Neolepetopsis prismatica Chen & Zhou & Watanabe & Zhang & Wang 2022, SP. NOV.
Creators: name: Chen, Chong
name: Zhou, Yadong
name: Watanabe, Hiromi Kayama
name: Zhang, Ruiyan
name: Wang, Chunsheng
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Patellogastropoda
Neolepetopsidae
Neolepetopsis
Neolepetopsis prismatica

description: NEOLEPETOPSIS PRISMATICA SP. NOV.
(FIGS 2A–D, 3, 4)
Z o o B a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. org:act: B0DF7474-BE16-461E-B07E-632D276D0E66
Diagnosis: Medium-sized Neolepetopsis (SL ≤ 4.8 mm) with much stronger concentric sculpture compared with only diminutive, nearly absent radial sculptures and lacking nodes at the intersecting points. Spacing of concentric sculptures variable between ~50 and 150 µm within the same individual. Shell oval; posterior end narrower than anterior; always low profile and flat limpet-form, with apex on the midline and nearly central or very slightly anterior. Symmetrical protoconch 220 µm in length. Greenish periostracum present. Interior of the semi-transparent shell carrying strong prismatic structural colour. Radula with short shafts and heavy, well-mineralized cusps.
Type locality: Inactive sulfide deposits, Daxi hydrothermal vent field, Carlsberg Ridge.
Type material: Holotype (RSIO 38210; Fig. 2A) in 95% ethanol, SL 4.1 mm, SW 3.1 mm, Daxi vent field, Carlsberg Ridge, 60°10.8′E, 6°48.0′N, 3450 m deep (station ‘DV128’), R / V Xiangyanghong 9 cruise DY38, by a seven-function manipulator of HOV Jiaolong, dive 128, 11 March 2017. Paratype 1 (NSMT-Mo 79214; Figs 2B, 3), 95% ethanol, SL 4.2 mm, SW 2.9 mm, rehydrated once for photography of soft parts and then stored in 70% ethanol. Paratype 2 (RSIO 38211; Fig. 2C), 95% ethanol, SL 4.0 mm, SW 2.8 mm. Paratype 3 (NSMT-Mo 79215; Fig. 2D), 95% ethanol, SL 3.5 mm, SW 2.4 mm. Paratype 4 (NSMT-Mo 79216), 95% ethanol, SL 4.1 mm, SW 2.9 mm. Paratype 5 (NSMT-Mo 79217), 95% ethanol, SL 3.9 mm, SW 2.8 mm. Paratype 6 (RSIO 38212), 95% ethanol, SL 4.8 mm, SW 3.3 mm. Paratype 7 (NSMT-Mo 79218), 95% ethanol, five small specimens. Paratype 8 (RSIO 38213), 95% ethanol, five small specimens. Paratype 9 (RSIO 38214), 95% ethanol, shell only, SL 4.8 mm, SW 3.1 mm. All paratypes are from the same lot as the holotype.
Description: Shell(Fig.2A–D)thin, mostlytransparent, carrying strong prismatic structural coloration on internal surface. Shell length ≤ 4.8 mm, shell width ≤ 3.3 mm (4.1 and 3.1 mm for holotype, respectively). Small area corresponding to apex thickest, slightly opaque, thinning out towards periphery. Elliptic to oval in shape, with posterior end slightly narrower than anterior end; shell length-to-width ratio between 1.3:1 and 1.5:1. Always low in profile, with nearly flat shell edge. Apex at midline, nearly central or slightly anterior. Sculpture predominantly concentric (Figs 2, 3C), with strong concentric ribs at somewhat variable interspaces between ~50 and 150 µm, even within each individual. Radial sculpture almost lacking, with only weak radial striations. No nodes formed at intersection between two directions of sculptures. Protoconch (Fig. 3A, B) symmetrical, typical of patellogastropods, 220 µm in length. Finely pitted sculpture present on protoconch, especially obvious at distal end. Thin, greenish layer of periostracum present over teleoconch. Muscle scars not clearly discernible.
