Semisulcospira nishimurai Sawada, 2024

Sawada, Naoto, Fuke, Yusuke, Miura, Osamu, Toyohara, Haruhiko & Nakano, Takafumi, 2024, Redescription of Semisulcospira reticulata (Mollusca, Semisulcospiridae) with description of a new species from Lake Biwa, Japan, Evolutionary Systematics 8 (1), pp. 127-144 : 127-144

Semisulcospira nishimurai Sawada sp. nov.

Table 4 , Figs 7 Z – BG, 8 E – I, 9 A, B, D – F New Japanese name: Azai-kawanina

Melania niponica – Kobelt 1879: 131, pl. 19, fig. 11 (part).

Melania multigranosa – Annandale 1916: 44–45, pl. 3, fig. 2 B (part).

Melanoides (Semisulcospira) multigranosa – Kuroda 1929: 186, 189, pl. 5, fig. 36 (part).

Semisulcospira (Biwamelania) sp. – Nishimura 2024: unnumbered figures (part).

Material examined.

Holotype. KUZ Z 4935 , adult female, collected from Lake Biwa at a water depth of 3 m, Hannoura , Kinomoto-cho, Nagahama City, Shiga Prefecture, Japan on 26 June 2022 by Naoto Sawada .

Paratypes. KUZ Z 4936 – Z 4938, 3 adult females, Z 4939, 1 adult male collected from 3–6 m depths with holotype .

Additional materials.

KUZ Z 4940 , 11 females, Z 4941, 11 males, collected from 2–7 m depths with holotype ; KUZ Z 4946 , 15 females, Z 4947, 13 males, collected from 1–8 m depths at Minamihama on 2 July 2022 ; KUZ Z 4952 , 14 females, Z 4953, 5 males, from 1–7 m depths at Kitafunaki on 10 July 2022 ; KUZ Z 4945 , 2 females, from 0–1 m depths from Oura Port on 28 November 2021 ; KUZ Z 4957 , 3 females from 6–8 m depths at the coast of Oki-shima Island on 10 August 2019 .

Diagnosis.

Viviparous. Teleoconch elongated, medium sized in the genus [SH 30.7 ± 3.3 (mean ± SD) (female), 27.4 ± 3.3 (male) mm; BWL 15.9 ± 1.7, 14.5 ± 1.6 mm], spires laterally broadened (SA 17.3 ± 2.4, 17.6 ± 2.4 degrees), axially compressed (WER 2.4 ± 0.2, 2.5 ± 0.2); outer lip of aperture simple, smooth; aperture rounded (ASR 1.6 ± 0.1, 1.7 ± 0.1); basal cords few (BCN 2.9 ± 0.6, 3.1 ± 0.8); longitudinal ribs, distinct, granulated on penultimate whorl, in medium number (RN 20.4 ± 3.7, 18.2 ± 2.4); spiral cords in medium number (SCN 6.3 ± 0.7, 5.8 ± 0.5); color in light brown background. Protoconch small to medium sized in the genus (SLP 2.4 ± 0.3 mm, WNP 3.2 ± 0.3); longitudinal ribs prominently granulated; color in light beige, with or without 1–2 brown bands.

Description of holotype

( KUZ Z 4935 ; Fig. 7 Z – AF). Teleoconch. AH 10.2 mm, AL 10.4 mm, ASR 1.60, AW 6.5 mm, BCN 3, BWL 17.1 mm, FWL 4.2 mm, PWL 6.5 mm, RN 26, SA 16.3 degrees, SH 35.0 mm, SW 11.9 mm, TWL 5.0 mm, WER 2.40, WN 6.50; shell elongated; spires moderately broadened laterally, moderately convex; suture strongly undulating; outer lip of aperture simple, smooth; aperture rounded; apex of shell eroded; longitudinal ribs distinct, oblique, opisthocyrt, almost smooth; spiral cord absent on penultimate whorl; shell colored light yellowish-brown background in upper, yellowish-brown background in lower whorls with dark brown longitudinal stripes; color bands absent.

Operculum. 7.0 mm in long diameter; nearly egg-shaped subcircular, paucispiral, comprising around 3 whorls; nucleus subcentral.

