Semisulcospiridae Morrison, 1952

Sawada, Naoto & Nakano, Takafumi, 2021, Saphonecrus gilvus Melika and Schweger 2015, Zoological Studies (Zool. Stud.) 60 (7), pp. 1-11 : 3-9

Family Semisulcospiridae Morrison, 1952 Genus Semisulcospira Boettger, 1886 Semisulcospira multigranosa ( Boettger, 1886) ( Fig. 3 )

Melania (Semisulcospira) multigranosa Boettger, 1886: 7–8 (part).

Melania multigranosa – Pilsbry 1902: 119–120 (in part); Annandale 1916: 44–46, 55, 59, pl. 3, fig. 2A–E (part).

Semisulcospira multigranosa – Kuroda 1929: 186, 189, pl. 5, figs. 34–36 (part); Fukuoka 1933: 114, 115, fig. 4.

Semisulcospira decipiens Kuroda 1941: 184 (part); Habe 1961: 25, pl. 11, fig. 9 (part); Habe and Kosuge 1967: 28, pl. 11, figs. 19, 20.

Material examined: Lectotype: SMF225654, adult shell, sex undetermined, collected from rice field near Lake Biwa in central Honshu island, Japan in 1885 by [P.] B. Schmacker.

Paralectotypes: 37 specimens collected in and around Lake Biwa in 1885 by [P.] B. Schmacker: SMF 225655, 3 specimens; SMF 225656, 1; 225657, 1; 225658, 16; 225659, 2; 225660, 6; 358291, 3; 358294, 1; 358295, 1; 359900, 3. SMF 225655, 225658, 359900 from rice field near Lake Biwa; SMF 225656, 225659, 358291, 358294 from creek close to the lake; SMF 225657, 225660, 358295 from Lake Biwa.

Amended diagnosis: Adult shell elongated; 3–4 BCN, around 17–19 curved ribs with distinct or indistinct nodes; 5–6 SCN; 18.1–20.5 degrees SA; 1.7– 1.8 ASR; 2.4–2.9 WER.

Description: Lectotype: AH 9.1 mm, AL 8.8 mm, ASR 1.7, AW 5.3 mm, BCN 3, BWL 14.4 mm, FWL 3.1 mm, PWL 5.4 mm, RN 17, SA 19.0 degrees, SCN 5, SH 27.3 mm, SW 9.3 mm, TWL 4.1 mm, WER 2.9, WN 5.0; shell elongated, suture slightly undulating, sides of whorls moderately convex, slightly curved longitudinal ribs partly nodulate in third to body whorl; ribs fade in body whorl; apex of shell eroded; shell surface colored brown to blackish brown with deposits; without operculum.

Paralectotypes: only four specimens in good condition examined. SMF 225655, 3 specimens; SMF 225656, 1. AH 7.6–8.1 mm, AL 7.9–8.4 mm, ASR 1.7– 1.8, AW 4.6–5.0 mm, BCN 3–4, BWL 12.7–13.4 mm, FWL 3.0– 3.5 mm, PWL 4.5–5.3 mm, RN 17–19, SA 18.1–20.5 degrees, SCN 5–6, SH 24.6–26.6 mm, SW 8.5–8.9 mm, TWL 3.6–4.3 mm, WER 2.2–2.6, WN 4.5–6.5; shell elongated, suture slightly to moderately undulating, sides of whorls slightly convex, moderately curved longitudinal ribs hardly or partly nodulated and fade in penultimate to body whorl in some specimens; apex of shell eroded; shell surface and operculums partly colored brown to blackish brown with deposits; operculum nearly pear to egg-shaped subcircular, paucispiral, nucleus subcentral.

Remarks: Among the paralectotypes of S. multigranosa, SMF 225657, 225660, 358291, 358294, 358295, 359900 may contain specimens that are actually other semisulcospirid species. SMF 225657 and 225660 can be identified as Koreoleptoxis tegulata ( Martens, 1894) according to their smaller SL of the well-developed adult shells (about 16 mm) with moderately convex whorl sides, fewer distinguished longitudinal ribs from upper to lower whorls (about 16 RN), inconspicuous basal cords (3–4 BCN), and smaller SA (about 17 degrees). SMF 358291 and 358295 may belong to S. reiniana (Brot in Kobelt, 1876) in having more basal cords (7–8 BCN) and well-developed longitudinal ribs. SMF 358294 and 359900 may be S. decipiens in having smaller SA (about 17 degrees) and fewer basal cords (3 BCN).

