Provanna exquisita, Chen & Watanabe, 2022

Chen, Chong & Watanabe, Hiromi Kayama, 2022, A new provannid snail (Gastropoda, Abyssochrysoidea) discovered from Northwest Eifuku Volcano, Mariana Arc, ZooKeys 1112, pp. 123-137 : 123

Provanna exquisita sp. nov.

Figs 2A-D , 3A-D

Provanna aff. fenestrata - Giguère and Tunnicliffe 2021: supplementary table S2

Type locality.

Hydrothermal vent near the summit of Northwest Eifuku Volcano ( Lupton et al. 2006; Rossi 2016) on the Mariana Arc; 21°29.2567'N, 144°02.4813'E, 1606 m deep ("Golden Lips" site 40 m away from the Champagne vent). Habitat temperature 2.7 °C, sulfide level negligible. ROV JASON II dive #799, 2014/xii/14, R/V Roger Revelle cruise RR1413 "Submarine Ring of Fire 2014 - Ironman".

Type material.

Holotype (Fig. 2A ), MNHN-IM-2000-37945; SH 10.4 mm, SW 9.0 mm, AH 6.1 mm, AW 4.5 mm. Paratype #1 (Fig. 2B ), NSMT-Mo 79360; SH 11.6 mm, SW 10.3 mm, AH 7.1 mm, AW 5.6 mm. Paratype #2 (Fig. 2C , Fig. 3A-D ), MNHN-IM-2000-37946; SH 13.1 mm, SW 9.4 mm; aperture damaged, soft parts extracted and used for DNA barcoding and dissected for SEM. Paratype #3 (Fig. 2D ), NSMT-Mo 79361; SH 9.4 mm, SW 7.2 mm; aperture broken. All type material were live collected from the type locality and preserved in 75% ethanol.

Diagnosis.

A large Provanna reaching over 13 mm in shell height (exceeds 15 mm if spire intact), teleoconch whorls with two or three sharply raised, flange-like spiral keels crossing with weaker axial ribs to form a regularly latticed sculpture.

Description.

Shell (Fig. 2 ). Teleoconch thin and fragile, translucent, thickened where ribs or keels occur. Whorls highly convex, inflated for its genus. Suture distinct, well defined, impressed. Spiral sculpture of 2 or 3 very strong, sharply raised, approximately equally-spaced blade or flange-like keels, positioned at shoulder, mid-whorl, just above suture. Some individuals lack shoulder keel; other 2 always present. Three additional weaker spiral ribs present anterior to suture. Axial sculpture of 14-18 regularly spaced, raised ribs running from suture to suture, approximately equal in strength. Together two directions of ribs intersect to form regular reticulate sculpture of regular rectangles. Nodes drawn out on spiral keels where intersection with axial ribs occur, resulting in undulated edges, on shoulder keel these develop into short spines. Aperture semicircular, taller than wide. Columellar variable from straight to sigmoidal. Siphonal notch distinct, shallow. Apex decollate, heavily corroded, leaving only 1.5-2.5 whorls of teleoconch whorls. Incompletely corroded periostracum present around apex, darkened in colouration. Secondary plug-like calcareous secretion present at apex, preventing exposure of visceral mass. Growth lines indistinct. Protoconch unknown, as all specimens examined had corroded spire.

Periostracum thick, golden brown.

Operculum (Fig. 3D ) present. Paucispiral, oval, bluntly pointed. Nucleus eccentric, 3.5 whorls. Yellowish-brown in colour, thin, semitransparent.

Radula (Fig. 3A-C ) taenioglossate, formula 2 + 1 + 1 + 1 + 2. Central tooth solid, with single triangular, bluntly pointed, overhanging main cusp. Solid lateral support ridges present on both sides of central supporting ridge. Shaft with 2 sharp protrusions at anterior edge of lateral support ridge. Lateral teeth solid, inner edge sigmoidal. Laterals with 5 cusps, main cusp triangular, bluntly pointed. One moderately strong inner cusp inside main cusp, 3 weaker cusps outside main cusp. Sharply raised protrusion present on shafts of laterals below main cusp. Marginal teeth flat, broad, truncated distally. Distal tip rake-like, finely serrated into c. 22-24 denticles, outermost strongest. Further c. 10-12 minor denticles present on outermost cutting edge, below strongest cusp.