Protoconchs. PN 61, RNP 13, SLP 2.4 mm, SWP 1.9 mm, WNP 3.25; shell globose; suture prominently depressed by discrepancy between adjacent whorls; longitudinal ribs remarkable, with pointed nodes in 1 row on central part of whorls; spiral cord distinct on upper and lower parts of whorls; shell colored beige in background, without color band.

Radulae (Fig. 8 E ). Taenioglossa. Rachidian teeth consisting of central denticle and 2–3 small pointed triangular cusps on each side; tip of rachidian central denticle narrow, pointed, triangular, 2.5 times longer than other triangular cusps. Lateral teeth consisting of large central denticle and 2–3 inner and outer pointed cusps; central cusp of lateral teeth narrow, pointed, triangular, 2.0 times longer. Interior and exterior marginal teeth spoon-shaped with 4–5, 4 rounded denticles, respectively.

Reproductive organ. Female. Oviduct long, narrow, emerging from ovary entering near seminal receptacle on ventral side of soft body; protrusions of seminal receptacle long. Sperm gutter extending from spermatophore bursa towards mantle cavity, curved inward along whorls. Brood pouch extending along dorsal side of spermatophore bursa and sperm gutter, dorsally inflated, separated into many chambers, including eggs and embryos; eggs colored beige, radially developing from base of brood pouch near seminal receptacle.

Variation.

Teleoconchs (Fig. 7 AG, AJ, AM, AP, AR, AU, AX, AZ, BC, BE). Measurements and counts shown in Table 4 . Spires broadened slightly to moderately; slightly to strongly convex; suture slightly to moderately undulating; longitudinal ribs distinct, oblique, typically orthocline to opisthocyrt on upper whorls, opisthocyrt on lower whorls, mildly to prominently granulated at intersection with spiral cords, rarely opisthocline on upper and lower whorls, fade on body whorl; spiral cords sometimes indistinct; shell colored yellowish-brown to light brown with dark brown longitudinal stripes; color bands dark brown or dark olive, rarely present on central part of upper whorls.

Opercula (Fig. 7 AH, AK, AN, AQ, AS, AV, AX, BA, BD, BF). 5.1–8.2 mm in long diameter.

Protoconchs (Fig. 7 AI, AL, AO, AT, AW, BB, BG). Measurements and counts shown in Table 4 . Shell globose or slightly elongated; suture slightly to moderately undulating; longitudinal ribs remarkable, usually granulated pointedly on central part of whorls in 1–2 rows; spiral cord distinct or weak on upper and lower part of whorls; shell colored beige to light beige in background; color bands, brown, thick, sometimes present on upper and lower parts of whorls and on basal part.

Radulae (Fig. 8 F – I ). Rachidian teeth consisting of 5–8 triangular cusps; tip of rachidian central denticle typically narrow, pointed, rarely rounded, 2.0–3.0 times longer than other triangular cusps. Central cusp of lateral teeth typically narrow, pointed, rarely wide, rounded, 1.0–3.5 times longer than other triangular cusps than other triangular cusps. Interior and exterior marginal teeth spoon-shaped with 4–6, 4–5 rounded denticles, respectively.

Reproductive organs. Female (Fig. 9 A, B, D ). Protrusions of seminal receptacle rarely short.

Male (Fig. 9 E, F ). Vas deferens long, narrow, emerging from testes, entering posterior end of prostate. Prostate without penis elongated, inflated in posterior ventral part, with deep groove, forming U-shape in transverse section, anterior narrowly opening to mantle cavity.

Etymology.

The specific name is dedicated to Toshiaki Nishimura, who first discovered the new species through his exhaustive survey of the distribution of Semisulcospira in Lake Biwa ( Nishimura 2024). The new Japanese name refers to the Azai clan, a Japanese daimyo (feudal lord) of the Sengoku period, whose largest territory roughly corresponds to the distribution of the new species ( Ota 2011).

Distribution and ecology.

Semisulcospira nishimurai sp. nov. is widely distributed in the northern basin of Lake Biwa (Fig. 1 ). The new species was found on sandy mud to mud bottoms at depths of 1–8 m and was common at depths greater than 3 m. The new species was collected with other congeners: S. niponica - group, S. decipiens at Hannoura and Kitafunaki, S. watanabei at Hannoura and Oura Port, S. niponica at Oura Port and Oki-shima Island, S. reticulata at Hannoura and Kitafunaki; S. nakasekoae - group, S. cryptica , S. ourensis , and S. morii at Hannoura, S. arenicola and S. elongata at Minamihama and Kitafunaki, S. davisi at Hannoura, Minamihama, and Kitafunaki. This new species was found with S. reiniana at Kitafunaki.

