Bathynomus paracelensis, Huang & Kawai, 2025

Bathynomus paracelensis sp. nov.

Restricted synonymy: A. Milne-Edwards, 1879: 21; Bruce, 1986 126: Kensley and Schotte 1989: 129; Soong, 1992: 293, figs. 1, 2, Lowry and Dempsey, 2006: 184, figs. 18, 19; Kou, Chen and Li 2017: 285, figs. 2-7; Huang, Kawai and Bruce, 2022: 890, figs. 3-7.

Type species: B. giganteus A. Milne Edwards, 1879 View in CoL ; by monotype (Bruce 1986).

Materials

Type status: Holotype. Occurrence: occurrenceRemarks: bottom trawl by the crew of Keelung-based fishing vessel Jing yang; recordedBy: Ming-Chih Huang; sex: female; lifeStage: adult; preparations: whole animal; associatedSequences: Gene Bank: PP 715922, PP 719190; occurrenceID: A48C2F53-9A55-5317-81A0-A67C34838E86; Taxon: scientificNameID: urn:lsid:zoobank.org:pub:6D47380F-55E5-47CA-B692-8F6176477FB0 ; scientificName: Bathynomus paracelensis ; kingdom: Animalia; phylum: Arthropoda; class: Malacostraca; order: Isopoda ; family: Cirolanidae ; genus: Bathynomus ; Location: higherGeography: South China Sea; waterBody: South China Sea; islandGroup: Paracel Islands; island: Paracel Island; country: Taiwan; countryCode: Taiwan / TW; county: Taiwan; verbatimDepth: 300-550 m; minimumDepthInMeters: 300; maximumDepthInMeters: 550; verbatimCoordinates: 19.08333 N, 115.25 E; Identification: identifiedBy: Ming-Chih Huang; dateIdentified: 2024-04 - 28; Geological context: earliestEonOrLowestEonothem: Miocene; latestEonOrHighestEonothem: Miocene; Event: samplingProtocol: bottom trawl; year: 2023; month: 1; day: 28; verbatimEventDate: 2023-01 - 28; habitat: Continental slope; Record Level: type: PhysicalObject; modified: 2023-01 - 28; language: en; rightsHolder: National Museum of Marine Biology, Checheng, Taiwan; accessRights: not-for-profit use only; bibliographicCitation: Bathynomus paracelensis ( NMMB-CD 006300 ) for a specimen; institutionCode: National Museum of Marine Biology (NMMB); ownerInstitutionCode: NMMB; basisOfRecord: PreservedSpecimen GoogleMaps

Type status: Paratype. Occurrence: occurrenceRemarks: bottom trawl by the crew of Keelung-based fishing vessel Jing yang; recordedBy: Ming-Chih Huang; sex: female; lifeStage: adult; reproductiveCondition: embryos; associatedSequences: Gene Bank: PP 715921, PP 719187; occurrenceID: E42C574E-7C12-5F96-A847-BA305D429F0F; Taxon: scientificName: Bathynomus paracelensis ; kingdom: Animalia; phylum: Arthropoda; class: Malacostraca; order: Isopoda ; family: Cirolanidae ; genus: Bathynomus ; Location: waterBody: South China sea; islandGroup: Paracel Islands; island: Paracel Island; country: Taiwan; countryCode: Taiwan / TW; county: Taiwan; verbatimDepth: 300-550; minimumDepthInMeters: 300; maximumDepthInMeters: 550; verbatimCoordinates: 19.08333 N, 115.25 E; verbatimLatitude: 19.08333 N; verbatimLongitude: 115.25 E; Identification: identifiedBy: Ming-Chih Huang; dateIdentified: 2024-4 - 28; Geological context: earliestEraOrLowestErathem: miocene; Event: samplingProtocol: bottom trawl; eventDate: 2023-1 - 28; startDayOfYear: 2023; year: 2023; month: 1; day: 28; habitat: continental slope; Record Level: type: PhysicalObject, ovigerous; modified: 2023-01 - 28; language: en; rightsHolder: National Museum of Marine Biology, Checheng, Taiwan; accessRights: not-for-profit use only; bibliographicCitation: Bathynomus paracelensis ( NMMB-CD 006299 ) for a specimen; institutionCode: National Museum of Marine Biology (NMMB); basisOfRecord: PreservedSpecimen GoogleMaps