The original description stated that the type specimens were collected mainly from rice fields and creeks close to Lake Biwa ( Boettger 1886). However, the snails whose adult shell morphology corresponds to S. multigranosa have never been found in such habitats around the lake after Boettger (1886), but they have been collected from inside the lake (e.g., Kuroda 1929; Fukuoka 1933; Watanabe 1970a). Since the type series also includes specimens that can be identified as Korean species with characteristics of SL, RN, BCN, SA, and shape of whorl sides, the original material of S. multigranosa may be composed of specimens collected from several locations in Japan and adjacent regions.

Semisulcospira davisi sp. nov. [New Japanese name: Sazanami-kawanina] ( Figs. 4–7 ) urn:lsid:zoobank.org:act:06199C4B-4171-43E4-A455-211E220E12A4

Melania multigranosa – Pilsbry 1902: 119–120 (part); Annandale 1916: 44–46, 55, 59, pl. 3, fig. 2A–E (part).

Semisulcospira multigranosa – Kuroda 1929: 186, 189, pl. 5, figs. 34–36 (part); Burch 1968: 12, 26–29, pl. 4, figs. 1–3, pl. 5, fig. 6; Davis 1969: 255, 258, 260, 262, pl. 7, figs. 1–4, pl. 11, figs. 5–8; Watanabe 1970a: 13–30, fig. 15–2, -6, -7; Watanabe 1970b: 93–98, figs. 3–5; Oniwa and Kimura 1986: 1–2, 9–11, figs. 2–4.

Semisulcospira decipiens – Kuroda 1941: 184 (part); Kajiyama and Habe 1961: 167, figs. 4, 4a, 5, 5a; Habe 1961: 25, pl. 11, fig. 9 (part); Kuroda 1962: 86, 89; Habe 1965: 57.

Semisulcospira (Biwamelania) multigranosa – Watanabe and Nishino 1995: 1, 24, 30–34, app. pl. 1, fig. 7, app. pl. 2, figs. 20, 21; Kamiya et al. 2011: 23–34; Miura et al. 2019: 45–51, figs. 2–5.

Biwamelania multigranosa – Prozorova and Rasshepkina 2006: 130– 132, fig. B.

Material examined: Holotype. KUZ Z3680, adult shell with embryonic shells treated with sodium hypochlorite, collected from a depth of 5–6 m of Lake Biwa (35°30'00"N, 136°09'48"E), Tsukide , Nishiazaicho, Nagahama City, Shiga Prefecture, Japan, on 22 July 2020 by the first author . Paratypes. In total, 3 specimens collected with the holotype: KUZ Z3681– Z3683.

Additional materials: KUZ Z3684 collected with the holotype; KUZ Z3685, Z3686, collected from Kitafunaki, on 17 August 2017 (KUZ Z3685), and on 22 July 2020 (KUZ Z3686); KUZ Z3687, collected from Yokoehama, on 22 July 2020; KUZ Z3688, collected from Okishima, on 23 July 2020; KUZ Z3689, 3690, collected from Yoshikawa on 18 February 2018 (KUZ Z3689), and on 10 December 2019 (KUZ Z3690).

Etymology: The specific name is dedicated to Dr. George M. Davis, who greatly contributed to the systematics of Japanese Semisulcospira .

Diagnosis: Viviparous semisulcospirid. Adult shell elongated [ SH 29.5 ± 3.2 (mean ± SD); SW 9.7 ± 1.2]; 2.1 ± 0.5 BCN; 22.8 ± 2.6 curved ribs with distinct or indistinct nodes; 8.8 ± 1.0 SCN; 16.4 ± 2.2 degrees SA; 1.5 ± 0.1 ASR; 2.1 ± 0.2 WER. Embryonic shell large (SHE 4.3 ± 1.1), with ribs on surface; color in black background or beige background with brown bands.

Description of holotype: Adult shell ( Fig. 4A– C ): Female. Measurements and counts: AH 8.0 mm, AL 8.4 mm, ASR 1.5, AW 5.5 mm, BCN 2, BWL 14.1 mm, FWL 4.1 mm, PWL 6.1 mm, RN 25, SA 17.2 degrees, SCN 10, SH 32.3 mm, SW 10.1 mm, TWL 5.0 mm, WER 2.0, WN 6.00. Shell elongated. Slightly curved longitudinal ribs on whorls with indistinct spiral cords. Suture strongly undulating, sides of whorls moderately convex. Shell colored ocher in background with 1 olive color band on upper part of each whorl, 1 brown band on lower part of each whorl. Surface of shells covered with black deposits before treatment.