Gross external anatomy examined to limited extent with 2 brittle, ethanol-preserved specimens, revealing no notable deviations from published accounts for its genus ( Warén and Ponder 1991; Chen et al. 2019). Animal occupied approximately 1.5-2 whorls. Head with flattened snout, 1 pair of equally sized, tapering cephalic tentacles present; eyes lacking. Penis, neck furrow, epipodial tentacles lacking. Pallial edge smooth. Gill monopectinate, typical for its genus, not hypertrophied. Apex of visceral mass occupied by gonad, posterior of digestive gland.

Distribution.

So far, it is only known from a hydrothermal vent field on the summit of Northwest Eifuku Volcano, Mariana Arc. In addition to the Golden Lips site where specimens were collected, it has also been visually confirmed from the Champagne site 40 m away (Fig. 1B ).

Etymology.

Exquisita (Latin, feminine adjective in the nominative singular), meaning “inquiring” or “exquisite”.

Remarks.

The striking shell sculpture of Provanna exquisita sp. nov., especially the prominent sharply raised spiral keels, is unique among described Provanna species. The species with the closest morphology is Provanna fenestrata Chen, Watanabe & Sasaki, 2019 described from Okinawa Trough vents and also recently reported from a methane seep in the South China Sea ( Chen et al. 2019; Ke et al. 2022), which also has a similar coarse, regular, lattice-like sculpture. In P. fenestrata , however, the spiral and axial ribs are of similar strength and spiral ribs do not form raised keels; nodes at the intersection between the two nodes are also lacking in P. fenestrata ( Chen et al. 2019). In individuals of P. fenestrata with 2 spiral ribs, it is always the mid-whorl spiral rib that is missing, whereas the missing spiral keel is always the posterior-most shoulder keel in P. exquisita sp. nov. Furthermore, the periostracum of P. fenestrata is yellowish green compared to golden brown in P. exquisita sp. nov. The radulae of the two species are similar, although in P. fenestrata the central and lateral teeth have sharper cusps and the marginals are less serrated (12-14 vs 22-24 denticles).

A number of other Provanna species also exhibit reticulate shell sculpture, including P. clathrata Sasaki, Ogura, Watanabe & Fujikura, 2016 from Okinawa Trough vents, Provanna pacifica (Dall, 1908) from seeps in Gulf of Panama and Oregon Margin, Provanna muricata Warén & Bouchet, 1986 from Galápagos Rift vents, P. admetoides Warén & Ponder, 1991 from Florida Escarpment seeps, P. segonzaci Warén & Ponder, 1991 from Lau Basin vents, Provanna buccinoides Warén & Bouchet, 1993 from Lau and North Fiji vents, and Provanna reticulata Warén & Bouchet, 2009 from seeps off West Africa. However, compared to P. exquisita sp. nov. all of these species exhibit much weaker spiral sculpture ( Warén and Bouchet 1986, 2001, 2009; Warén and Ponder 1991; Sasaki et al. 2016). The spiral ribs of P. muricata are much weaker than the axial ones, which is opposite to the pattern seen in P. exquisita sp. nov. ( Warén and Bouchet 1986). The radulae of P. pacifica and P. admetoides exhibit slender, reduced central teeth and are very different from the solid central tooth in P. exquisita sp. nov. ( Warén and Bouchet 1986; Warén and Ponder 1991).

Figures

Figure 1. In situ habitat of Provanna exquisita sp. nov. on the summit of Northwest Eifuku Volcano. A overview of the habitat showing dominance by the deep-sea mussel Bathymodiolus septemdierum B close-up of the mixed provannid aggregation, arrowheads indicate examples of P. exquisita sp. nov. Photos taken by ROV ROPOS on dive 792 in Champagne vent, 21 ° 29.25 ' N, 144 ° 02.49 ' E, 1608 m deep.

Figure 2. Provanna exquisita sp. nov., type specimens A-D holotype (MNHN-IM- 2000 - 37945), shell height 10.4 mm E-H paratype 1 (NSMT-Mo 79360), shell height 11.6 mm I, J paratype 2 (MNHN-IM- 2000 - 37946), shell height 13.1 mm K, L paratype 3 (NSMT-Mo 79361), shell height 9.4 mm. Scale bar: 1 cm, applies to all parts of the figure.

Figure 3. Provanna exquisita sp. nov., scanning electron micrographs A radula overview B close-up of central and lateral teeth C close-up of marginal cusps D operculum. Scale bars: 100 μm (A); 20 μm (B); 50 μm (C); 1 mm (D).