Lepetodrilus marianae Chen, Watanabe & Tsuda sp. nov.

Lepetodrilus aff. schrolli MT: Johnson et al. (2008): fig. 1, table 2; Giguère and Tunnicliffe (2021): table 2

Lepetodrilus aff. schrolli Mariana Trough: Poitrimol et al. (2022): fig. 2 A

Materials

Type status: Holotype. Occurrence: catalogNumber: SMF 373150; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; sex: female; lifeStage: adult; preparations: 99 % EtOH; occurrenceID: 54FC6400-9086-515C-9A40-FF588BC6160E; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 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 79482; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; sex: male; lifeStage: adult; preparations: 99 % EtOH; occurrenceID: 29F12B98-B99E-514F-A9F1-A17B77E9B9C9; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: NSMT; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: NSMT-Mo 79483; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; sex: female; lifeStage: adult; preparations: fixed and preserved in 10 % buffered formalin; occurrenceID: 9D0216B3-C5D4-5E6A-88AB-C7F8B24BD463; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: NSMT; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: MNHN-IM- 2019-34806; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; lifeStage: adult; preparations: 99 % EtOH; occurrenceID: E4CBEB40-C841-5405-BC70-6E59179B58E8; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: MNHN; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: MNHN-IM- 2023-431; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; lifeStage: adult; preparations: fixed and preserved in 10 % buffered formalin; occurrenceID: 34525B69-92DA-5441-B18A-7E22198C73D4; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: MNHN; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: SMF 373151; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 1; lifeStage: adult; preparations: fixed and preserved in 10 % buffered formalin; occurrenceID: E0369298-32C6-556A-825E-4A4F51164311; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: SMF; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: SMF 373152; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 5; lifeStage: growth series; preparations: 99 % EtOH; occurrenceID: C0511CEB-4708-55D3-B60C-ECF23380473A; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 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 79484; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 5; lifeStage: growth series; preparations: 99 % EtOH; occurrenceID: 18D8E94F-2DC7-5B47-9FDC-4BE5D33EF30A; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: NSMT; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: MNHN-IM- 2019-34807; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: 5; lifeStage: growth series; preparations: 99 % EtOH; occurrenceID: 7DC6CE20-ACE6-5F45-BC6C-083947555E92; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: MNHN; basisOfRecord: PreservedSpecimen

Type status: Other material. Occurrence: catalogNumber: NSMT-Mo 79485; recordedBy: R / V KAIMEI cruise KM 23-05; individualCount: about 50; preparations: 99 % EtOH, - 80 ° C; associatedSequences: https://www.ncbi.nlm.nih.gov/nuccore/OR640969 | https://www.ncbi.nlm.nih.gov/nuccore/OR640970; occurrenceID: FF29D3D8-D51C-580F-BA53-BF26335C9C19; Taxon: scientificName: Lepetodrilus marianae Chen, Watanabe & Tsuda; kingdom: Animalia; phylum: Mollusca; class: Gastropoda; order: Lepetellida; family: Lepetodrilidae; genus: Lepetodrilus; specificEpithet: marianae; 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: 1660 m; verbatimLatitude: 21 ° 29.2506 ' N; verbatimLongitude: 144 ° 02.4498 ' E; Event: samplingProtocol: suction sampler mounted on ROV KM-ROV, dive # 223; eventDate: 25 / 03 / 2023; habitat: white bacterial mats on rocks around diffuse flow venting; Record Level: institutionCode: NSMT; basisOfRecord: PreservedSpecimen

Description

Shell (Fig. 4): very loosely coiled, juvenile shell becomes limpet-shaped in adult stages. Medium-sized for genus, aperture oval, maximum shell length around 8.5 mm. Shell dimensions of the holotype and paratypes 1–5 are given in Table 2. Apex at posterior end of shell (Fig. 4 A) or protruding beyond it (Fig. 4 C) depending on substrate morphology, also influencing shell height. Fine concentric ribs (Fig. 5 C) present across all growth stages, adults developing broad, strongly raised concentric ridges to give strongly undulated profiles (Fig. 4 A-F, see lateral views); strength and frequency of latter ridges varying amongst individuals. Shell microstructure (Fig. 5 D) with thin outer homogenous layer and thick inner complex crossed lamellar layer, numerous fine shell pores are presented perpendicular to shell surface. Protoconch (Fig. 5 B) indistinctly coiled, approximately 170 μm in diameter. Protoconch sculpture corroded and indiscernible on all specimens investigated. Periostracum light green, smooth, moderately thick, enveloping edge of shell.