Remarks.

The new species has been confused with S. niponica and S. multigranosa . However, the new species can be discriminated from other congeners, including S. niponica and S. multigranosa , by the combination of an elongated teleoconch with a medium to large number of weakly granulated longitudinal ribs and a medium-sized, granulated, beige-coloured protoconch. Although S. nishimurai sp. nov., S. decipiens , and S. reticulata possess partially similar teleoconch morphologies, the larger number of longitudinal ribs and lower spire angle of teleoconchs discriminate the new species from S. decipiens . The new species can be distinguished from S. reticulata by its smaller numbers of longitudinal ribs on teleoconchs and smaller protoconchs.

Figures

Figure 1. Map representing seven localities where Semisulcospira reticulata (purple) and S. nishimurai sp. nov. (red) were collected in Lake Biwa, Japan. The detailed localities are shown in Table 1.

Figure 7. Shells and opercula of Semisulcospira reticulata (A – Y) and S. nishimurai sp. nov. (Z – BF). A – F. Holotype of S. reticulata from Oki-shima Island (offshore), NSMT - Mo 39770; G – J. Hannoura, KUZ Z 4926, Z 4927; K – O. Kitafunaki, KUZ Z 4930, Z 4931; P – T. Oki-shima Island (offshore), KUZ Z 4925; U – Y. Mano, KUZ Z 4229, Z 4286; Z – AF. Holotype of S. nishimurai sp. nov. from Hannoura, KUZ Z 4935; AG – AQ. Paratypes of S. nishimurai sp. nov. from Hannoura, KUZ Z 4936 – Z 4939; AR – AT. Oura Port, KUZ Z 4945; AU – AY. Minamihama, KUZ Z 4946, Z 4947; AZ – BD. Kitafunaki, KUZ Z 4952, Z 4953; BE – BG. Oki-shima Island (coast), KUZ Z 4957. Scale bars: 10 mm (1), female teleoconch (A – C, G, K, P, S, U, Z – AB, AG, AJ, AM, AR, AU, AZ, BE), male teleoconch (J, N, AP, AX, BC), operculum (H, L, O, Q, T, V, Y, AC, AH, AK, AN, AQ, AS, AV, AY, BA, BD, BF); 2 mm (2), protoconch (D – F, I, M, R, W); 1 mm (2), protoconch (AD – AF, AI, AL, AO, AT, AW, BB, BG).

Figure 8. Radulae of Semisulcospira reticulata (A – D) and S. nishimurai sp. nov. (E – I). A. Hannoura, KUZ Z 4926; B. Kitafunaki, KUZ Z 4930; C. Oki-shima Island (offshore), KUZ Z 4925; D. Mano, KUZ Z 4229; E. Holotype of S. nishimurai sp. nov. from Hannoura, KUZ Z 4935; F. Oura Port, KUZ Z 4945; G. Minamihama, KUZ Z 4946; H. Kitafunaki, KUZ Z 4952; I. Oki-shima Island (coast), KUZ Z 4957. Scale bars: 100 μm.

Figure 9. Schematic drawings indicating generalised external features of the soft body and reproductive organs of Semisulcospira reticulata and S. nishimurai sp. nov.: A, B. Dorsal and ventral views of organs in visceral mass of mature female of S. nishimurai sp. nov. without operculum; C. External, right lateral view of pallial oviduct of S. reticulata; D. External, view of pallial oviduct of S. nishimurai sp. nov.; E. External, right upper lateral view of the prostate of S. nishimurai sp. nov.; F Internal folding structures of the prostate of S. nishimurai sp. nov. Abbreviations: bp, brood pouch; ct, ctenidium; dg, digestive gland; eg, egg; em, embryo; f, foot; inn, inner wall of brood pouch; int, intestine; kd, main kidney chamber; os, osphradium; ov, ovary; ovi, renal oviduct; pr, prostate; rcs, seminal receptacle; sg, sperm gutter; sn, snout; spb, spermatophore bursa; ss, style sac; sto, stomach; t, cephalic tentacle; vd, vas deferens. Scale bars: 5 mm.