Semisulcospira watanabei Sawada, 2023

Sawada, Naoto & Fuke, Yusuke, 2023, Diversification in ancient Lake Biwa: integrative taxonomy reveals overlooked species diversity of the Japanese freshwater snail genus Semisulcospira (Mollusca: Semisulcospiridae), Contributions to Zoology 92 (1), pp. 1-37 : 26-28

Semisulcospira watanabei Sawada sp. nov.

[New Japanese name: Tokitama-kawanina] ( table 2 , supplementary table S2 ; figs 9 , 12K, L ) urn:lsid:zoobank.org:act:CA379B5F-390A-4369-A921-A65B6CCE33A2

Melania niponica – Martens, 1877: 116 (TAU).

Melania (Melanoides) niponica – Nevill, 1884: 264 (TAU).

Semisulcospira niponica – Kuroda, 1962: 86 (part; TAU).

Semisulcospira (Biwamelania) niponica – Nishino, 1991: 9–10, unnumbered figures (part); Kihira et al., 2009: 24–25 (part).

Semisulcospira (Biwamelania) niponica (ribbed type) – Watanabe & Nishino, 1995: 17–18, pl. 3, figs n–p (part).

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

Material examined: Holotype: KUZ Z4109, adult female with embryonic shells treated with sodium hypochlorite, collected from depth of 0.3 m of Lake Biwa at Kitakomatsu Port, Otsu City, Shiga Prefecture, Japan, on 28 November 2021 by first author . Paratypes: KUZ Downloaded from Brill.com 08/29/2023 02:12:56AM via free access

Z4110–Z4114, 4 adult females, 1 adult male, collected with holotype .

Additional materials: KUZ Z4115, 4 females, KUZ Z4116, 2 males, collected with type specimens; KUZ Z4117, 1 juvenile, collected from Oura on 28 November 2021 ; KUZ Z4118, 12 females, KUZ Z4119, 2 males, collected from Nihonmatsu on 24 January 2021; KUZ Z4120, 15 females, KUZ Z4121, 10 males, collected from Horikiri Port on 28 November 2021.

Etymology: The specific name is dedicated to Dr Naoshi Watanabe, who significantly contributed to the systematics of Semisulcospira in Lake Biwa.

Diagnosis: Viviparous semisulcospirid. Adult shell small (SH 26.8 ± 3.0, 25.0 ± 2.2 mm, BWL 15.9 ± 1.3, 14.8 ± 1.3 mm), nearly triangular to elongated (SA 21.1 ± 2.7, 20.5 ± 2.5 degrees); color in black or brown background; outer lip of aperture hardly swell (ASL 0.06 ± 0.05, 0.07 ± 0.04 mm); 2.8 ± 0.8, 2.9 ± 0.9 BCN; sculptures prominent, relatively few, ribbed on penultimate whorl (RN 11.1 ± 1.8, 10.1 ± 1.3); 4.6 ± 0.6, 4.4 ± 0.5 SCN; 1.7 ± 0.1, 1.8 ± 0.1 ASR; 2.8 ± 0.2, 3.0 ± 0.2 WER. Embryonic shell small, with distinct nodes on surface; color in black background or beige background with 1–3 brown or black bands.

Description of holotype: Adult shell ( fig. 9A–C ): AH 9.1 mm, AL 9.4 mm, ASR 1.57, AW 6.0 mm, BCN 2, BWL 16.1 mm, FWL 3.4 mm; NL 0 mm; PWL 6.3 mm, RN 11, SA 23.4 degrees, SH 25.0 mm, SW 11.0 mm, TWL 4.5 mm, WER 2.67; WN 3.50; shell nearly thick triangular; suture hardly undulating; whorl sides slightly convex; swell of outer lip of aperture absent; sculpture prominent, almost straight, vertical to oblique, fully ribbed in shell apex to body whorl, faded in body whorl near aperture, spiral striae absent; apex of shell eroded; shell colored black background without color band.

Operculum ( fig 9D ): 6.5 mm in long diameter; nearly egg-shaped subcircular, paucispiral, comprising around 3 whorls; nucleus subcentral.

Embryonic shells ( fig 9E–G ): EN 81, RNE 11, SHE 2.3 mm, SWE 1.8 mm, WNE 3; shell globose; suture moderately depressed by discrepancy in adjacent whorls; nodes remarkable, on central part of whorls, keels weak, on lower part of whorls; shell colored blackish beige background with 3 brown or 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 2–3 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 3.5 times longer than other triangular cusps; central denticle of lateral irregular triangular, teeth about 2.5 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. 9M, O, R ): Measurements and counts shown in table 2 and supplementary table S2 . Shell nearly slightly elongated triangular; suture hardly to slightly undulating; whorl sides hardly to slightly convex; outer lip of aperture hardly to slightly swell; longitudinal ribs distinct, slightly curved, vertical to oblique, on upper to body whorl; spiral cords indistinct, sometimes absent; shell colored black to brackish brown or beige in background, rarely indistinct brown band on lower part of each whorl and/ or basal part of shell; surface of shells covered with thin algae layer before treatment.