External anatomy (Fig. 4 A – C) overall typical for Lepetodrilus. Oval foot, muscle scar horseshoe-shaped, left arm longer than right arm. Cephalic tentacles simple, conical, extending from broad base. Eyes lacking. Penis in males simple conical with narrow base, tapering to blunt tip, seminal groove on dorsal side. Two pairs of epipodial tentacles present on posterior end of foot, simple conical with broad base. Mantle edge with two folds, outer fold thin, extending to edge of periostracum; inner fold thick, densely lining with (presumably sensory) small tentacles. Operculum lacking.

Radula (Fig. 5 A) rhipidoglossate, formula ca. 25-5 - 1 - 5 - ca. 25. Central (rachidian) tooth low with broad shaft carrying one lateral ridge on either side, rapidly tapering to single narrow, pointed cusp with smooth cutting edges. Innermost lateral (‘ 1 ’, Fig. 5 A) twice as broad as central tooth, with slanted, very broad overhanging cusp only carrying very weak serrations on outermost one-third. Three middle laterals (‘ 2–4 ’, Fig. 5 A) narrower, of similar breadth to central tooth, carrying simple triangular overhanging cusps, inner edges carrying weak serrations, outer edges smooth. Outermost lateral (‘ 5 ’, Fig. 5 A) much broader again, with triangular overhanging cusp carrying weak serrations on inner edge plus strong serrations on outer edge. Marginals with very elongated shafts ending in spoon-like cusps finely serrated into about 20 denticles, innermost denticle strongest by far. Size of marginals decrease gradually outwards.

Diagnosis

A medium-sized Lepetodrilus with two types of concentric sculpture: regular, fine concentric ribs across all growth stages and irregular, strongly raised concentric ridges in adults. Apex at the posterior end of shell or overhanging it.

Etymology

The specific epithet marianae is a noun in the genitive case, after the species distribution range in Mariana Arc and Mariana Trough. This species was amongst many western Pacific vent gastropods first recognised as new by the late German malacologist Lothar A. Beck (Chen and Sigwart 2023). During the course of searching for unpublished material and manuscript by Beck (see Chen and Sigwart (2023)), we came across unpublished writing by Beck and his former student Kathrin Sobjinski suggesting the specific epithet marianae for this species, which we have decided to honour.

Distribution

Specimens of L. marianae Chen, Watanabe & Tsuda, sp. nov. have been collected at several hot vent fields in both Mariana Arc (northwest Eifuku, northwest Rota, Seamount X) and Mariana Trough (Alice Springs, Illium, Burke, Hafa Adai, Perseverence, Forecast, Snail and Archaean), confirmed by COI sequences (Johnson et al. 2008, Giguère and Tunnicliffe 2021).

Taxon discussion

Lepetodrilus is a genus of vetigastropod limpets commonly found in hydrothermal vents globally. The first comprehensive molecular phylogenetic reconstruction of this genus using the COI gene by Johnson et al. (2008) revealed that Lepetodrilus inhabiting the south-western Pacific vents consisted of three cryptic species showing clear barcoding gaps, including L. schrolli L. Beck, 1993 from Manus Basin, ‘ Lepetodrilus aff. schrolli LF’ from Lau and Fiji Basins and ‘ Lepetodrilus aff. schrolli MT’ from Mariana Trough. Later, further sampling and sequencing of material from Mariana Arc by Giguère and Tunnicliffe (2021) revealed highly similar COI sequences to ‘ Lepetodrilus aff. schrolli MT’ (sensu Johnson et al. (2008)), extending its distribution to Mariana Arc vents including the Northwest Eifuku Volcano vent field (the type locality as per this work). Although Giguère and Tunnicliffe (2021) did not carry out a phylogenetic analysis using their sequences of this species (COI, MW 807763 - MW 807765; 18 S rRNA, MZ 128922 - MZ 128923), this was done by Poitrimol et al. (2022) using the COI gene which confirmed that the Mariana Trough sequences from Johnson et al. (2008) (EU 306431 - EU 306436) and the Mariana Arc sequences from Giguère and Tunnicliffe (2021) (MW 807763 - MW 807765) fall into the same species-level clade. In both abovementioned phylogenetic analyses, ‘ Lepetodrilus aff. schrolli MT’ (sensu Johnson et al. (2008)) was recovered sister to a clade containing L. schrolli and ‘ Lepetodrilus aff. schrolli LF’ (sensu Johnson et al. (2008)). The lowest uncorrected sequence divergence for the COI gene amongst these three species was 3.1 % (Johnson et al. 2008).