Type status: Paratype. Occurrence: occurrenceRemarks: bottom trawl by the crew of Keelung-based fishing vessel Jing yang; recordedBy: Ming-Chih Huang; sex: female; lifeStage: adult; preparations: whole animal; associatedSequences: Gene Bank: PP 715923, PP 719189; occurrenceID: 2EC78856-F8BA-5D36-89E4-0A8C300783D4; Taxon: scientificName: Bathynomus paracelensis ; kingdom: Animalia; phylum: Arthropoda; class: Malacostraca; order: Isopoda ; family: Cirolanidae ; genus: Bathynomus ; Location: waterBody: South China Sea; islandGroup: Paracel Islands; island: Paracel Island; countryCode: Taiwan / TW; county: Taiwan; verbatimDepth: 300-550 m; minimumDepthInMeters: 300; maximumDepthInMeters: 550; verbatimCoordinates: 19.08333 N, 115.25 E; verbatimLatitude: 19.08333 N; verbatimLongitude: 115.25 E; Identification: identifiedBy: Ming-Chih Huang; dateIdentified: 2024-4 - 28; Geological context: earliestEraOrLowestErathem: miocene; Event: eventDate: 2023-1 - 28; year: 2023; month: 1; day: 28; habitat: continetal slope; Record Level: type: PhysicalObject; modified: 2023-01 - 28; language: en; rightsHolder: National Museum of Marine Biology, Checheng, Taiwan; accessRights: not-for-profit use only; bibliographicCitation: Bathynomus paracelensis ( NMMB-CD 006301 ) for a specimen; institutionCode: National Museum of Marine Biology (NMMB); basisOfRecord: PreservedSpecimen GoogleMaps

Type status: Paratype. Occurrence: occurrenceRemarks: bottom trawl by the crew of Keelung-based fishing vessel Jing yang; recordedBy: Ming-Chih Huang; sex: female; lifeStage: adult; reproductiveCondition: embryos; preparations: whole animal; associatedSequences: Gene Bank: PP 715924, PP 719188; occurrenceID: 6776C362-B2F0-5C41-9E0F-14C6D66A1A28; Taxon: scientificName: Bathynomus paracelensis ; kingdom: Animalia; phylum: Arthropoda; class: Malacostraca; order: Isopoda ; family: Cirolanidae ; genus: Bathynomus ; Location: waterBody: South China Sea; islandGroup: Paracel Islands; island: Paracel Island; country: Taiwan; countryCode: Taiwan / TW; county: Taiwan; verbatimDepth: 300-550 m; minimumDepthInMeters: 300; maximumDepthInMeters: 550; verbatimLatitude: 19.08333 N; verbatimLongitude: 115.25 E; Identification: identifiedBy: Ming-Chih Huang; Geological context: earliestEraOrLowestErathem: miocene; Event: eventDate: 2023-1 - 28; startDayOfYear: 2023; year: 2023; month: 1; day: 28; habitat: continental slope; Record Level: type: PhysicalObject; modified: 2023-01 - 28; language: en; rightsHolder: National Museum of Marine Biology, Checheng, Taiwan; accessRights: not-for-profit use only; bibliographicCitation: Bathynomus paracelensis ( NMMB-CD 006302 ) for a specimen; institutionCode: National Museum of Marine Biology (NMMB); basisOfRecord: PreservedSpecimen GoogleMaps

Description

Ovum and samples Two ovigerous individuals ( NMMB-CD 006299 -006302). Ovum 12-15 mm in diameter (Fig. 1 View Figure 1 ), slightly oval, transparent to white, without a hard shell and the soft membrane gelatinous. Some samples may be incomplete due to bottom trawl capture. The right pereonites 5-6 of NMMB-CD 006299 are incomplete, the head of NMMB-CD 006301 is cracked and the shapes of NMMB-CD 006300 and NMMB-CD 006302 are complete; see Table 1 for detailed data.

