Bathynomus jamesi Kou, Chen and Li 2017
Creators: name: Huang, Ming-Chih
name: Kawai, Tadashi
name: Bruce, Niel L.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Cirolanidae
Bathynomus
Bathynomus jamesi

description: Bathynomus jamesi Kou, Chen and Li, 2017
Bathynomus giganteus – Soong 1992: 293, figs 1, 2 [not Bathynomus giganteus Milne Edwards, 1879].
Bathynomus kensleyi – Lowry and Dempsey 2006: 184 [South China Sea and Philippine specimens only].
Bathynomus kenleyi – Truong 2015: 81, fig. 2 [lapsus].
Bathynomus jamesi Kou, Chen and Li, in Kou et al. 2017: 285, figs 2–7.
Material examined
Four ovigerous females, Pratas Island voucher numbers TMCD003326, 3329, 3331 and 3332, TL 277–318 mm (avg. 300.5 mm), CL 115–150 mm (avg. 132.3 mm), wet weight 495–1100 g (avg. 823.8 g). Six males (TMCD003327, 003328, 003330, 003333, 003334 and EA0238), TL 309–376 mm (avg. 338.3 mm), CL 150–197 mm (avg. 170.3 mm), wet weight 1125–2000 g (avg. 1489.2 g) (Table 1). Males are slightly larger than females. Six specimens (TMCD003326–3330 and EA0238) were collected by bottom trawl in the northern South China Sea between North Vereker Bank (21.061°N, 116.109°E) and Pratas Island (20.717°N, 116.700°E) by the crew of the Keelung-based fishing vessel Jin Ruiyi 37 on 17 June 2019 (Figure 1), and four specimens (TMCD003331–3334) were collected by bottom trawl about 300 km south-west of Pratas Island (19.084°N, 115.250° E) by the crew of the Keelung-based fishing vessel Jing yang on 12 May 2020. The water depth was about 420– 550 m.
Also examined. Photographs of Bathynomus kensleyi holotype (NTM Cr003425) (Figure 2). Marion Plateau, Coral Sea, QLD, Australia (22.917°S, 154.350°E, depth, 590–606 m, Stn: 0685–08, coll: N.L. Bruce, 17 November 1985, det: J. Lowry 2004) (Photo provided by Gavin Dally, Senior Collections Manager Natural Sciences, Northern Territory Museum), Australia). Imm, 129 mm, off Lihou Reef, Coral Sea, 16.917°S, 155.567°E, 6 October 1985, 880 m, coll. RV Soela (QM W28011). Photographed material identified as Bathynomus kensleyi by Lowry and Dempsey (2006): from Sulu Sea (AM P42711, P42712), south of Hong Kong [Soong (1992) material, NMMB-CD 005878, Taiwan], and material from off Lubang Island, near Manila, Philippines, MNHN IS.2290, IS.2298).
Description of a female (TMCD003332)
Body 2.4 times as long as wide, ovate in shape, coarsely punctate, without sculpture (Figure 3 (a)); 277 mm in TL. Head ridge above eyes discontinuous (Figure 3 (b)). Clypeal region distal margin slightly concave, apex narrowly rounded (Figure 3 (b,c)).
Antennula peduncle 4-articulate (Figure 5 (g)) with 4 articles with exopod at end of peduncular article 4 (Figure 5 (h)); flagellum longer than peduncle. Antenna peduncle article 4 very short (Figure 5 (i)), article 4 about 2.5 times longer than article 3, articles 1–2 bearing neither exopod nor seta (Figure 5 (i)), composed of approximately 50 articles; flagellum longer than peduncle, extending to within pereonite 2 (Figures 3 (d) and 4(a)), composed of approximately 60 articles (near-terminal segmentation unclear).
Palp not reaching to incisor margin (Figure 7 (d)). Maxilla with long setae (Figure 7 (c)); lateral lobe with 9 keratinised spines on exopod, 4 robust spines on endopod (Figure 7 (e)). Maxillipedal endite with 5 equally spaced, robust, spiniform setae (Figure 7 (b)).
Pereopod 1 (Figure 5 (a)) ischium bearing 3 posteroproximal RS and 3 RS on posterodistal margin; merus with 3 RS on an anterodistal angle, proximal row of 3 RS on posterolateral margin, and distal row of 3 RS; propodus twice as long as wide, with 4 RS on posterior margin. Pereopod 2 (Figure 5 (b)) ischium with 3 RS each on posterior and posterodistal margins; merus with 5 short simple setae on an anterodistal angle, 3 RS in a proximal row on posteromedial margin, and distal row of 3 RS; propodus with 4 RS on posterior margin. Pereopod 7 basis 2.5 times as long as greatest width, superior margin convex, inferior margin with 5 palmate setae; ischium 0.7 times as long as basis, inferior margin with 14 RS (4 clusters of 1 + 3 + 6 + 4), superior distal angle with 12 RS, inferior distal angle with 6 RS; merus 0.5 as long as ischium, 2.1 times as long as wide, inferior margin with 6 RS, superior distal angle with 9 RS, inferior distal angle with 8 RS; carpus 0.6 as long as ischium, 1.6 times as long as wide, inferior margin with 5 RS (as 1 + 2), superior distal angle with 13 RS, inferior distal angle with 9 RS; propodus 0.7 as long as ischium, 2.4 times as long as wide, inferior margin with 6 clusters of RS (as 3 clusters of 2), superior distal angle with 4 slender setae, inferior distal angle with 1 RS; dactylus 0.5 as long as propodus.
