in higher end restaurants.
It is noteworthy that four type specimens of B. vaderi were obtained from dealers in Quy Nhơn in south-central Vietnam, where the isopods are fished. In the restaurants in Hanoi where Bathynomus is also sold, we have only seen B. jamesi so far, although we were told the specimens are also from Quy Nhơn. It is possible B. vaderi has a slightly different habitat, depth range, or distribution than B. jamesi, and what is caught depends on where individual boats trawl. In the early 2020 s, Bathynomus was also sold for high prices in Taiwan for food, often cooked with noodles in niche restaurants (Everington 2023), with fishermen collecting them from the Pratas Islands. Fishermen collecting Bathynomus for restaurants in Taiwan in these islands were also the source of the material reported by Huang et al. (2022) (Huang Ming-Chih pers. comm.). During the last year, however, Bathynomus, is no longer popular in Taiwan, and few places sell it now (Chan Tin-Yam pers. comm.). All the supergiant specimens we know of and / or have seen from Pratas and Taiwan belong to only one species, B. jamesi.
description: Published as part of Ng, Peter K. L., Sidabalok, Conni M. & Nguyen, Thanh Son, 2025, A new species of supergiant Bathynomus A. Milne-Edwards, 1879 (Crustacea, Isopoda, Cirolanidae) from Vietnam, with notes on the taxonomy of Bathynomus jamesi Kou, Chen & Li, 2017, pp. 289-310 in ZooKeys 1223 on pages 289-310, DOI: 10.3897/zookeys.1223.139335