Lothar A. Beck attempted to describe these two Lepetodrilus species from the southwest Pacific, but they were never published before he passed away in 2020 (Chen and Sigwart 2023). Recently, many new species Beck recognised were formally published by Chen and Sigwart (2023), based on Beck’s unpublished manuscript, including ‘ Lepetodrilus aff. schrolli LF’ sensu Johnson et al. (2008) which is now Lepetodrilus fijiensis Beck in Chen & Sigwart, 2023. ‘ Lepetodrilus aff. schrolli MT’ (sensu Johnson et al. (2008)), however, remained undescribed until now and corresponds to Lepetodrilus marianae Chen, Watanabe & Tsuda, sp. nov. described herein. Although we were not able to study the previously sequenced specimens, we could examine Lepetodrilus specimens from NW Eifuku (Scripps Institution of Oceanography, Benthic Invertebrate Collection SIO-BIC M 18546) collected together with those sequenced in Giguère and Tunnicliffe (2021) and they agreed morphologically with L. marianae sp. nov. Two new COI sequences were generated for this work from two specimens in paratype series 7 (NSMT-Mo 79484) and deposited in GenBank under the accession numbers OR 640969 - OR 640970. All abovementioned sequences of L. marianae sp. nov. exhibited uncorrected pairwise genetic similarities above 99.2 %.

Morphologically, L. marianae sp. nov. can be easily distinguished from other described Lepetodrilus species by its strong concentric sculpture, including its closest relatives (Johnson et al. 2008) L. schrolli and L. fijiensis L. Beck in Chen & Sigwart, 2023 (Beck 1993, Chen and Sigwart 2023). The only other Lepetodrilus species with similar shell profile and concentric sculpture is L. concentricus Linse, Roterman & Chen, 2019 from Antarctic vents on the East Scotia Ridge, but L. concentricus only exhibits one type of sculpture intermediate in strength between the two types seen in L. marianae sp. nov. (Linse et al. 2019) and, therefore, they are morphologically distinct.

Notes

Methods

Gastropods were collected near Champagne vent (Tunnicliffe et al. 2009), Northwest Eifuku Volcano vent field (21 ° 29.2506 ' N, 144 ° 02.4498 ' E), 1660 m depth, using a suction sampler mounted on the remotely-operated vehicle (ROV) KM-ROV on-board R / V KAIMEI cruise KM 23-05. The animals were sieved on a 1 mm sieve using cold seawater and sorted into different morphospecies. Specimens were placed into 10 % buffered formalin or 99 % ethanol as soon as they were sorted. Dissections were done under a stereomicroscope (Olympus SZX 7). Investigation of the gross morphology and genetic barcoding of the mitochondrial cytochrome c oxidase subunit I (COI) gene were conducted using the Lepetodrilus - specific primer pairs LepetESR-F / LepetESR-R following Linse et al. (2019). Scanning electron microscopy was done using a Hitachi TM- 3000 table-top system at 15 kV. Shell microstructure terminology follows Kiel (2004). Specimens are deposited in Senckenberg Museum Frankfurt (SMF), National Museum of Nature and Science, Tsukuba (NSMT) or Muséum national d’Histoire naturelle, Paris (MNHN).