Shinkailepas gigas Chen, Watanabe & Tsuda, 2024

(SOSA), Senckenberg Ocean Species Alliance, Brandt, Angelika, Chen, Chong, Engel, Laura, Esquete, Patricia, Horton, Tammy, Jażdżewska, Anna M., Johannsen, Nele, Kaiser, Stefanie, Kihara, Terue C., Knauber, Henry, Kniesz, Katharina, Landschoff, Jannes, Lörz, Anne-Nina, Machado, Fabrizio M., Martínez-Muñoz, Carlos A., Riehl, Torben, Serpell-Stevens, Amanda, Sigwart, Julia D., Tandberg, Anne Helene S., Tato, Ramiro, Tsuda, Miwako, Vončina, Katarzyna, Watanabe, Hiromi K., Wenz, Christian & Williams, Jason D., 2024, Ocean Species Discoveries 1 – 12 — A primer for accelerating marine invertebrate taxonomy, Biodiversity Data Journal 12, pp. e 128431-e 128431 : e128431-

Shinkailepas gigas Chen, Watanabe & Tsuda sp. nov.

Shinkailepas sp. nov. – Giguère and Tunnicliffe (2021): table S 5

Shinkailepas sp. Manus Basin / Mariana Volcanic Arc – Poitrimol et al. (2022): fig. 6

Materials

Type status: Holotype. Occurrence: catalogNumber: SMF 373153 ; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; sex: male; lifeStage: adult; preparations: fixed and preserved in 10 % buffered formalin; occurrenceID: E8CBFB26-01DB-5085-8071-20E65C686665; Taxon: scientificName: Shinkailepas gigas Chen, Watanabe & Tsuda ; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida ; family: Lepetodrilidae ; genus: Shinkailepas ; specificEpithet: gigas ; taxonRank: species; scientificNameAuthorship: Chen, Watanabe & Tsuda; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; waterBody: Western Pacific Ocean; islandGroup: Northern Mariana Islands; country: United States of America; locality: Northwest Eifuku Volcano vent field, near Champagne vent ; verbatimDepth: 1615 m; verbatimLatitude: 21 ° 29.2383 ' N; verbatimLongitude: 144 ° 02.4937 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 213; eventDate: 07 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: SMF; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: NSMT-Mo 79486 ; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; sex: male; lifeStage: adult; preparations: fixed and preserved in 10 % buffered formalin; occurrenceID: 1A32DE7D-9C5D-5C5F-8058-0CB78A9C00D9; Taxon: scientificName: Shinkailepas gigas Chen, Watanabe & Tsuda ; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida ; family: Lepetodrilidae ; genus: Shinkailepas ; specificEpithet: gigas ; taxonRank: species; scientificNameAuthorship: Chen, Watanabe & Tsuda; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; waterBody: Western Pacific Ocean; islandGroup: Northern Mariana Islands; country: United States of America; locality: Northwest Eifuku Volcano vent field, near Champagne vent ; verbatimDepth: 1615 m; verbatimLatitude: 21 ° 29.2383 ' N; verbatimLongitude: 144 ° 02.4937 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 213; eventDate: 07 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: NSMT; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: SMF 373154 ; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; sex: female; lifeStage: adult; preparations: 99 % EtOH; occurrenceID: 495CC54B-399F-5D22-B3FB-D3A5C9DC141D; Taxon: scientificName: Shinkailepas gigas Chen, Watanabe & Tsuda ; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida ; family: Lepetodrilidae ; genus: Shinkailepas ; specificEpithet: gigas ; taxonRank: species; scientificNameAuthorship: Chen, Watanabe & Tsuda; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; waterBody: Western Pacific Ocean; islandGroup: Northern Mariana Islands; country: United States of America; locality: Northwest Eifuku Volcano vent field, near Champagne vent ; verbatimDepth: 1615 m; verbatimLatitude: 21 ° 29.2383 ' N; verbatimLongitude: 144 ° 02.4937 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 213; eventDate: 07 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: SMF; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: MNHN-IM- 2019-34808 ; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; sex: female; lifeStage: adult; preparations: 99 % EtOH; occurrenceID: 9C442EE1-49C3-52F5-B984-DD998283F040; Taxon: scientificName: Shinkailepas gigas Chen, Watanabe & Tsuda ; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida ; family: Lepetodrilidae ; genus: Shinkailepas ; specificEpithet: gigas ; taxonRank: species; scientificNameAuthorship: Chen, Watanabe & Tsuda; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; waterBody: Western Pacific Ocean; islandGroup: Northern Mariana Islands; country: United States of America; locality: Northwest Eifuku Volcano vent field, near Champagne vent ; verbatimDepth: 1615 m; verbatimLatitude: 21 ° 29.2383 ' N; verbatimLongitude: 144 ° 02.4937 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 213; eventDate: 07 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: MNHN; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: NSMT-Mo 79487 ; occurrenceRemarks: fragmented specimen; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; lifeStage: adult; preparations: 99 % EtOH; associatedSequences: https://www.ncbi.nlm.nih.gov/nuccore/OR640971; occurrenceID: AD20F976-B32C-5B4A-AA92-A050891CEB37; Taxon: scientificName: Shinkailepas gigas Chen, Watanabe & Tsuda ; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida ; family: Lepetodrilidae ; genus: Shinkailepas ; specificEpithet: gigas ; taxonRank: species; scientificNameAuthorship: Chen, Watanabe & Tsuda; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; waterBody: Western Pacific Ocean; islandGroup: Northern Mariana Islands; country: United States of America; locality: Northwest Eifuku Volcano vent field, near Champagne vent ; verbatimDepth: 1615 m; verbatimLatitude: 21 ° 29.2383 ' N; verbatimLongitude: 144 ° 02.4937 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 213; eventDate: 07 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: NSMT; basisOfRecord: PreservedSpecimen