Radula (Fig. 3D, E) with seven mineralized teeth (rachidian, two pairs of laterals, pluricuspid) on each row and four non-mineralized marginal teeth, width ~25 µm. Cusps of mineralized teeth gradually descending in horizontal position from rachidian outwards. Rachidian sturdy; base laterally expanded with narrow, short shaft ending in a single tapering, overhanging cusp. Inner lateral also with overhanging, but narrower, cusp stemming from narrow shaft possessing strong indentation to accommodate expanding base of rachidian. Outer pair of laterals similar to inner pair but sturdier, with much thicker shaft and with heavier, triangular cusp. Pluricuspid tooth with broad cusp bearing three tapering tips, the two outer ones being much larger. Shaft of pluricuspid with broad basal–lateral indentation, extension of which connects with inner marginal tooth. Inner marginal with broad, overhanging edge, on strongly indented, broad shaft. Outer marginal separated from inner marginal, much reduced, with narrow, tapered, overhanging edge.
The soft parts are shown in Figure 4. Cephalic tentacles simple, tapering; left and right tentacles of equal size. External evidence for eyes absent. Mouth with thick outer lip; labial lobe well developed. Jaw present. Foot oval, with unciliated rim. Large sole demarcated from rim by deep groove. Epipodium lacking. Shell muscle U-shaped, situated along posterior two-thirds of body, separated into several oval-shaped bundles decreasing in size from anterior towards posterior end. Mantle edge with numerous short, presumably sensory papillae; fully contracted in specimens examined. Mantle cavity approximately one-third of body length. Pericardium situated on left side of mantle roof, heart monotocardian, with anterior auricle and posterior ventricle (by transparency). Right side of mantle roof with anus just left of the urogenital opening situated on sizeable papillae. Ctenidium lacking. Sexes separate; gonad located above foot at mid-ventral position, visible from dorsal view by transparency posterior to pericardium. Two kidneys present; left kidney minute compared with sizeable right kidney at far posterior. Intestine and stomach embedded in large digestive gland comprising numerous branching tube-like structures. After two loops, intestine transitions to rectum, running posterior–anteriorly before curving to right, with anus exiting at right side of mantle roof. Rectum packed with dark oval faecal pellets. Operculum lacking.
Etymology: From the Latin adjective prismaticum meaning ‘prismatic’, originally derived from Ancient Greek Πρίσµα, prísma, something sawn. It is named in reference to the brilliant iridescence of its shell, particularly the inner surface, owing to structural colour.
Distribution: Currently known only from inactive sulfide chimneys of the Daxi hydrothermal vent field on the Carlsberg Ridge, Indian Ocean. The Daxi field has a central focused venting area surrounded by a region characterized by numerous extinct sulfide chimneys (Wang et al., 2021), on which the present new species was collected.
Remarks: Five other described species are currently known in Neolepetopsis, all from the eastern Pacific Ocean. The shell sculpture of N. prismatica differs from these species in lacking clear nodes where the concentric ribs meet the radial ones, owing to radial sculpture being extremely weak. The protoconch of N. prismatica is much smaller than that of Neolepetopsis densata McLean, 1990 from East Pacific Rise vents (McLean, 1990), the only other Neolepetopsis species with a known protoconch (220 vs. 400 µm). The radula of N. prismatica is also most similar to N. densata, with shorter shafts and more prominent cusps than N. gordensis from vents on the East Pacific Rise (McLean, 1990) and also recorded at hydrocarbon seeps off Peru (although whether this record truly represents N. gordensis remains uncertain; Warén & Bouchet, 2001). The radula of other Neolepetopsis species (where known) has either two (N. gordensis) or four (N. densata) cusps on the pluricuspid (McLean, 1990), whereas that of N. prismatica has three. The short shafts of the N. prismatica radula are similar to N. densata but unlike the longer shafts of N. gordensis. The radula of Neolepetopsis nicolasensis McLean, 2008 from a whale fall off California is unique in having only five cusped teeth instead of seven (McLean, 2008) and therefore cannot be confused with the present new species. The flat shell with green periostracum and stronger concentric sculpture is also seen in Neolepetopsis verruca McLean, 1990 and Neolepetopsis occulta McLean, 1990 from vents on the East Pacific Rise (McLean, 1990), but the radial striation on N. prismatica is far weaker than in either of these two species, both also exhibiting nodes where the two sculpture types meet. For differences from Neolepetopsis ardua, see below under that species.
description: Published as part of Chen, Chong, Zhou, Yadong, Watanabe, Hiromi Kayama, Zhang, Ruiyan & Wang, Chunsheng, 2022, Neolepetopsid true limpets (Gastropoda: Patellogastropoda) from Indian Ocean hot vents shed light on relationships among genera, pp. 276-296 in Zoological Journal of the Linnean Society 194 on pages 280-282, DOI: 10.1093/zoolinnean/zlab081, http://zenodo.org/record/5799980