Semisulcospira salebrosa Sawada 2023, sp. nov.

Semisulcospira salebrosa Sawada sp. nov.

[New Japanese name: Konpeito-kawanina] (table 2, supplementary table S2; figs 11, 12O, P) urn:lsid:zoobank.org:act: 003C4CE6-596C-4F67-8C30-E5A51DC88B37

Semisulcospira niponica – Watanabe, 1984: fig. 3c–d, g–h.

Semisulcospira (Biwamelania) niponica – Nishino, 1991: 9–10, unnumbered figures (part); Kihira et al., 2009: 24–25, unnumbered figure (part); Miura et al., 2019: fig. S1d, e.

Biwamelania nipponica – Minato, 1991: 79, unnumbered figure.

Semisulcospira (Biwamelania) niponica (biwae type) – Watanabe & Nishino, 1995: 17–18, fig. 5b (part).

Biwamelania niponica – Nishino & Tanida, 2018: 56, 251, unnumbered figure (part).

Material examined: Holotype:KUZ Z4131, adult female with embryonic shells treated with sodium hypochlorite, collected from a depth of 3.0 m of Lake Biwa at Shiraishi-jima Island, Takashima City, Shiga Prefecture, Japan, on 9 September 2020 by first author. Paratypes: KUZ Z4132–Z4135, 3 adult females, 1 adult male, collected with holotype.

Additional materials: KUZ Z4136, 11 females, KUZ Z4137, 3 males, collected with type specimens; KUZ Z4138, 15 females, KUZ Z4139, 10 males, collected from Take-shima Island on 25 July 2021.

Etymology: The specific name is after prominent granulated longitudinal ribs on adult shells of the new species.

Diagnosis: Viviparous semisulcospirid. Adult shell large (SH 35.7 ± 2.0, 27.6 ± 4.9 mm, BWL 21.9 ± 1.5, 16.6 ± 2.8 mm), nearly triangular (SA 21.2 ± 2.5, 21.5 ± 4.6 degrees); color in black background; outer lip of aperture prominently swell (ASL 0.44 ± 0.12, 0.33 ± 0.14 mm); 2.5 ± 0.7, 2.3 ± 0.5 BCN; ribs relatively few, prominently nodulated on penultimate whorl (RN 11.1 ± 1.6, 10.6 ± 1.4); 3.4 ± 0.7, 3.2 ± 0.4 SCN; 1.6 ± 0.1, 1.6 ± 0.1 ASR; 3.0 ± 0.3, 3.2 ± 0.6 WER. Embryonic shell medium sized, with distinct nodes on surface; color in beige background with 3–4 brown or black bands.

Description of holotype: Adult shell (fig. 11A–C): AH 14.2 mm, AL 14.5 mm, ASR 1.63, AW 8.9 mm, BCN 3, BWL 23.0 mm, FWL 5.3 mm; NL 0.42 mm; PWL 8.2 mm, RN 9, SA 18.5 degrees, SCN 3, SH 39.4 mm, SW 15.7 mm, TWL 6.6 mm, WER 2.71; WN 4.75; shell near slightly elongated triangular; suture hardly undulating; whorl sides slightly convex; outer lip of aperture swell prominently; longitudinal ribs slightly curved, straight, nodulated prominently in upper to body whorl; apex of shell eroded; shell colored black background without color band.

Operculum (fig. 11D): 8.8 mm in long diameter; nearly egg-shaped subcircular, paucispiral, comprising around 3 whorls; nucleus subcentral.

Embryonic shells (fig. 11E–G): EN 30, RNE 12, SHE 2.7 mm, SWE 2.5 mm, WNE 2.5; shell globose; suture prominently undulating; remarkable nodes present on central part of whorls, keels absent on lower part of whorls; shell colored beige background with 3 black bands on upper and/or lower part of each whorl and/or on basal part of shell.

Radula: Taenioglossa consisting of rachidian in single, lateral teeth, interior and exterior marginal teeth in double row. Rachidian roughly triangular with large central denticle and 2 minor pointed triangular cusps on each side. Lateral teeth with large central denticle, 2–3 inner and outer pointed cusps. Central denticle tip of rachidian and lateral teeth mostly flat, rarely pointed; central denticle of rachidian approximately regular triangular, about 3.0 times longer than other triangular cusps; central denticle of lateral teeth irregular triangular, about 3.5 times longer than other triangular cusps. Interior and exterior marginal teeth spoon-shaped with 4–5 rounded denticles.

Reproductive organ: Female: Long narrow oviduct, entering near seminal receptacle with long protrusions. Ventral edge of spermatophore bursa with curved sperm gutter, extending toward mantle cavity. Brood pouch on dorsal side of spermatophore bursa, inflated dorsally, separated into many cells, including eggs and embryos; eggs and embryos radially developing from base of brood pouch near seminal receptacle and embryos in anterior or dorsal cells more developed.

Variation: Adult shells (fig. 11M): Measurements and counts shown in table 2 and supplementary table S2. Shell nearly triangular to slightly elongated; suture slightly to moderately undulating; whorl sides slightly to moderately convex; sculptures prominent, almost straight to slightly curved, vertical to slightly oblique, prominently nodulated, rarely ribbed on upper whorls; shell colored black to brackish brown background with or without several color bands on upper, middle, and lower part of each whorl and basal part of shell; surface of shells covered with thin algae layer before treatment.

Operculums (fig. 11I, L, N): 8.8–11.1 mm in long diameter.

Embryonic shells (fig.11J, O):Measurements and counts shown in table 2 and supplementary table S2. Suture slightly or prominently undulating; distinct keels present or absent on lower part of whorls; shell colored beige background with 3 brown or black bands on upper and/or lower part of each whorl and/or on basal part of shell.

Radulae (fig. 12O, P): 2–4 minor pointed triangular cusps on each side of rachidian; lateral teeth with 1–4 inner and outer pointed cusps; central denticle of rachidian about 2.5 to 5.0 times longer than other triangular cusps; central denticle of lateral teeth about 1.5 to 3.0 times longer than other triangular cusps.

Reproductive organs: Male: Gonad consisting of testes, vas deferens, and prostate without penis. Posterior ventral part of inflated prostate with deep groove, forming U-shape in transverse section. Anterior prostate narrowly opening to mantle cavity.

Distribution and ecology: The known distribution of S. salebrosa sp. nov. is restricted to Shiraishi-jima Island and Take-shima Island in Lake Biwa (fig. 1). The new species inhabits the wharf and rocky bottom of the islands. Semisulcospira salebrosa sp. nov. was found

with S. shiraishiensis in the Shiraishi-jima Island and S. takeshimensis in Take-shima Island.

Remarks: The new species has been identified as S. biwae together with S. nakanoi sp. nov. and assigned as an intraspecific variation of S. niponica. The new species can be discriminated from S. nakanoi sp. nov. and other semisulcospirids by the large, blackish, triangular adult shell with well-granulated ribs and strongly undulating outer lip of the aperture and globose embryonic shells with several brown bands (supplementary fig. S1).