Operculum ( Fig. 4D ): 5.6 mm in long diameter. Nearly egg-shaped subcircular, paucispiral, comprising 3 whorls. Nucleus subcentral.

Embryonic shells ( Fig. 4E–G ): Measurements and counts: EN 7, RNE 10, SHE 4.9 mm, SWE 2.9 mm, WNE 5.00. Shell oval shape like rugby ball, with remarkable ribs. Shell colored beige background, with 1 distinct brackish brown band on upper part of each whorl and on basal part of the shell.

Radulae ( Fig. 6 ): Taenioglossa consisting of rachidian in single, lateral teeth, interior and exterior marginal teeth in double row. Rachidian roughly triangular with large central pointed denticle and 3 minor pointed triangular cusps on each side. Approximately regular triangular central denticle of rachidian about 2.5 times longer than other triangular cusps. Lateral teeth with large central pointed and tapered denticle, 3 inner and 3 outer pointed cusps. Irregular triangular central denticle of lateral teeth about 2 times longer than other triangular cusps. Interior and exterior marginal teeth similar in shape with 5–6 rounded denticles.

Reproductive organs: Male ( Fig. 7A ). Gonad consisting of testes, vas deferens, and prostate without penis. Thin narrow vas deferens running from testes and connecting to posterior end of prostate. Posterior ventral part of inflated prostate, forming deep groove, observed as U-shape in transverse section. Anterior prostate tapering toward end of prostate opening to mantle cavity.

Female ( Fig. 7B ). Long narrow oviduct, emerging from ovary, entering near seminal receptacle without protrusion. Ventral edge of spermatophore bursa with groove with curved surface forming 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 ( Table 1): Adult shell: Measurements: AH 6.4–9.8 mm [8.1 ± 0.7 (mean ± SD)], AL 6.8–10.4 mm (8.2 ± 0.8), ASR 1.3–1.7 (1.5 ± 0.1), AW 4.5–6.7 mm (5.5 ± 0.5), BCN 1–4 (2.1 ± 0.5), BWL 11.7–16.7 mm (14.1 ± 1.2), FWL 3.1–5.1 mm (4.0 ± 0.4), PWL 4.7–7.6 mm (6.0 ± 0.6), RN 16–30 (22.8 ± 2.6), SA 11.1–20.6 degrees (16.4 ± 2.2), SCN 7–10 (8.8 ± 1.0), SH 23.9–40.4 mm (29.5 ± 3.2), SW 8.3–11.3 mm (9.6 ± 0.8), TWL 3.9–6.1 mm (5.0 ± 0.5), WER 1.5–2.6 (2.1 ± 0.2), WN 3.50–8.50 (5.5 ± 1.2). Slightly to moderately curved longitudinal ribs on whorls sometimes form nodes with spiral cords. Suture slightly to strongly undulating, sides of whorls slightly to moderately convex. Shell colored ocher to olive or blackish brown in background with or without colored bands. Distinct to slightly indistinct colored bands on adult shells olive or brown in ochre background, brown in olive background. No colored band observed on shells in blackish brown background. One color band each found on upper, middle, or lower part of whorls, or on all of them.

Operculum: Nearly pear to egg-shaped subcircular, paucispiral, comprising 3 whorls. Nucleus subcentral.

Embryonic shells: Measurements: EN 2–21 (7.2 ± 4.9), SHE 2.1–7.1 mm (4.3 ± 1.1), SWE 1.6–3.5 mm (2.5 ± 0.5), RNE 9–14 (10.6 ± 1.3), WNE 2.50–6.00 (4.1 ± 0.7). Shell colored beige, olive or blackish brown in background with or without colored bands. Distinct colored bands brown to blackish brown in beige, olive background. No colored band found on shells in blackish brown background. One color band each lined on upper, middle, lower or basal part of whorls, or on all of them.

Radulae: Variation of the number and the size in cusps observed: rachidian, 1 central denticle flanked by 3–4 minor pointed cusps on each side, central denticle 2–3 times longer than marginal cusps; lateral teeth, 1 central denticle with 2–3 inner and outer cusps, central denticle 2–3 times longer than other cusps; interior and exterior marginal teeth, 5–8 cusps.