Description

Shell (Fig. 6 ): limpet form as adult with evidence of tighter coiling when juvenile, very large for genus. Shell dimensions of the holotype and paratypes are given in Table 3 . Aperture oval, clear ventral columellar deck present posteriorly. Apex very posterior, protruding beyond posterior shell edge, slightly recurved to right side. Shell sculpture (Fig. 7 C) finely cancellate with concentric ribs slightly stronger than radial ribs, minor protuberances occur where two ribs cross. Lateral profile of shell strongly curved. Shell microstructure (Fig. 7 D) consisting of four layers: thin outermost dense homogenous layer followed by another thin granular homogenous layer which transitions to thick complex crossed lamellar layer then finally to thin simple prismatic layer. Protoconch corroded in all five adult specimens available for study.

External anatomy typical for the genus. Head large, broad, snout wide. Cephalic tentacles moderate in length. Males exhibit one large, swollen penis (Fig. 6 A) just anterior of right cephalic tentacle. Mouth circular, oral disc papillated, oral lobes very large in size, extending laterally. Pallial margin swollen, simple, without tentacles. Foot circular, posterior half of epipodial fold serrated into approximately 50 paddle-like, broad projections. Operculum lacking in all five adults available for study.

Radula (Fig. 7 A – B) rhipidoglossate, formula ca. 70-4 - 1 - 4 - ca. 70. Central tooth tall trapezoid, shaft thin, film-like, weakly developed with broad overhanging cusp, cutting edge smooth. Innermost laterals enlarged, three times as broad as rachidian, oblique in outline, shaft film-like; anterior edge rolled to form simple cusps lacking any serration. Second lateral narrower than rachidian, shaft sickle-like, with double overhanging cusps, upper cusp lacking serration, lower cusp shallowly serrated into about 10 cusps. Third lateral of similar breath to rachidian, twice as long as second lateral, cusp deformed, outer edge of shaft carrying broad lateral extension rolled inwards. Outermost lateral twice as large as third lateral, shaft divided into two columns, fusing anteriorly into one broad overhanging, simple cusp lacking serration. Inner marginals with semi-circular cusps serrated into 4-8 cusps, becoming more deeply serrated outwards. Outer marginals becoming much smaller in size with cusps serrated into several long denticles, gradually decreasing in size outwards.

Diagnosis

A very large Shinkailepas species up to 23 mm in shell length with apex bent to the right side and protruding beyond the posterior shell margin. Shell sculpture finely cancellate, with concentric ribs only slightly stronger than radial ones.

Etymology

The specific epithet gigas is Greek for ‘ giant’; referring to the relatively large size of the species. Used as noun in apposition.

Distribution

Specimens of S. gigas Chen, Watanabe & Tsuda , sp. nov. with identities confirmed by COI barcoding have been collected from the hydrothermal vents on Northwest Eifuku and Northwest Rota volcanoes on Mariana Arc ( Giguère and Tunnicliffe 2021) and the Susu vent field in Manus Basin ( Poitrimol et al. 2022).

