Veleropilina gretchenae Sigwart & Steger sp. nov.

Veleropilina cf. oligotropha (Rokop, 1972): Brandt (2022): 157, 165, Fig. 5.96, tab. 5.26

Veleropilina sp. Sigwart et al. (2025): table 1, fig. 4 B

Veleropilina sp. Chen et al. (2025): fig. 1, text

Materials

Type status: Holotype. Occurrence: catalogNumber: SMF 373808; recordedBy: R / V SONNE AleutBio cruise SO 293; individualCount: 1; lifeStage: adult; previousIdentifications: Veleroplina cf. oligotropha | Veleropilina sp.; associatedReferences: Brandt, A. (2022) (ed.) SO 293 AleutBio (Aleutian Trench Biodiversity Studies). SONNE-Berichte (R / V SONNE cruise reports). 209 pp.; occurrenceID: A8D84ADE-70F5-50BB-8363-96C3208E1D3D; Taxon: scientificName: Veleropilina gretchenae Sigwart & Steger; kingdom: Animalia; phylum: Mollusca; class: Monoplacophora; order: Neopilinida; family: Neopilinidae; genus: Veleropilina; specificEpithet: gretchenae; taxonRank: species; scientificNameAuthorship: Sigwart & Steger; nomenclaturalCode: ICZN; Location: higherGeography: Pacific Ocean; waterBody: Northeast Pacific Ocean, U. S. Exclusive Economic Zone, Alaska Region; locality: Aleutian Trench, S of Unalaska Island, AleutBio station SO 293 _ 9-16 AGT; verbatimDepth: 6465-6465 m; minimumDepthInMeters: 6465; maximumDepthInMeters: 6465; verbatimCoordinates: 51°55.94'N, 166°51.84'W to 51°55.94'N, 166°51.85'W; verbatimCoordinateSystem: degrees decimal minutes; Identification: identifiedBy: Julia D. Sigwart; Event: eventID: SO 293 _ 9-16 AGT; samplingProtocol: Agassiz trawl, contents sieved through a 1 mm mesh; samplingEffort: 990 m trawled distance; eventDate: 2022-08 - 18 T 05: 41 Z / 2022 - 08 - 18 T 06: 15 Z; eventTime: 05: 41 Z / 06: 15 Z; year: 2022; month: 8; day: 18; habitat: hadal sediment; fieldNumber: AB 3572 | MOL- 0570; Record Level: language: en; institutionCode: SMF; basisOfRecord: PreservedSpecimen

Description

Animal relatively large for the genus (5.2 mm long, 4.0 mm wide, 2.0 mm high), width to length ratio 0.77, height to length ratio 0.38 (Fig. 14 A – C). Shell fragile, pale, translucent, whitish. Aperture ovoid, evenly rounded posteriorly, slightly narrowing anteriorly. Apex protruding beyond anterior shell margin, but forming a regularly curved arc with dorsal teleoconch surface in lateral view. Apical cap approximately 280 μm long, 250 μm wide, positioned at an angle of slightly more than 100 ° relative to the ventral plane, eroded in the holotype, smooth except for six closely-spaced concentric ridges at transition to teleoconch (Fig. 14 F, arrowheads). Shell surface ornamented with prominent reticulate sculpture comprised of numerous concentric ribs with irregular interspacing, but becoming slightly closer together distally. Radial ribs slightly thinner and less prominent than the concentric sculpture, spaced more closely at posterior, with broader interspacing at anterior. Rib intersections with weak nodes (Fig. 14 E, G), delimiting rectangular interspaces of variable size.

Foot prominent, subcircular, surrounded by a wide, shallow pallial groove; five digitate gills per side, each approximately as long as the width of the pallial groove in the preserved specimen. Anterior velar lobes large, elongated, leaf-like, almost three times as long as the diameter of the anterior lip. Postoral tentacles well-developed. Radula docoglossan with one pair of prominent major teeth (visible in micro-CT; Fig. 14 D); radula cartilages large. Eight dorso-ventral muscles per side, first pair (counting from anterior) immediately posterior to radula cartilages; second pair divided into two distinct bundles of inequal size (anterior part smaller). Gut with six loops.

Type material

Holotype (SMF 373808).

Material examined

Only known from the holotype.

Type locality

Northeast Pacific Ocean, Aleutian Trench, south of Unalaska Island, 51°55.94'N, 166°51.84'W to 51°55.94'N, 166°51.85'W, 6465 m depth.

Diagnosis

Large-sized Veleropilina (shell length> 5 mm); shell moderately elevated (height to length ratio 0.38), surface covered by prominent reticulate sculpture with almost equally thick radial and concentric ribs delimiting rectangular to squarish interspaces. Aperture ovoid, narrowing anteriorly. Apex protruding beyond anterior shell margin, forming a regularly curved arc with the dorsal teleoconch surface when viewed laterally. Apical cap large, approximately 280 μm long and 250 μm wide, positioned at an angle of slightly more than 100 ° relative to the ventral plane. Postoral tentacles and velar lobes well-developed, the latter more than three times longer than the diameter of the anterior lip. COI mitochondrial barcode region with 12.71 % difference (87.29 % BLAST similarity) to that recovered from the V. oligotropha (s. l.) genome of Chen et al. (2025) and 7.23 % difference (92.77 % similarity) to another previously published COI sequence of V. oligotropha (NCBI accession MF 157522, Wiklund et al. (2017)) in a smaller region of sequence overlap.

