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

Shinkailepas tiarasimia sp. nov.

( Figs 2–4 View Figure 2 View Figure 3 View Figure 4 )

Shinkailepas Van Dover et al. (2001): 821 View in CoL , table 2.

Shinkailepas sp. Watanabe and Beedessee (2015): 16, table 16.1. Shinkailepas sp. CIR (Central Indian Ridge) Kim et al. (2020): supplementary table S1.

‘ Lepetodrilidae View in CoL fam. inc.’ Gerdes et al. (2021): 219, fig. 201, table 3.

ZooBank registration: urn:lsid:zoobank.org:act:8B81A710-BFCB-4F5E-A588-1A1CA44949F2

Diagnosis: Medium-sized Shinkailepas (SL ≤ 8.5 mm) with apex slightly bent to left, positioned near posterior shell margin at about 90% from anterior edge. Shell sculpture cancellate with concentric sculpture equal in strength or stronger than radial ones, drawn out to form weak nodes where they cross. Protoconch bulbous, smooth except for micro-pustules, about 660 μm in size when measured from adult shell. Diameter of opercular nucleus (see Fukumori and Kano 2014) 475 μm. Ostracum translucent, with silvery sheen. Operculum entirely corneous, not calcified. Epipodial fold with 12–15 short, triangular, tentacular projections.

Type locality: Wocan hydrothermal vent field, Carlsberg Ridge.

Type material: Holotype ( RSIO 38219 ; Fig. 2A View Figure 2 ), female, 95% ethanol; SL 5.3 mm, SW 4.2 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 #129, R/V Xiangyanghong 9 cruise DY38, March 2017 GoogleMaps . Paratype 1 ( RSIO 38220 ; Figs 2B View Figure 2 , 3D View Figure 3 ), female, 95% ethanol; SL 6.5 mm, SW 5.4 mm GoogleMaps . Paratype 2 (RSIO 38221; Figs 2C View Figure 2 , 3C View Figure 3 ), female, 95% ethanol; SL 4.5 mm, SW 3.6 mm GoogleMaps . Paratype 3 ( RSIO 38222 ; Fig. 3B View Figure 3 ), female, 95% ethanol, radula dissected for SEM ( Fig. 4E–F View Figure 4 ); SL 4.1 mm, SW 3.1 mm GoogleMaps . Paratype 4 ( RSIO 38223 ; Fig. 2D View Figure 2 ), male, 95% ethanol; SL 3.7 mm, SW 2.9 mm GoogleMaps . Paratype 5 ( RSIO 38224 ; Fig. 4C–D View Figure 4 ), male, 95% ethanol, periostracum removed for SEM; SL 5.9 mm, SW 3.9 mm GoogleMaps . Paratype 6 ( RSIO 38225 ; Fig. 4C–D View Figure 4 ), female, 95% ethanol ( Fig. 3A View Figure 3 ); SL 4.8 mm, SW 3.7 mm. All paratypes with same collecting data as holotype GoogleMaps .

Material examined: One shell (NSMT-Mo 79568; Fig. 4A–B View Figure 4 ), periostracum of the protoconch removed for SEM, 99% ethanol; SL 8.4 mm, SW 6.1 mm; Kairei vent field (70°2.4187 ʹ E, 25°19.2315 ʹ S), 2424 m deep, collected by suction sampler mounted on HOV Shinkai 6500 on dive #1449, R / V Yokosuka cruise YK16-E02, Feb 13 2016. Lot of five specimens ( RSIO 38226 ), 95% ethanol, up to SL 5.1 mm, SW 3.9 mm; Wocan vent field (60°31.8 ʹ E, 6°21.6 ʹ N), 2970 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. 2 View Figure 2 ) medium-sized for genus, nearly limpet-form as adults but conspicuously coiled at juvenile stage. Aperture oval, 1.1–1.3 times as long as wide. Height about one-third of length. Apex overhanging, close to shell edge at approximately 10% of length from posterior margin, recurved slightly to left side. Shell sculpture cancellate from crossing of concentric sculpture with radials, forming low protrusions where two directions meet. Concentric sculptures stronger than or equal in strength to radials. Shell margin nearly flat to slightly raised ( Fig. 2A–B View Figure 2 ). Septum (‘deck’) large, conspicuous, occupying anterior one-fourth of aperture at posterior ( Fig. 2B, E View Figure 2 ). Inner shell surface carry numerous shell pores, absent on septum. Ostracum thin, translucent-white with silvery sheen. Shell microstructure ( Fig. 4C View Figure 4 ) of three layers dorsal to myostracum, outermost homogeneous layer thin, followed by another thin granular layer, innermost crossed-lamellar layer thick. Periostracum thin, translucent, light to bright green ( Fig. 2 View Figure 2 A-D), typically with some sulphide mineral deposits on top ( Fig. 3D View Figure 3 ), in extreme cases shell may appear to become reddish in appearance due to rusty deposits, as known for some other Shinkailepas species ( Fukumori et al. 2019). Protoconch ( Figs 2F View Figure 2 , 4A View Figure 4 ) white, covered by dark purple-red periostracum, bulbous, approximately 660 μm in length when measuring exposed part from adult shells, completely smooth except for minute dimples of 1–2 μm in size ( Fig. 4B View Figure 4 ).