Taxon discussion

Previously available COI sequences of this species include one from Northwest Eifuku ( MW 807775 ) and one from Northwest Rota ( MW 807774 ), Mariana Arc published by Giguère and Tunnicliffe (2021), as well as two from Susu vent field, Manus Basin ( OM 264371 - OM 264372 ) published by Poitrimol et al. (2022). One new COI sequence was generated for this work from paratype 4 (NSMT-Mo 79487) and deposited in GenBank under the accession number OR 640971. We did not examine specimens sequenced by Giguère and Tunnicliffe (2021) or Poitrimol et al. (2022), but their COI sequences are highly similar to ours with the uncorrected pairwise percentage genetic similarities being 99.3 % or above across all pairs.

Shinkailepas gigas Chen, Watanabe & Tsuda , sp. nov. was already recognised as an undescribed species by Giguère and Tunnicliffe (2021). Molecular phylogenetic reconstruction using the COI gene by Poitrimol et al. (2022) confirmed its genetic distinctness from described Shinkailepas species, but it remained unnamed until now. Its most closely related known species, Poitrimol et al. (2022), is Shinkailepas kaikatensis Okutani, Saito & Hashimoto, 1989 with a known distribution from vents on the Izu-Ogasawara Arc (Kaikata Seamount and Myojin Knoll), Okinawa Trough (Yoron Hole) and Mariana Arc (Kasuga 2 Seamount and East Diamante Seamount) ( Fukumori et al. 2019). Though S. kaikatensis and S. gigas sp. nov. have, so far, not been sampled from the same vent fields, their distribution ranges overlap on the Mariana Arc and could potentially occur sympatrically. Although neither Giguère and Tunnicliffe (2021) nor Poitrimol et al. (2022) applied particular species delimitation tools, their distinctness is supported by a lowest known uncorrected COI genetic distance of 4.2 % ( Poitrimol et al. 2022). Morphologically, S. gigas n. sp. is clearly distinct from other named Shinkailepas species including S. kaikatensis by combining the following morphological features: 1) a finely cancellate sculpture where concentric ribs are slightly stronger than radial ones; 2) a very posterior apex bending slightly to the right and protruding beyond the posterior shell edge and 3) a very large size ( Okutani et al. 1989, Sasaki et al. 2003, Fukumori et al. 2019). The only described congener with comparable size and sculpture is S. conspira Beck in Chen & Sigwart, 2023, but the apex of S. conspira is more anterior and central compared to S. gigas sp. nov. ( Chen and Sigwart 2023). Furthermore, the central and inner laterals in S. gigas sp. nov. are exceptionally weakly developed for the genus. In all five adult specimens of S. gigas sp. nov. the operculum was lacking and, therefore, the juvenile operculum is likely naturally lost in this species during growth.

Notes

Methods

As for Lepetodrilus marianae Chen, Watanabe & Tsuda , sp. nov., including the type specimen repositories SMF, NSMT and MNHN. Gastropods were collected near Champagne vent ( Tunnicliffe et al. 2009), Northwest Eifuku Volcano vent field (21 ° 29.2383 ' N, 144 ° 02.4937 ' E), 1615 m depth, collected by suction sampler mounted on ROV KM-ROV dive # 213, 2023 / iii / 07, R / V KAIMEI cruise KM 23-05. Genetic barcoding of the mitochondrial cytochrome c oxidase subunit I ( COI) gene was conducted using the universal primer pair HCO 2198 / LCO 1490 ( Folmer et al. 1994) following Chen et al. (2021).

Figures

Figure 6. Shinkailepas gigas Chen, Watanabe & Tsuda, sp. nov., habitus photographs of representative type specimens. A. holotype (SMF 373153), dorsal, ventral and lateral views, arrowhead on ventral view indicates the penis; B. Paratype 1 (NSMT-Mo 79486), dorsal, ventral and lateral views; C. Paratype 2 (SMF 373154), dorsal and ventral views; D. Paratype 3 (MNHN-IM- 2019-34808), dorsal and ventral views. Scale bars: 5 mm.

Figure 7. Shinkailepas gigas Chen, Watanabe & Tsuda, sp. nov., scanning electron micrographs of paratype 4 (NSMT-Mo 79487). A. Radula overview; B. Close-up of marginal teeth; C. Shell sculpture; D. Fractured cross section of a shell showing microstructure. Scale bars: 500 μm (A, C), 50 μm (B, D).