Female holotype (singular numbers NMMB-CD 006300 , NCBI Accession No. PP 715922 for COI, Fig. 1 View Figure 1 and Fig. 2 View Figure 2 A). Body sub-parallel, coarsely punctate, without sculpting (Fig. 2 View Figure 2 A), total length (220 mm) approximately 2.2 times as long as maximal width (101 mm) (Fig. 1 View Figure 1 and Fig. 2 View Figure 2 A). Cephalon (Fig. 3 View Figure 3 A) without rostral process; eyes lateral, not visible in dorsal view (Fig. 2 View Figure 2 B and E). Head with ridge above eyes discontinuous (Fig. 2 View Figure 2 B). Frontal lamina triangular, obscured in ventral view, joining cephalon, separating antennular bases; clypeus sessile, with prominent longitudinal carina, ventral margins almost straight, dorsally triangular (Fig. 2 View Figure 2 C); clypeal region distal margin slightly concave; lateral margins parallel; apex narrowly round; apex angle obtuse (about 105 degrees).

Antennula peduncle 4 - articulate (Fig. 4 View Figure 4 F), with a tiny lobe at the end of peduncular article 3 (Fig. 4 View Figure 4 F, lobe); articles 1 and 2 articulated; article 2 as long as article 1; articles 3 and 4 almost as long as combined lengths of articles 1 and 2; peduncle articles 1-3 almost equal in length; flagellum longer than peduncle, multi-articulate, of approximately 30 articles. Antenna peduncle 4 - articulate (Fig. 4 View Figure 4 H), article 4 three times as long as wide, 1.2 times as long as article 3; article 2 the same length as article 1 (Fig. 4 View Figure 4 H); flagellum longer than peduncle and extending to the end of pleonite 2 (Fig. 2 View Figure 2 D and Fig. 3 View Figure 3 A), each section of flagellum article is longer than articles of antennula, composed of approximately 60 articles.

Mandibles (Fig. 6 View Figure 6 D), symmetrical. Incisor process of the mandible with 3 prominent black keratinised teeth on anterolateral margin (Fig. 6 View Figure 6 C); palp 3 - articulate, not reaching to incisor margin (Fig. 6 C). Maxilla with long setae (Fig. 6 E); lateral lobe with 11 keratinised spines, 2 small individual RS, 4 RS on medial lobe (Figs. 6 E and F). Maxilliped palp (Figs. 6 A and B) articles broad, wider than their articulating junctions, terminal article triangular, maxilliped endite cylindrical, with rounded distal end; medial margin provided with 5 coupling hooks.

Pereonite 1 distinctly longer than other pereonites, all coxae visible in dorsal view, all with oblique carina. Coxa of pereonite 7 distally broadened and slightly curved posteriorly (Fig. 2 View Figure 2 A, Fig. 3 View Figure 3 A and E).

Pereopod 1 basis 3.2 times as long as greatest width; ischium 0.43 times as long as basis, bearing 2 posteroproximal RS and 1 RS on posterodistal margin; merus with 7 short RS on anterodistal angle, proximal row of 3 RS on posterolateral margin; carpus inferior distal margin with 3 RS; propodus approximately 2.3 times as long as maximal width, posterior margin with 5 RS (Fig. 4 View Figure 4 A), dactylus 0.52 times as long as propodus. Pereopod 2 (Fig. 4 View Figure 4 B) ischium with 2 RS each on posterior and posterodistal margins; merus with 10 short RS on anterodistal angle, posteromedial margin with 3 RS in proximal row and 3 RS in distal row: propodus approximately 2.2 times as long as maximal width, with 4 RS on posterior margin (Fig. 4 View Figure 4 B). Pereopods 3 with anterodistal margin of merus strongly produced. Pereopods 4-6 similar, becoming progressively longer towards the posterior; Pereopod 4 intermediate between Pereopod 3 and Pereopod 5. Pereopod 6 similar to pereopod 7. Pereopod 7 (Fig. 4 View Figure 4 D) basis 3.8 times as long as greatest width, superior margin convex, inferior margin with 5 palmate setae; ischium 0.58 times as long as basis, superior distal angle with 8 RS, inferior distal angle with 6 RS; merus 0.65 as long as ischium, 1.4 times as long as wide, superior distal angle with 13 RS, inferior distal angle with 8 RS; carpus 0.75 as long as ischium, 1.2 times as long as wide, inferior margin with 2 RS, superior distal angle with 10 RS, inferior distal angle with 11 RS; propodus 0.95 as long as ischium, 4.75 times as long as wide, inferior margin with 4 RS (as 1 + 2 + 1), superior distal angle with 1 RS, inferior distal angle with 6 RS; dactylus 0.42 as long as propodus.

