Shinkailepas cornuthauma, Gu & Chen & Gao & Zhou & Sun, 2025

Gu, Xinyu, Chen, Chong, Gao, Kexin, Zhou, Yadong & Sun, Jin, 2025, Integrative taxonomy of new neritimorph limpets from Indian Ocean deep-sea hot vents shed light on their biogeographic history, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 203 (1), pp. 1-15 : 8-12

Shinkailepas cornuthauma sp. nov.

( Figs 5–7 )

Shinkailepas sp. Zhou et al. (2022): supplementary table S5 (at least the sequenced individual from the Daxi field belongs to this species).

ZooBank registration: urn:lsid:zoobank.org:act:BD73673D-FE2F-449C-82CE-DA2F6A4B989D

Diagnosis: Medium-sized Shinkailepas (SL ≤ 12 mm) with the apex weakly inclined to the right and positioned at approximately 70% from the anterior shell edge. Shell sculpture weakly cancellate with radial ribs much stronger than concentric ribs, raised nodes are formed where the two directions meet. Septum (‘deck’) reduced and minute. Epipodial fold carries 15–18 small triangular tentacles. Operculum entirely corneous. Diameter of opercular nucleus approximately 500 μm.

Type locality: Daxi hydrothermal vent field, Carlsberg Ridge.

Type material: Holotype ( RSIO 38227 ; Figs 5B , 6–7 ), male, 95% ethanol, SL 11.7 mm, SW 8.4 mm, male; Daxi vent field, Carlsberg Ridge, 60°10.8 ʹ E, 6°48.0 ʹ N, 3480 m deep, R/V Xiangyanghong 9 cruise DY38, collected by a seven-function manipulator of HOV Jiaolong on dive 126, March 2017 . Paratype 1 ( RSIO 38228 ; Fig. 5C ), female, 95% ethanol, shell broken during collection, animal approximately 8.5 mm in length and 5.5 mm in width, same collecting data as holotype .

Material examined: One specimen ( RSIO 38229 ; Fig. 5 A ), female, 95% ethanol, SL 6.7 mm, SW 5.0 mm, Wocan vent field (60°31.8 ʹ E, 6°21.6 ʹ N), 2920 m deep, collected by a seven-function manipulator of HOV Jiaolong on dive #125, R/V Xiangyanghong 9 cruise DY38, March 2017 .

Description: Shell ( Fig. 5 ) medium-sized for genus, adult limpet-formed, with evidence of coiling when juvenile. Shell length 1.2–1.4 times of width; shell height approximately onequarter of length. Aperture oval, reduced and minute septum (‘deck’) present posteriorly. Apex positioned at approximately 30% from posterior shell edge, weakly recurved to right side. Shell sculpture dominated by very strong radial ribs crossing with concentric growth lines to form weakly cancellate sculpture; raised protuberances form where two directions converge. Radial sculpture with three to five minor ribs between each pair of major ribs. Shell margin rather flat. Shell interior translucent-white, with numerous shell pores. Ostracum moderately thin, translucent. Numerous shell pores present on inner ostracum surface but absent on septum. Shell microstructure ( Fig. 7A ) with three layers dorsal to the myostracum, a thin outermost granular layer, followed by a thick simple prismatic layer, then by an equally thick crossed lamellar layer. Protoconch unknown as corroded in all specimens available for study. Periostracum moderately thick, greenish, often covered in rusty mineral deposits.

External anatomy ( Fig. 6A–C ) typical for genus, most characters agree well with those described under S. tiarasimia above. Epipodial fold ( Fig. 5 ) carries 15–18 small triangular tentacles posteriorly. Operculum ( Fig. 6D ) large, entirely corneous, occupying over half of dorsal surface of foot, exact shape could not be determined due to its folded condition in examined specimens from preservation issues. Diameter of opercular nucleus approximately 500 μm, but due to its folded state, exact measurement was not possible.

Radula ( Fig. 7B–D ) rhipidoglossate, overall dentition pattern typical for genus ( Fukumori et al. 2019), formula c. 100–4–1–4– c. 100. Central tooth subquadrate, about 1.5 times as long as wide, with thickened central ridge running horizontally. Innermost first lateral film-like, strongly oblique, twice as wide as central tooth, cusp indistinct, lacking serration, curled over distally to form overhanging flap, outermost side with raised fold. Second lateral narrower than central tooth, hook-shaped with shaft recurved inwards, inner side of shaft with one raised hump; double-cusped with upper one smooth, lower one carrying four sharp minor cusps. Third lateral ( Fig.7D ) narrow with inward-rolled shaft, with one minute denticle, otherwise smooth. Outermost fourth lateral large, with solid, smooth, very slightly inwardly recurved shaft, distally enlarging to form wide cusp divided into five denticles, of which second from inside strongest by far. Inner marginals with shafts similar in length to fourth lateral, serrated into 4–5 denticles distally. Outer marginals much smaller, cusp rake-like, serrated into many fine denticles whose numbers increase outwards.

