Anatoma paucisculpta, Hoffman & Kniesz & Arbizu & Kihara, 2022

Hoffman, Leon, Kniesz, Katharina, Arbizu, Pedro Martínez & Kihara, Terue C., 2022, Abyssal vent field habitats along plate margins in the Central Indian Ocean yield new species in the genus Anatoma (Vetigastropoda: Anatomidae), European Journal of Taxonomy 826, pp. 135-162 : 155-157

Anatoma paucisculpta sp. nov.

urn:lsid:zoobank.org:act:337D20DA-8BE8-4C69-82A1-8EE444B72C48

Fig. 11

Etymology

The species name ‘ paucisculpta ’ refers to the inconspicuous sculpture on the shell.

Type material

Holotype INDIAN OCEAN • CIR; 23.88° S, 69.62° E; depth 3296 m; 8 Dec. 2015; stn INDEX15_62R; spec. I15 _Ma_169, SEM, Fig. 11D–H ; SMF 358992 .

Paratypes INDIAN OCEAN • 1 juvenile shell; SEIR; 27.63° S, 73.87° E; depth 2618 m; 6 Dec. 2019; stn INDEX19_104RO; spec. I19 _Ma_91, SEM, Fig. 11A–C ; SMF 358993 .

Other material examined

INDIAN OCEAN • 2 specimens; SEIR; 27.63° S, 73.87° E; depth 2532–2621 m; 7 Dec. 2019; stn INDEX19_106RO; specs I19 _Ma_ 52, I19 _Ma_71 • 2 specimens; SEIR; 27.65° S, 73.88° E; depth 2469 m; 23 Nov. 2018; stn INDEX18_063RO; specs I18 _Ma_271–272 .

Shell description

PROTOCONCH ( Fig. 11F ). One slightly elevated whorl, evenly rounded, sculpture small, irregularly oriented, straight or curved, short ridges; few spiral striae; smooth straight rim near margin; sharp flexuous lip, protrusion at periphery; transition to teleoconch clear by change in sculpture; diameter 0.21 mm.

TELEOCONCH ( Fig. 11D–E ). With elevated spire, swollen whorls with protruding margins of selenizone; with spiral cordlets; rounded aperture with slit; suture deep. Height 1.0 mm, width 1.2 mm, height of aperture 0.7 mm (70 % of total height); colour translucent grayish white. 2¼ regular whorls with convex shoulder area and rounded base, selenizone slightly above periphery. Teleoconch I from protoconch to start of selenizone: slightly more than one well-rounded whorl, descending below protoconch; smooth, with up to six spiral cordlets, numerous prosocline growth lines. Teleoconch II with selenizone: slightly more than one whorl; shoulder area with seven spiral cordlets at the lip margin; new weaker cordlets emerging between older ones. Margins of selenizone sharply protruding outwards; growth lines on external sides of selenizone; inside margins smooth; surface between margins smooth with curved growth lines ( Fig. 11B, E, H ). Base body whorl smooth background with about 20 irregularly spaced

spiral cordlets and about 60 regular axial riblets; spiral and axial sculpture stronger in umbilical area ( Fig. 11G ).

UMBILICUS. Open, tortuous and deep; steep smoothly curved spiral keel ending at base of columellar callus ( Fig. 11D, G ).

APERTURE ( Fig. 11D ). With semi-circular rounded base, funnel-shaped towards selenizone, convex shoulder, pointed at union with penultimate whorl, well rounded on parietal and columellar side. Lip sharp; protruding, oblique on columella with minor rib joining in v-shape with columellar keel ( Fig. 11G ); rounded towards base and parietal area with thin callus. Slit ¼ whorl deep with flattened sharp margins above and below, lip prosocline, union perpendicular to penultimate whorl ( Fig. 11E ). Callus thin; inside aperture smooth.

Anatomical description

Animal unknown; the soft parts of the live-collected specimen have been used for molecular analyses or retained in ethanol for future studies.

Habitat

Living on rocky surface with bacterial mats near active and inactive vents.

Distribution

Central and SE Indian Ridge, 23– 28° S, 69– 74° E, depth 2469–3296 m.

Remarks

The lack of distinct and regular spiral and or axial sculpture is uncommon. The outline is similar to that of Anatoma africanae (Herbert, 1963) from the Gallieni Fracture Zone, south of Madagascar at a depth of 400 m, but this species has a distinct and fine axial and spiral sculpture.

Figures

Fig. 11. Anatoma paucisculpta sp. nov. A–C. Paratype (SMF 358993), INDEX19_104RO (I19_Ma_91). H 0.77 mm, W 0.99 mm, Ha 0.61 mm, Wp 0.20 mm. D–H. Holotype (SMF 358992), INDEX15_62R (I15_Ma_169), H 1.03 mm, W 1.20 mm, Ha 0.70 mm, Wp 0.21 mm. Scale bars: 0.1 mm.