Operculums ( fig. 9I, L, N, P, S ): 5.5–8.2 mm in long diameter.

Embryonic shells ( fig. 9J, Q, T ): Measurements and counts shown in table 2 and supplementary table S2 . Shell colored blackish brown background or beige background with 1–3 brown or black bands on upper and/or lower part of each whorl and/or on basal part of shell.

Radulae ( fig. 12K, L ): Lateral teeth with 2–4 inner and outer pointed cusps; central denticle of rachidian about 3.5 to 5.5 times longer than other triangular cusps; central denticle of lateral teeth about 2.5 to 3.0 times longer than other triangular cusps; 4–6 rounded denticles in interior and exterior marginal teeth.

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 the new species is discrete and limited to four sites in the coast of Lake Biwa ( fig. 1 ). However, the species may be widespread on the Northern shore of the lake because the ribbed type of S. niponica , whose sculpture type is consistent with S. watanabei sp. nov. has been recorded there ( Watanabe & Nishino, 1995, fig. 5b, S . (B.) niponica ribbed). Semisulcospira watanabei inhabits shallow rocky areas and concrete blocks around harbours. The new species was found with S. niponica at Kitakomatsu Port and with S. fuscata at Oura and Nihonmatsu. Semisulcospira watanabei sp. nov. was collected with other Lake Biwa species: S. habei at Oura, Nihonmatsu, and Horikiri Port; S. decipiens at Oura and Nihonmatsu.

Remarks: The new species was first described as an intraspecific variation of S. niponica by Watanabe and Nishino (1995). Semisulcospira watanabei sp. nov. can be discriminated from S. niponica in the smaller size of the adult and embryonic shell and fewer prominent longitudinal ribs on the shell surface. Traits of a blackish, elongated triangular adult shell, prominent longitudinal ribs, and globose embryonic shells with several brown bands distinguish S. watanabei sp. nov. from other Semisulcospira species (supplementary fig. S1 ).

Figures

FIGURE 1 Map of Lake Biwa (A) and Oura Bay (B) showing 15 sampling localities:blue, Semisulcospira niponica; green, S.fuscata; purple, S.watanabei sp.nov.; red, S.nakanoi sp.nov.; orange, S.salebrosa sp.nov; black, putative hybrid between S.fuscata and S.watanabei sp.nov.

FIGURE 5 Phylogenetic relationships of five Semisulcospira species estimated by the Neighbor-Net reconstructed based on uncorrected p-distances of 738 SNPs

FIGURE 9 Shells of Semisulcospira watanabei sp. nov.A–G, Holotype, KUZ Z4109. H–J, Paratype, KUZ Z4110.K–L, Paratype, KUZ Z4114.M–N.Specimen from Oura, KUZ Z4117.O–Q, Specimen from Nihonmatsu, KUZ Z4118.R–T, Specimen from Horikiri Port, KUZ Z4120.A–C, H, K, M, O, R, Adult shell.A–C, H, O, R, Female.K, Male. M, Juvenile.D, I, L, N, P, S, Operculum. E–G, J, Q,T, Embryonic shell. Scale bars: 10mm (A–D, H–I, K–L, M–N, O–P, R–S), 1 mm (E–G, J, Q, T). All specimens were treated with 3% sodium hypochlorite

FIGURE 12 Radulae of Semisulcospira species.A–G, Semisulcospira niponica: A, Oura Port, KUZ Z4091; B, Nagahama Port, KUZ Z4093; C, Iso, KUZ Z4095; D, Kitakomatsu Port, KUZ Z4097; E, Katata Port, KUZ Z4099; F, Otsu Port, KUZ Z4101; G, Nango, KUZ Z4103.H–J, Semisulcospira fuscata: H, Lake Yogo, KUZ Z4103; I, Oura, KUZ Z4105; J, Nihonmatsu, KUZ Z4107.K–L, Semisulcospira watanabei sp. nov.:K, Kitakomatsu Port, KUZ Z4115;L, Horikiri Port, KUZ Z4120.M–N, Semisulcospira nakanoi sp. nov.: M, Onoe Port, KUZ Z4129;N, Chikubu-shima Island, KUZ Z4127.O–P, Semisulcospira salebrosa sp. nov.:O, Take-shima Island, KUZ Z4138;P, Shiraishi-jima Island, KUZ Z4136.Scale bars:100 Μm