Etymology: The specific epithet is a combination of Latin cornū (‘horn’) and Ancient Greek thaûma (‘wonder, marvel, astonishment’), referring to its horn-like, curved apex and the wonderful happening of collecting the few specimens known, allowing its formal description. This name was also partly inspired by the magical helm ‘ cornuthaum ’ that appears in the roguelike video game NetHack. Used as noun in apposition.

Distribution: Only known from the Daxi and Wocan vent fields on the CR.

Remarks: Shinkailepas cornuthauma is clearly distinct from other described Shinkailepas species by its relatively anterior apex position at approximately 30% of SL from the posterior shell edge, a very reduced septum (‘deck’), combined with its strong radial shell sculpture with three to five minor ribs between two major ribs. Shinkailepas tollmanni is the only similar species with a similarly reduced condition of the septum, but its sculpture consists solely of fine radial ribs which are smooth instead of strongly granulated as in S. cornuthauma ( Beck 1992, Fukumori et al. 2019). Furthermore, the epipodial tentacles of cornuthauma are small, triangular, and number between 15–18, which aids to distinguish it from species like S. conspira and S. gigas whose epipodial folds are divided into over 50 large, paddle-like projections ( Chen and Sigwart 2023, Senckenberg Ocean Species Alliance et al. 2024).

Molecular analyses

Our phylogenetic tree reconstructed using the COI gene ( Fig. 8 ) recovered a strongly supported monophyletic genus Shinkailepas (Bayesian Posterior Probability, BPP = 0.9) including S. tiarasimia and S. cornuthauma , supporting their inclusion in this genus. Two major clades were recovered within Shinkailepas , one containing S. kaikatensis , S. gigas , and S. cornuthauma (‘Clade A’ hereafter) and the other with all remaining species (‘Clade B’ hereafter); both were strongly supported (BPP = 0.94 and 0.96, respectively). Within Clade A, S. cornuthauma was the earliest diverging species sister to the S. kaikatensis — S. gigas pair, but only with low support (BPP <70). Within Clade B, there was a basal split between the fully supported (BPP = 1) Shinkailepas aff. tufari Woodlark Basin and Shinkailepas sp. Mariana Trough (sensu Poitrimol et al. 2022) pair and all other taxa. Shinkailepas tiarasimia was recovered as sister to S. conspira with strong support (BPP = 0.98). This pair was in turn clustered with S. aff. tufari Lau Basin & Futuna Arc ( Poitrimol et al. 2022) with moderate support (BPP = 0.84). These three taxa were weakly supported (BPP <0.70) as sister to the S. myojinensis and S. tollmanni pair. Shinkailepas tufari was found to be the closest relative of these five species, with moderate support (BPP = 0.83).

From estimates of genetic divergence between Shinkailepas species using the COI gene (Table 1), the K2P distance between S. tiarasimia and other known congeners ranges from 6.65 to 8.86% and the same for S. cornuthauma ranges from 7.05 to 11.75%. This is roughly equivalent to the range observed among other Shinkailepas species (5.50–11.42%), and above the lowest value of 5.50% between two described species ( S. tollmanni — S. tufari ). These support the recognition of S. tiarasimia and S. cornuthauma as new species of Shinkailepas .

Figures

Figure 5. Shinkailepas cornuthauma, specimens examined in this study. A, specimen collected from Wocan field (RSIO 38229), female. B, holotype (RSIO 38227), male. White arrow indicates the penis. C, paratype 1 (RSIO 38228), female, shell damaged during collection.

Figure 6. Shinkailepas cornuthauma, external anatomy of the holotype male (RSIO 38227). A, dorsal aspect with shell removed.B, enlarged dorsal view of the head with mantle edge removed, female. C, enlarged ventral of the head.D, operculum shown attached to dorsal aspect of foot.Abbreviations:ang, annex gland; cl, cephalic lappet; ct, ctenidium; dg, digestive gland; e, eye; f, foot; lsm, left shell muscle; m, mouth; me, mantle edge; nl, neck lobe; ol, oral lappet; pe, penis; pc, pericardium; pr, prostate; rsm, right shell muscle; sn, snout; st, stomach; t, cephalic tentacle; te, testis.

Figure 7. Shinkailepas cornuthauma, scanning electron micrographs of the holotype (RSIO 38227). A, shell microstructure. B, overview of the radula. C, close-up of the left half of the radula. D, close-up of the outer laterals and marginal teeth.

Figure 8. Phylogenetic tree of Shinkailepas reconstructed using Bayesian inference from 658 bp of the mitochondrial cytochrome c oxidase subunit I (COI) gene.GenBank accession numbers of the sequences included are shown in parentheses. Node values indicate Bayesian posterior probabilities, only those higher than 0.7 are shown. Representation of undescribed species follows Poitrimol et al.(2022); Woodlark, Lau, and Futuna refer to Woodlark Basin, Lau Basin, and Futuna Arc in the southwestern Pacific, respectively.