Oostegites arise from proximal parts of pereopods 1–6 (Figure 5 (f)). Coxa of pereopod 7 distally broadened and slightly curved posteriorly (Figures 4 (a,b)).
Pleon comprising approximately 20% of body length (Figures 3 (a) and 4(a)). Posterolateral angles of pleonites 3–4 reaching to almost the same level posteriorly (Figure 4 (a,b)). Apex of appendix masculina simple and flat (Figure 6 (g)). Penial processes close-set, 0.86 times as long as basal width, distally bluntly rounded (Figure 6 (f)).
Pleotelson (Figure 4 (b,c)) 0.6 times as long as greatest width, smooth except for minute pores, with inconspicuous longitudinal carina on dorsal surface; posterior margin with 11 long, prominent, upwardly curved spines and pair of small posterolateral spines, without setae between spines, central spine simple.
Uropods (Figure 4 (c)) not extending beyond caudal margin of pleotelson. Peduncle with 2 RS on caudolateral margin (Figure 4 (e)). Exopods and endopods both with continuous marginal setal fringes and smooth lateral and distal margins (Figure 4 (d)). Lateral margin of exopod convex with 9 RS, setal fringe continuous 75% (Figure 4 (d)), medial margin straight, distomesial corner rounded, and distal margin convex with 4 RS, distolateral corner slightly produced, subacute. Endopod with subacute distolateral angle, straight lateral margin with 3 RS, straight medial margin, rounded distomesial corner, and straight distal margin with 10 RS, distolateral corner produced, subacute.
Colour of dorsal surfaces dark yellowish-grey; pleotelson light grey; ventral sides of pereopods, pleotelson, and uropods also light grey, but pleopods dark rose (Figure 8 (b)).
Habitat
Continental slope, bathyal to the upper abyss (300–2500 m) (Lowry and Dempsey 2006), Distribution
South China Sea off Hainan Island, south-east of Hong Kong, off Taiwan and off western Luzon Island, Philippines; continental slope at depths between 300 and 925 metres (Lowry and Dempsey 2006).
Variation. Specimens TMCD003326–3334, and EA0238: variation appears in body length/width ratio (1.80–2.55), flagellum length (extending to within pereonite 2 and/ or 3), pleotelsonic length/width ratio (1.51–2.71) and number of pleotelsonic spines (11 or 13). The smallest body length/width ratio is that of TMCD003327 (1.80), and TMCD003331 has the largest (2.55). Length of most flagella length extending to within pereonite 2 but TMCD003328 and TMCD003333 can extend to within pereonite 3. The pleotelsonic length/width ratio is also very different, with TMCD003330 being the smallest at 1.51, and TMCD003327 being the largest at 2.71. For most specimens the number of pleotelsonic spines is 13, but TMCD003329 and TMCD003330 have 11 (Table 1).
Molecular biology. Amplified PCR products of 497 bp from 16S rRNA and 657 bp from COI, respectively, were obtained for the 16S rRNA and COI nucleotide sequences of one (TMCD003329) and nine (TMCD003326–003333) of our specimens B. jamesi (Table 1), respectively. The results of COI alignment showed that samples collected from Pratas Island are the same species as B. jamesi (Figures 10 and 11). The sequence data have been uploaded to the DNA Data Bank of Japan (DDBJ)/ European Molecular Biology Laboratory (EMBL)/ GenBank (Acc. Nos. MW575424, MW575449, MW575454, MW575455, MW580729, and MW580730 for COI, and MZ029589 for 16S rRNA). The variation in the 657-bp COI gene sequences cloned from individual Bathynomus involved 7 positions, with the less prevalent base-pairing usually occurring in just 1 or 2 specimens: c. 90T>C (MW577651), c. 255T>C (MW575454), c. 302T>C (MW575424), c. 498 A>G (MW575424), c. 558G>T (MW575454), and c. 573C>T (MW575449). The greate st number and variety of mutations were found at position 348: c. 348 A>T (MW575455), (MW580729), (MW580730), and c. 348 A>C (MW577651), (MW577652) (Figure 11).