Oostegites arising from proximal parts of pereopods 1-6 (coxae) (Fig. 4 View Figure 4 E).

Pleon (88 mm) approximately 43 % of body length (220 mm) (Fig. 2 View Figure 2 A and Fig. 3 View Figure 3 A). Pleon as wide as pereon (Fig. 1 View Figure 1 and Fig. 2 View Figure 2 A); pleonite 1 with lateral margins not produced; pleonite 2 with lateral margins produced, posterolateral angles of pleonites 3–4 reaching to almost same level posteriorly (Fig. 2 View Figure 2 A and Fig. 3 View Figure 3 A). Pleonite 3 not extending beyond pleonite 5 (Fig. 3 View Figure 3 A). Posterolateral angle of pleonites 3 and 4 extending to pleonite 5 posterior margin (Fig. 2 View Figure 2 A and Fig. 3 View Figure 3 A).

Pleopods (Fig. 3 View Figure 3 E and Fig. 5 View Figure 5 A-D) with respiratory branchiae on dorsal and ventral surfaces of all endopods, except only ventrally on pleopod 1. Pleopods translucent, granular-surfaced film (Fig. 5 View Figure 5 ). Pleopod 1 (Fig. 5 View Figure 5 A and B) exopod 1.86 times as long as wide, lateral margin straight, distally vast rounded, mesial margin strongly convex; endopod 1.52 times as long as vast, distally broadly rounded, lateral margin sinuate. Pleopod 2 (Fig. 5 View Figure 5 C and D) slightly small than pleopod 1 appearing subtriangular.

Uropodal rami not extending beyond pleotelson (Fig. 2 View Figure 2 A and Fig. 3 View Figure 3 B), peduncle with 2 ventrolateral RS: exopod and endopod with sinuate lateral and distal margins; exopod lateral margin sinuate, setal fringe of medium length (approximately 65 %), with 4 RS, mesial margin straight (Fig. 3 View Figure 3 C and D), distomesial margin rounded, distal margins with 4 RS, distolateral angle slightly produced, subacute; endopod lateral margin sinuate, with 3 RS, mesial margin straight (Fig. 3 View Figure 3 C and D), distomedial angle rounded, distal margin slightly sinuate, with 9 RS, distolateral corner slightly produced, subacute (Fig. 2 View Figure 2 A, Fig. 3 View Figure 3 C and D). Pleotelson (43 mm) approximately 20 % of body length, approximately 0.52 as long as wide, dorsal surface granular, with median carina; posterior margin with 11 stout, almost straight spines, plus 2 small lateral spines, others subequal, central spine not bifid; marginal setae present between spines (Fig. 2 View Figure 2 A and E).

Diagnosis

Body shape sub-parallel (Fig. 1 View Figure 1 and Fig. 2 View Figure 2 A), body size medium, clypeus apex narrowly round, clypeus apex obtuse angle (Fig. 2 View Figure 2 C), five of maxilliped endite coupling (Fig. 6 View Figure 6 A and B), 11 of maxillula keratinised spine (Fig. 6 View Figure 6 E and F), 12 or 13 almost straight pleotelson spines (Fig. 2 View Figure 2 A, E and Fig. 3 View Figure 3 B), uropodal endopod distolateral corner slightly produced, subacute (Fig. 3 View Figure 3 B, C and D), uropodal exopod distolateral corner slightly produced, subacute (Fig. 3 View Figure 3 B, C and D), RS of uropodal endopod distributed near distomedial corner (Fig. 3 View Figure 3 B, C and D)

Note

The difference between B. paracelensis sp. nov. and B. jamesi includes body length (average 220 mm vs. 323 mm, Table 3 View Table 3 ), body shape (sub-parallel vs. ovate), clypeus lateral margins (parallel vs. concave), number of maxillula keratinised spine (11 vs. 9) and pleotelson spines shape (almost straight vs. upwardly curved). In B. paracelensis sp. nov. uropodal endopod, the anterolateral margin ends in a small tooth and the distal margin is convex. In B. jamesi , the anterolateral margin ends at a right angle and the distal margin is truncated.