External anatomy ( Figs 2C–D View Figure 2 , 3A–C View Figure 3 ) typical for genus ( Sasaki et al. 2006). Cephalic tentacles simple conical, tapered, elongate. Cephalic lappets small, positioned immediately anterior of cephalic tentacle. Left cephalic lappet develops into conical penis ( Fig. 2D View Figure 2 ) in males. Triangular neck lobe present posterior of cephalic tentacles. Eyes present, with dark pigments. Oral disc ( Fig. 2C–D View Figure 2 ) circular with strongly muscular outer lip, surrounded by well-developed oral lappet as wide as oral disc to either side. Dorsal surface ( Fig. 3A View Figure 3 ) covered by thin mantle with thickened edge lacking major tentacles. Hypobranchial gland lacking. Shell muscle divided into two, left shell muscle reaching slightly anterior of right shell muscle. Pallial edge slightly anterior of left shell muscle edge. Single ctenidium bipectinate, oblique in position with base at posterior left extending to anterior right. Intestine visible on dorsal mantle wall immediately posterior of ctenidium. Pallial gonoduct attached on dorsal mantle ceiling, surrounded anteriorly by capsule gland and posteriorly by albumen gland in females; in males replaced by prostate anteriorly and annex gland posteriorly. Pericardium triangular, on posterior left just posterior or ctenidium. Part of stomach visible on most posterior part of dorsal visceral mass, surrounded by extensive digestive gland dorsal to extensively developed gonad. Foot ( Fig. 2C View Figure 2 ) with circular, flattened sole, anterior pedal gland present. Epipodial fold carries 12–15 short, triangular tentacles. Operculum ( Fig. 3C View Figure 3 ) present, attached to dorsal surface of foot below visceral mass, thin, translucent, rather symmetrical in outline but with thickened nucleus area at left side, entirely corneous with no evidence of calcification. Diameter of opercular nucleus (see Fukumori and Kano 2014) 475 μm.

Radula ( Fig. 4E–F View Figure 4 ) rhipidoglossate, formula c. 80–4–1– 4– c. 80. Central tooth oblong-quadrate, twice as long as wide, dorsal surface smooth, distally with very weak anterior ridge, overhanging cusp lacking. Innermost first lateral large, film-like, obliquely positioned with outer edge much higher than central tooth. Anterior edge of first lateral rolled to form weakly overhanging, smooth cusp; outermost edge raised to form vertical ridge. Second lateral small with inwardly recurved shaft, positionally occupying anterior half of first lateral, distally equipped with double overhanging cusps. Anterior cusp of second lateral smooth, posterior cusp with five to six denticles. Third lateral with strongly rolled shaft enveloping second lateral, cusp oblique with single major denticle whose inner side carries irregular serration. Outermost fourth lateral large, 1.5 times as long as third lateral, with slightly inwardly recurved shaft that gradually expands distally to form large, overhanging cusp with one inner, major denticle plus three outer, minor denticles. Inner marginals ( Fig. 4F View Figure 4 ) as long as fourth lateral, distally serrated into rake-like cusp with five to six denticles. Outer marginals much longer than inner marginals with elongate shafts ending in very finely serrated cusps, increasingly so outwards.

Egg capsule ( Fig. 3D View Figure 3 ) about 0.6 mm in size, oblong oval, semi-transparent, similar in shape to other Shinkailepas egg capsules previously illustrated in literature ( Metaxas 2011). Only one found on shell surface (of paratype 1; Fig. 2B View Figure 2 ), at least seven embryos can be seen inside the capsule.

Etymology: Greek, tiára (‘headdress’) + asimía (‘silvercoloured’), feminine adjective. Refers to the silver sheen of the ostracum and its cap-like shape, reminiscent of oriental silver headdresses.

Distribution: Known with certainty from hydrothermal vents on both the CR (Wocan field) and the CIR (Kairei field).

Remarks:

Morphologically S. tiarasimia most closely resembles S. conspira from the Lau Basin in the southwestern Pacific ( Poitrimol et al. 2022, Chen and Sigwart 2023), which exhibits similar shell sculpture with concentric ribs stronger than radial ones equal in strength, a similar apex position near the shell posterior, as well as a similar radula morphology. These two species, however, can be clearly differentiated in that the epipodial lobe of S. conspira is well developed and bears up to 60 paddle-like flaps ( Chen and Sigwart 2023) compared to S. tiarasimia where only 12–15 small triangular tentacles are present. Shinkailepas conspira is also notably a much larger species reaching up to 21.3 mm in SL ( Chen and Sigwart 2023). Another species sharing a similar adult shell sculpture is S. tufari from the Manus Basin vents also in the southwestern Pacific ( Poitrimol et al. 2022); however, S. tufari has a much larger septum positioned at approximately the midpoint of the aperture ( Beck 1992).

While S. myojinensis typically exhibits stronger shell sculpture than S. tiarasimia ( Sasaki et al. 2003) this species can be morphologically very variable and some specimens may resemble S. tiarasimia ( Yahagi et al. 2017) , but the operculum of S. myojinensis is partly calcified (likewise in S. conspira and S. tufari ), whereas in S. tiarasimia it is entirely corneous. The protoconch of both S. conspira and S. tufari are both about 800 μm in size ( Beck 1992, Chen and Sigwart 2023), much larger than the 660 μm in S. tiarasimia ; while that of S. myojinensis is similar and also 660 μm ( Sasaki et al. 2003). However, we note that our protoconch size is measured from the exposed part in adult shells unlike those of S. myojinensis and S. tufari which are measured using juveniles ( Beck 1992, Sasaki et al. 2003). As the teleoconch of Shinkailepas often envelops the protoconch during growth, our measurement of the protoconch size is likely less accurate than those measured from juveniles. The central teeth of S. tiarasimia also appear to lack a horizontal ridge that is prominent in S. myojinensis ( Sasaki et al., 2003) .