Reproductive organs: Seminal receptacles with or without several short protrusions were observed in female reproductive organs.

Distribution and ecology: The new species was found from four sites of Lake Biwa in addition to its type locality: Kitafunaki, Yokoehama, Okishima, and Yoshikawa ( Fig. 1 ). Except at Yoshikawa, the new species inhabits sandy and muddy bottom at depths of 5– 7 m. At Yoshikawa, the new species was collected from muddy bottom at the depth of 10– 15 m. Semisulcospira davisi was found with several other congeners: S. reticulata Kajiyama and Habe, 1961 , S. decipiens and S. h. yamaguchi at Tsukide, Kitafunaki and Yokoehama; S. decipiens at Okishima; and S. reticulata at Yoshikawa.

Remarks: Morphological characters of adult and embryonic shells of the new species in five localities correspond closely to those of the species examined in the previous studies as S. multigranosa ( Davis 1969; Watanabe and Nishino 1995; Table 1). Only the smallest value of SW in the present material was greater than that in Davis (1969). The reproductive organs of S. davisi are also nearly consistent with those of snails identified as S. multigranosa by Prozorova and Rasshepkina (2006). Although Prozorova and Rasshepkina (2006) observed several “long” protrusions in the female seminal receptacle, we detected several “short” protrusions only in about half of the dissected specimens.

Previous phylogenetic studies revealed that S. davisi belongs to the S. decipiens -group ( Kamiya et al. 2011; Miura et al. 2019). Although allozyme analysis failed to show robust relationships within the decipiens - group ( Kamiya et al. 2011), a phylogenomic study using a double digest restriction site associated DNA library revealed that S. davisi was closely related to S. morii Watanabe, 1984 ( Miura et al. 2019). Semisulcospira davisi is clearly distinguishable from S. morii by having more SCN and smaller SA ( Watanabe and Nishino 1995). Thus, the distinctiveness of S. davisi is unquestionably supported by both its morphological characteristics and phylogenetic position.

The examined specimens corroborate the previous finding that the new species (referred to as S. multigranosa ) can be discriminated from S. decipiens by the morphology of rachidian and lateral teeth ( Prozorova and Rasshepkina 2006), although S. davisi has similar radulae morphology with S. decipiens in the length and shape ( Watanabe 1970b). The number of rachidian cusps is exceptional in that the number in S. davisi overlaps with that in S. decipiens (one central denticle with 3–4 minor cusps on each side; Table 1).

The present study shows that S. davisi seems to predominate in deep sandy and muddy sediments with S. reticulata . Semisulcospira davisi was collected with S. reticulata from the four collection sites. Semisulcospira reticulata has large embryonic shells, and prefers the deepest area of the lake ( Davis 1969; Watanabe and Nishino 1995; Miura et al. 2019). Given that the two species share habitat preferences and large embryonic shells, the enlargement of embryonic shells may be an adaptation to deeper habitats.

Figures

Fig. 3. Lectotype of Semisulcospira multigranosa (SMF 225654). A, ventral view. B, lateral view. C, dorsal view. D, historical handwritten label. E, partly printed label. Scale bar = 10 mm.

Fig. 4. Shells of Semisulcospira davisi sp. nov. A–G, Holotype, KUZ Z3680. H–J, Specimen from Kitafunaki, KUZ Z3686. K–M, Specimen from Yokoehama, KUZ Z3687. N–P, Specimen from Okishima, KUZ Z3688. Q–S, Specimen from Yoshikawa, KUZ Z3690. A–C, H, K, N, Q, Adult shell. D, I, L, O, R, Operculum. E–G, J, M, P, S, Embryonic shell. Scale bars: 10 mm (A–D, H–I, K–L, N–O, Q–R), 2 mm (E–G, J, M, P, S). All specimens were treated with 12% sodium hypochlorite.

Fig. 6. Radula morphology of Semisulcospira davisi sp. nov. collected from type locality (KUZ Z3684). Scale bar = 100 μm.

Fig. 7. Schematic drawings indicating reproductive organs of Semisulcospira davisi sp. nov. A, Male. B, Female. Scale bar = 5 mm.

Fig. 1. Map of Lake Biwa showing five sampling localities: double circle, Tsukide (type locality of Semisulcospira davisi sp. nov.); black circles, Kitafunaki, Yokoehama, Okishima, Yoshikawa.