Sinotaia quadrata ( Benson, 1842 )

Hsu, Chia-Hsin, Osipova, Diana & Lin, Chien-Hsiang, 2025, Fossil freshwater mollusks from the Early Pleistocene (Calabrian) of northern Taiwan, Geodiversitas 47 (20), pp. 721-737 : 724-726

Sinotaia quadrata ( Benson, 1842)

( Figs 4, 5)

Paludina quadrata Benson, 1842: 487 .

Paludina purificata Heude, 1890: 176 , pl. 40, fig. 4, 4a.

Viviparus ( chinensis var?) formosensis Kobelt, 1909: 413 , pl. 77, figs 6-7.

Vivipara quadrata – Odhner 1930: 27.

Vivipara cf. lecythoides – Hsu 1935: 32, pl. 3, figs 2a-b, 3-5.

Vivipara dispiralis – Hsu 1935: 33, pl. 3, figs 6a-b, 7a-b, pl. 4, fig. 10.

† Bithinia viviparoides Hsu, 1936: 32 , pl. 2, figs 19a-b, 20.

Viviparus quadratus turritus Yen, 1939: 36 , pl. 3, fig. 8.

Viviparus quadratus limnophilus – Yen 1939: 192; 1943: 284.

Viviparus quadratus – Kuroda 1941: 82. — Yen 1941: 191; 1943: 284.

Bellamya purificata – Yen 1943: 126.

Sinotaia quadrata – Pace 1973: 30, pl. 5, fig. 2.

(For an extensive synonymy list of S. quadrata in East Asian, refer to Ye 2020)

MATERIAL EXAMINED. — Taiwan • 37 specimens; Shuiniukeng (= Water Buffalo Valley ), New Taipei City; Tananwan Formation; Early Pleistocene, Calabrian; ASIZF0100893 - ASIZF0100912 , ASIZF0100923 - ASIZF0100939 .

DESCRIPTION

Shell turbiniform, elongate subconical, appears thin, but not fragile. Medium to large in size, with HSh and WSh of adult shell ranging from 25-40 mm and 15-25 mm, respectively. HBW of adult shell about 70% of HSh. HA longer than WA. Shell solid, whorls profile rounded with distinct periphery, sutures impressed but shallow on early whorls, and deep suture of the body whorl. Surface shiny with weak growth lines, with 1-3 loose spiral keels (better visible on the last whorl), not evident in some specimens. Spire rather short, rounded, consists of 4-5 whorls that enlarged slowly; ratio of 1:1.5 to body whorl. Aperture subovate, broad, and prosocline, well angled posteriorly. Umbilicus small and narrow.Subadult shells ( Fig. 4M) with pronounced 2-3 spiral keels that become less prominent with age. Juvenile shell ( Fig.5 B-E) conical, turbiniform, early protoconch of 3 whorls with evident 2-3 ridges.

REMARKS Viviparid snails exhibit modest sexual dimorphism within species, due to their ovoviviparous reproductive strategy ( Minton & Wang 2011). Additionally, shell shape variation, partly influenced by environmental factors, sometimes leads to slight morphological differences between closely related species ( Chiu et al. 2002). For instance, Sinotaia quadrata histrica (Gould, 1859) inhabiting lagoonal environments develops thicker, more elongated shells with narrower apertures comparing to those found outside the lagoon ( Kagawa et al. 2019). A similar case involves the often co-occurring invasive Cipangopaludina chinensis (Gray, 1833) and C. japonica (Martens, 1861) in the United States, which are morphologically indistinguishable, likely due to their shared habitats ( Van Bocxlaer & Strong 2016). These phenotypic variations make species identification in viviparids challenging if relying solely on shell morphology. Moreover, the taxonomic uncertainty surrounding viviparid species has persisted since the 19th century and remains unresolved ( Van Bocxlaer & Strong 2019; Ye 2020; Stelbrink et al. 2020).

In this study, the juvenile specimens played a crucial role in identifying S. quadrata . Juvenile shells from the Tananwan Formation closely resemble the outline and microsculpture of extant juvenile shells of S. quadrata ( Fig. S1A, B). Compared to C. chinensis juveniles ( Fig. S1C), the Tananwan juveniles have a less angular outline and the widest point positioned closer to the anterior.They also differ from C. japonica juveniles ( Fig.S1D) in having a larger spire whorl angle, resulting in a distinct outline. While typical adult shells of these species differ significantly from our specimens ( Fig. S1 E-H), the Tananwan specimens share similarity with some of the morphotypes of those species ( Fig. S1 I-L), though the Tananwan adults are smaller than C. chinensis and C. japonica . Thus, based on both juvenile and adult shell morphology, our specimens are most likely belong to S. quadrata . This species has a wide distribution in East Asia, with records from China ( Yen 1943), Korea ( Lee 2009), and Japan ( Hirano et al. 2015; Saito & Kagawa 2020). In Taiwan, this species was first reported as Viviparus angularis (Müller, 1774) , followed by more recent studies ( Pace 1973; Chiu et al. 2002). Chen (2011) summarized at least 12 varieties of shell morphotypes of S. quadrata across Taiwan. In addition, the subspecies S. quadrata heudei ( Dautzenberg & Fischer 1905) is distinguished by its smaller shell with three well-defined spiral keels ( Chen 2011). However,this subspecies has been recognized as synonym of the S. quadrata ( Qian et al. 2014; Ye 2020).

Fossil occurrences of S. quadrata are known from Pleistocene deposits in Asia ( Taiwan Malacofauna Database 2013; Ye et al. 2020). Yen (1943) referred to this species as Viviparus quadratus Benson, 1843 from the Para-loess Formation (possibly Late Pleistocene) in the Yangtze Valley. This species has also been identified in the Upper Pleistocene deposits in Maping (Liuchow), Kwangsi, and Maoshan, Chuyung, Kiangsu ( Yen 1943), as well as from Toning and Hainan ( Odhner 1930). Yen (1943) synonymized † Bithinia viviparoides Hsu, 1936 from the Siashu Formation (Late Pleistocene), Nanking, China ( Hsu 1936), with S. quadrata . Additionally, Viviparus quadratus limnophilus Mabille, 1886 , which Yen (1943) synonymized with Vivipara dispiralis Heude 1890 , was recorded from the post-Pleistocene period in Kweilin, Kwangsi ( Hsu 1935).