After COI and 16S rRNA sequencing, and comparison with the NCBI databank, the results confirmed that the 10 specimens were all B. jamesi (Figure 11). The immature and juvenile specimens do not necessarily exhibit all the species characteristics found in fully adult specimens; in particular, the form of the pleotelson spines may be substantially different. So, new species should never be based on sub-adults (of any stage) where related species are very similar.
Remarks
Bathynomus jamesi was described from Hainan Island in the northern South China Sea (Kou et al. 2017). The diagnosis was ‘pleotelson with 11 or 13 short, straight spines; central spine not bifid. Uropod with endopod and exopod distolateral corner slightly produced. Clypeus lateral margins concave, narrowly rounded apically. Antennal flagellum extending to within pereonite 3’. Kou et al. (2017) did not describe any upward curvature of the pleotelsonic spines in their specimens from Hainan Island, something that is obvious in all 10 of our specimens. Another difference is the shorter antennal flagellum in our material, extending to pereonite 2 (a few to pereonite 3, see Table 1) but in the holotype and the original description by Kou et al. (2017) it is described as extending to pereonite 3.
Bathynomus kensleyi Lowry and Dempsey, 2006 was described from off the Great Barrier Reef, Queensland, with additional material from the Philippines and from ‘south of Hong Kong’. An examination of good-quality photos of the holotype of B. kensleyi (Figure 2) shows several distinct points of difference between B. jamesi and B. kensleyi: in B. jamesi the clypeus has a weakly produced median point, with lateral margins that converge towards the anterior, and the anterior margins are weakly concave (in B. kensleyi the median point is strongly produced, the lateral margins are parallel; the anterior margins strongly concave); in B. jamesi pleonite 3 laterally extends posteriorly to the posterior of pleonite 4 and does not exceed pleonites 4 and 5 (in B. kensleyi pleonite 3 laterally extends past both pleonites 4 and 5 and reaches the anterior of the pleotelson, and pleonite 4 also extends to just posterior of pleonite 5); other differences include the uropodal exopod being proportionally shorter than in B. kensleyi and the posterior margin of the pleotelson being slightly narrower (0.9 times as wide as anterior width) than in in B. kensleyi (1.0 times as wide as anterior width). The characters of the clypeus and pleon allow for identification of these two similar species. Lowry and Dempsey’s (2006) synonymy included the record of Soong (1992) from the South China Sea. The figures given by Soong (1992) agree with B. jamesi with regard to the morphology of the pleon, clypeus and pleotelson, confirming that B. kensleyi does not occur in the South China Sea. The Bathynomus specimens identified as B. kensleyi in Lowry and Dempsey (2006) from the northern Philippines are in fact B. jamesi, but those from the Sulu Sea are neither B. jamesi nor B. kensleyi, and appear to be an undescribed species (see ‘Discussion’).
The 10 B. jamesi collected from Pratas Island share the common feature of a huge body size (277 to 376 mm, all specimens), with 11 upwardly curved pleotelsonic spines (Figures 3 (a) and 4(a,c)). According to Lowry and Dempsey’s (2006) description, only two Bathynomus species, B. kensleyi and B. lowryi, have these characteristic upwardly curved pleotelsonic spines. The present specimens display all the diagnostic characteristics of B. jamesi from Kou et al. (2017), but the pleotelsonic spines, not described in the diagnosis, are different. In Kou et al.’s (2017) specimens the pleotelson spines project straight (or perhaps just slightly angled up in lateral view), in line with the pleotelson (Kou et al. 2017), Figure 1 (b), whereas in the present material they are upturned. Given that the molecular data shows that all these specimens are the same species, and in the absence of other morphological difference, we conclude that the development of pleotelson spines is an expression of age and maturity; the Kou et al. (2017) specimens are small juveniles and one small immature specimen, so adult characteristics were not assessed. Bathynomus jamesi is the third species of Bathynomus to show strongly produced and dorsally directed pleotelson spines in the mature individuals of both sexes.
The colouration of B. lowryi Bruce and Bussarawit, 2004 from Thailand is similar to that of the present specimens of B. jamesi (Figure 8 (a)), except that the pleopods of B. lowryi are grey and dark orange, not dark rose (Bruce and Bussarawit 2004).
The presence of oostegites on the pereopods of the present females (TMCD003332) indicates that B. jamesi reaches maturity before attaining a body length of 277 mm.
description: Published as part of Huang, Ming-Chih, Kawai, Tadashi & Bruce, Niel L., 2022, A new species of Bathynomus Milne-Edwards, 1879 (Isopoda: Cirolanidae) from the southern Gulf of Mexico with a redescription of Bathynomus jamesi Kou, Chen and Li, 2017 from off Pratas Island, Taiwan, pp. 885-921 in Journal of Natural History 56 (13 - 16) on pages 890-902, DOI: 10.1080/00222933.2022.2086835, http://zenodo.org/record/7012152