Etymology

Named after Dr Gretchen Van Meer Sigwart, civil engineer and professor, in recognition for her pioneering accomplishments and advocacy for equality and support for women in science, LGBTQ rights and people with disabilities.

Distribution

Only known from the type locality.

Taxon discussion

The new species differs from other congeners in several respects. Previously published analyses of the genome of Veleropilina gretchenae sp. nov. (sequenced from the holotype, as Veleropilina sp.) and a specimen identified as V. oligotropha (Rokop, 1972) revealed significant differences with an estimated divergence time of 72 million years (Chen et al. 2025). This substantial separation sheds new light on the importance of apparently minor morphological differences. Amongst these, the most obvious are body size, apertural shape and lateral shell profile: V. gretchenae sp. nov. is considerably larger than V. oligotropha and has an aperture that narrows anteriorly; its apical cap is well-aligned with the dorsal teleconch surface located behind it, forming a smooth, regularly curved arc, whereas it represents a prominent, growth stage-independent discontinuity or bump in V. oligotropha. In size, proportions of the shell and dimensions of the apical cap, V. gretchenae sp. nov. is most similar to V. zografi (Dautzenberg & H. Fischer, 1896) from the North Atlantic Ocean, but differs in the sculpture (relatively broad and low-profile, very narrowly-spaced concentric ribs in V. zografi) as well as geography (Warén and Gofas 1996). The radula of V. gretchenae sp. nov. as visible in micro-CT appears to be structurally similar to Veleropilina seisuimaruae Kano et al., 2012, although this is not entirely clear from the available data; as the holotype of the former species was badly damaged due to tissue sampling for genomic analysis, we elected not to pursue further dissection. All previously described species in Veleropilina, except V. oligotropha, occur at much shallower depths (Kano et al. 2012). Veleropilina gretchenae sp. nov. can most usefully be compared to other species in the genus reported from the Pacific (Table 3), highlighting the distinctive characters of V. gretchenae sp. nov.: larger size, relatively tall shell and large apical cap.

Methods

The holotype of V. gretchenae sp. nov. was collected during the SO 293 AleutBio expedition of German R / V SONNE in 2022, using a 3.5 m-wide Agassiz trawl with 10 mm cod end mesh size (OKTOPUS GmbH). Contents of the net were sieved on a 1 mm mesh and subsequently preserved in 96 % ethanol (Brandt 2022).

Photographs of the intact specimen were taken on board, prior to tissue sampling for genome sequencing (methods described in Chen et al. (2025), Electronic Supplementary Materials).

To molecularly compare the new species with the morphologically similar congener V. oligotropha (Rokop, 1972), both species’ COI sequences were extracted from published genomic datasets (Chen et al. (2025), with V. gretchenae sp. nov. reported as V. sp.); a further COI sequence of V. oligotropha from the Clarion-Clipperton Zone was downloaded from GenBank (accession no. MF 157522; Wiklund et al. (2017)). Sequence similarity between V. gretchenae sp. nov. was assessed using NCBI BLAST (Camacho et al. 2009). The COI sequence isolated from the genome of V. gretchenae sp. nov. for the purpose of this study was uploaded to the Barcode of Life Data Systems (BOLD) (see Materials section for details).

Shell microsculpture and apical cap morphology was investigated and documented, based on shell fragments (produced by invasive tissue sampling) after air drying them, using a HITACHI TM 4000 Plus Tabletop scanning electron microscope (SEM) without metal coating.

Soft body anatomy was studied from a micro-computed tomography (micro-CT or µCT) scan performed at the ANATOMIX beamline, synchrotron SOLEIL, Paris, following the methods and settings described in Ampuero and Sigwart (in press). Prior to CT scanning, the specimen was incubated in a contrasting solution of 0.3 % phosphotungstic acid and 3 % dimethyl sulphoxide in 95 % ethanol (Senckenberg Ocean Species Alliance (SOSA) et al. 2024) for ca. 1 week. The x-ray virtual section shown was produced with Dragonfly software (v. 2022.2; OBJECT RESEARCH SYSTEMS).

Shell measurements (length, width, height) were taken from habitus images of the intact specimen using NIKON NIS Elements Basic Research software (v. 5.42. 04). Apical cap size was determined from SEM images using TM 4000 software (HITACHI Ltd, Tokyo, Japan).

Image processing and figure plate assembly was performed in Adobe Photoshop 2025.

Specimen data for this description were gathered and processed via the Discovery Laboratory of the SENCKENBERG OCEAN SPECIES ALLIANCE.

Repository: The holotype is housed at the Senckenberg Research Institute and Natural History Museum Frankfurt (SMF).