The differences between B. paracelensis sp. nov. and B. vaderi include body length (average 220 mm vs. 279 mm), body shape (sub-parallel vs. ovate), clypeus apex shape (narrowly round vs. narrowly subacute), clypeus apex angle (obtuse angle vs. acute angle), number of maxilliped endite coupling hooks (5 vs. 4), number of maxillula keratinised spines (11 vs. 9) and pleotelson spines shape (almost straight vs. upwardly curved).

In B. paracelensis sp. nov. uropodal endopod, RS is mainly distributed in the distomedial margin of the endopod distal margin, with little or no RS distribution distolateral (Fig. 3 View Figure 3 C and D). This differs from B. jamesi or B. vaderi , where RS is evenly distributed in the endopod distal margin. However, this phenomenon does not exist in exopod. In addition, B. paracelensis sp. nov. is darker than B. jamesi and B. vaderi and closer to B. doederleini in body colour.

Variation

Specimens ( NMMB-CD 006299 -006302): variation appears in body length / width ratio (2.16-2.26), pleotelsonic length / width ratio (0.51-0.62) and number of pleotelsonic spines (12 or 13) (Table 1 View Table 1 ). The smallest body length / width ratio is NMMB-CD 006301 (2.16). On the other hand, NMMB-CD 006299 with the largest (2.26). The pleotelsonic length / width ratio is also different, with NMMB-CD 006299 being the largest at 0.62 and NMMB-CD 006300 being the smallest at 0.51. Most of the number of pleotelsonic spines is 13, but for NMMB-CD 006301 , it is 12 (Table 1).

Molecular biology

Amplified PCR products of 518 bp from COI and 508 bp from 16 S rRNA, respectively, were obtained for the COI and 16 S rRNA nucleotide sequences of four specimens B. paracelensis sp. nov. ( NMMB-CD 006299 -006302), respectively (Fig. 7 View Figure 7 , Fig. 8 View Figure 8 and Table 1 View Table 1 ). The results of COI and 16 S rRNA alignments showed that samples collected from the Paracel Islands are various from B. jamesi and B. doederleini (Fig. 7 View Figure 7 and Fig. 8 View Figure 8 ). The sequence data have been submitted to DDBJ / EMBL / GenBank on 28 April 2024 (New Paracel Bathynomus (NPB) , Accession Nos. PP 715921 (NPB 1, NMMB-CD 006299 ), PP 715922 (NPB 2, NMMB 006300 ), PP 715923 (NPB 3, NMMB-CD 006301 ) and PP 715924 (NPB 4, NMMB-CD 006302 ) for COI and PP 719187 (NPB 1, NMMB-CD 006299 ), PP 719190 (NPB 2, NMMB-CD 006300 ), PP 719189 (NPB 3, NMMB-CD 006301 ) and PP 719188 (NPB 4, NMMB-CD 006302 ) for 16 S rRNA. The four individuals are identical in the analysed 518 - bp COI gene sequences (Fig. 7 View Figure 7 ) and 508 bp (Fig. 8 View Figure 8 , only 345 bp are shown). The COI sequences of the four individuals are all the same. On the other hand, 16 S rRNA sequences also show a high degree of identity, with only one base pair variation in the 508 - bp 16 S rRNA gene sequences. This base pair variation exists in sample NMMB-CD 006299 at position ca. 270 G> A (PP 719187) (Fig. 8 View Figure 8 ).

The COI s sequence of all Bathynomus species currently submitted in the NCBI database is used for DNA sequence comparison. Species include B. kensleyi ( MZ 723938 View Materials ), B. jamesi ( KX 417647 View Materials ), B. yucatanensis ( MZ 354630 View Materials ), B. giganteus ( MG 229639 View Materials ), B. maxeyorum ( KT 963292 View Materials ), B. kapala (OQ 970652), and B. doederleini ( MZ 723938 View Materials ). The comparison results show that the differences between B. paracelensis sp. nov. and other species are as follows: B. kensleyi (65 bases different, base different ratios 12.5 %), B. jamesi (70, 13.5 %), B. yucatanensis (74, 14.3 %), B. giganteus (66, 12.7 %), B. maxeyorum (75, 14.5 %), B. kapala (89, 17.2 %) and B. doederleini (101, 19.5 %). It can be seen from the base that there are different ratios of more than 12.5 %, indicating that it may not be the same species.

On the other hand, 16 S rRNA sequences (345 bp) are also compared. Results with a high rate of variation can be obtained (Fig. 8 View Figure 8 ). The comparison results show that the differences between B. paracelensis sp. nov. and other species are as follows: B. kensleyi (37, 10.7 %), B. jamesi (32, 9.3 %), B. yucatanensis (34, 9.9 %), B. giganteus (31, 9.0 %), B. kapala (55, 15.9 %) and B. doederleini (55, 15.9 %).

After COI and 16 S rRNA sequencing and comparison with an NCBI databank, the results confirmed that four specimens were all new sequences and the sequences do not exist in the NCBI database.

Etymology

The epithet is an adjective derived from the name of the nearest island to the point of collection, the Paracel Islands. The Japanese name: Seisagusokumushi.

Distribution

The samples were captured in the South China Sea and the closest island is Paracel Island.

Taxon discussion

The clypeus of Bathynomus is polymorphic, including lateral margins that are parallel or concave, distal margins that are straight or concave and an apex shape and angle. B. paracelensis sp. nov. exhibits an obtuse angle in the apex (about 105 degrees) (Fig. 2 View Figure 2 C is very different from the acute angle in B. vaderi (about 70 degrees) ( Ng et al. (2025), figs. 5 C and 6 C). In addition, there is also a difference in whether the ends of the lateral margins on both sides are sharp. It is sharp in B. vaderi ( Ng et al. 2025) , but not in B. paracelensis sp. nov. and B. jamesi . The clypeus distal margin appears serrated in B. paracelensis sp. nov., while B. jamesi appears smooth and B. vaderi has a few serrated margins.

Uropodal endopod differences can be found between B. paracelensis sp. nov. and B. jamsei . In B. paracelensis sp. nov., the anterolateral margin ends in a slight tooth and the distal margin is convex (Fig. 3 View Figure 3 B, C and D). In B. jamesi , the anterolateral margin ends at a right angle and the distal margin truncates ( Huang et al. (2022), figs. 4 d and e).

The distribution of RS in the uropodal endopod distal margin is also very special, unlike the distribution of B. jamesi ( Huang et al. (2022), figs. 4 d and e) and B. vaderi ( Ng et al. (2025), figs. 8 d and e). B. paracelensis sp. nov. is distributed near the distomedial corner (Fig. 3 View Figure 3 C and D).

Pleotelson spines are straight or upwardly curved. Lowry and Dempsey (2006) recorded that only B. kensleyi and B. lowryi have upward curves, but now B. jamesi ( Huang et al. 2022) and B. vaderi ( Ng et al. 2025) have been added. Pleotelson spines in B. paracelensis sp. nov. are slightly upwardly curved, but not as much as in B. jamesi and B. vaderi (Fig. 2 View Figure 2 E).

In B. doederleini and B. affinis , the number of maxilulla lateral lobe with 11 keratinised spines ( Shih (1972), figs. 3 and 4). However, the maxilulla spines of B. jamesi are only nine ( Huang et al. (2022), fig. 7 e).

The number of maxilulla spines is also one of the classified items. The earliest classification of maxilulla spine was B. decemspinosus ( Shih 1972) and its scientific name is the number of maxilulla spines. In B. paracelensis sp. nov., the number of maxilulla lateral lobes is with 11 keratinised spines (Fig. 6 View Figure 6 E and F), but in B. vaderi , there are only nine ( Ng et al. 2025, fig. 7 e). The number of maxilliped endite coupling hooks also differs in Bathynomus species, with five in B. paracelensis sp. nov. (Fig. 6 View Figure 6 A and B). B. jamesi also has five roots ( Huang et al. (2022), fig. 7 b), but in B. vaderi , there are only four ( Ng et al. (2025), fig. 7 b).