Dicharax Kobelt & Moellendorff , 1900

Pall-Gergely, Barna, Sajan, Sheikh, Tripathy, Basudev, Meng, Kaibaryer, Asami, Takahiro & Ablett, Jonathan D., 2020, Genus-level revision of the Alycaeidae (Gastropoda, Cyclophoroidea), with an annotated species catalogue, ZooKeys 981, pp. 1-220 : 1

Genus Dicharax Kobelt & Moellendorff, 1900

Charax Benson, 1859: 177.

Dicharax Kobelt & Möllendorff, 1900: 186 (new replacement name for Charax Benson, 1859, non Charax Scopoli, 1777 [ Pisces]).

Chamalycaeus (Dicharax) - Thiele 1929: 108; Wenz, 1938: 478; Egorov 2013: 37.

Chamalycaeus (Sigmacharax) Kuroda, 1943: 8.

Chamalycaeus (Cipangocharax) Kuroda, 1943: 11.

Chamalycaeus (Awalycaeus) Kuroda, 1951: 73-74.

Chamalycaeus (Awalycaeus) - Egorov 2013: 35-36.

Chamalycaeus (Cipangocharax) - Egorov 2013: 36.

Chamalycaeus (Sigmacharax) - Egorov 2013: 37-38.

Dicharax - Páll-Gergely et al. 2017: 10; Páll-Gergely and Asami 2017: 14 ( Awalycaeus , Cipangocharax and Sigmacharax are synonyms).

Type species.

Alycaeus hebes Benson, 1857 (Fig. 13A ), SD Gude (1921: 236); Awalycaeus abei Kuroda, 1951 (Fig. 13B ), by monotypy ( Awalycaeus ); Alycaeus biexcisus Pilsbry, 1902 (Fig. 13C ), by monotypy ( Cipangocharax ); Chamalycaeus (Sigmacharax) itonis Kuroda, 1943 (Fig. 13D ), by monotypy ( Sigmacharax ).

Diagnosis.

Shell very small to very large (D: 1-11 mm), in most cases the spire low (dorsal side flattened), spire rarely elevated (shell globular); protoconch low in nearly all species, smooth or finely pitted, not spirally striated; R1 usually glossy, sometimes ribbed (ribs can vary from weak to strong), but spiral lines almost always absent; R2 of variable length, typically with prominent ribs which are bent in an anterior direction, but many species have smooth R2 or straight ribs; R3 well developed, often with blunt or sharp swelling, in some taxa reduced (mostly ' Awalycaeus '). Operculum thin or with various outer funnel-like structure resulting from modifications of the multispiral lamina. Central tooth typical for the family: 5-7 cusps, broad, central cusp pointed.

Differential diagnosis.

This genus can be recognised by the absence of spiral striation on the entire shell (protoconch and teleoconch). Very few species with spiral striation are classified in this genus.

Distribution.

Dicharax inhabits a large geographic area from the southeastern Himalayan region to Japan, and through the Malay Peninsula to the southern arc of the Malay Archipelago up to Sumatra and Java. There are also isolated occurrences in the Western Ghats of India and in the southwestern Himalaya (see Fig. 14 ).

Remarks.

Cipangocharax , introduced as the subgenus of Chamalycaeus , was described for a single species, Alycaeus biexcisus . The diagnosis of Cipangocharax was in fact the abbreviated description of Alycaeus biexcisus . Kuroda (1943) indicated some features in italics, emphasising the importance of these characters to distinguish Cipangocharax from other members of Chamalycaeus . These characters were the extraordinary thickness of the operculum, and the closely coiled outer belt on the outer surface of the operculum. The Japanese Chamalycaeus species described since Kuroda’s (1943) paper showed that there are transitional character states between the thick and belted operculum of A. biexcisus and the thin and unbelted opercula of most Japanese Chamalycaeus species (e.g., Minato 1993). For example, the operculum of Cipangocharax kiuchii is relatively slim, whereas that of " Chamalycaeus " miyazakii is exceptionally thickened. Consequently, the thickness of the operculum is not a distinguishing feature between Cipangocharax and other Japanese species assigned to Chamalycaeus . The outer opercular belt is missing in C. placenovitas (a species being otherwise very similar to A. biexcisus ), therefore this character is also not stable within the genus. Moreover, the outer belt is known to be present and absent within the same species, or even population (see under Chamalycaeus nipponensis and Dicharax simplicilabris , see Páll-Gergely et al. 2017). The other distinctive character mentioned by Kuroda (1943) is the sinuated columellar margin. This region is not sinuated either in C. placenovitas , or in C. okamurai . Therefore, this character is also not stable within the genus. Moreover, Japanese Chamalycaeus species with unstriated protoconchs show an extraordinary diversity in terms of the formation of the aperture ( C. expanstoma , C. okamurai , C. yanoshigehumii ), indicating that the morphological variation is very high between species. Consequently, among the Japanese species with unstriated protoconch, it would not be legitimate to classify certain species into separate (sub)genera from the others. Furthermore, the species classified into the genus Sigmacharax also do not differ considerably from the rest of Japanese species with a smooth protoconch. Therefore, based on the absence of the spiral striation on the entire shell, these species are classified in the genus Dicharax . The overlapping ribs near the tube (Fig. 15 ) may a synapomorphic character of Japanese and Korean Dicharax , but this character was also found in the Chinese species D. alticola ( Páll-Gergely et al. 2017), which is, due to the geographic distance, probably only distantly related. The morphological variation within the genus Dicharax (especially in northeastern India and in the Malay Archipelago) is so large, that at the current time we do not find it meaningful to separate the Japanese and Korean species into a separate subgenus within Dicharax .

Awalycaeus is a peculiar group of alycaeids due to the reduced (short, un-swollen) R3. However, in Awalycaeus yanoshokoae there is a moderately developed R3, which can be interpreted as an intermediate form between Awalycaeus and the rest of Japanese alycaeids which have a smooth protoconch. Given that the other shell characters (absence of spiral striation, merged R2 ribs) are similar to the other Japanese species, we also treat Awalycaeus as a synonym of Dicharax .

Such 'over spitting’ of generic taxa inhabiting Japan has also been documented in the pulmonate family Clausiliidae , which is a character-rich family such as the Alycaeidae ( Páll-Gergely et al. 2019). Nordsieck (1998) stated that the Japanese clausiliid genera and subgenera correspond only to subgenera and species groups of Western Palaearctic clausiliids. This claim was confirmed by recent molecular phylogeny ( Motochin et al. 2017).

For the sake of simplicity, this genus is divided into three sections: typical (with curved R2 ribs), atypical (without the typical R2 sculpture), and those species from Japanese and Korean localities (including species formerly classified into Awalycaeus , Cipangocharax , and Sigmacharax ).

Figures

Figure 13. Type species of alycaeid genus-group taxa A Dicharax hebes (Benson, 1857) (SMF 109244; type species of Dicharax) B D. (?) abei (Kuroda, 1951) (NSMT 50125; type species of Awalycaeus) C D. (?) biexcisus (Pilsbry, 1902) (NSMT 263; type species of Cipangocharax) D D. (?) itonis (Kuroda, 1943) (NSMT 78866; type species of Sigmacharax). Close-up images of the aperture are not to scale. All photographs: Barna Pall-Gergely.

Figure 14. Distribution of Dicharax Kobelt & Moellendorff, 1900.

Figure 15. R 2 ribs of Japanese Dicharax Kobelt & Moellendorff, 1900 species A, B Dicharax (?) abei (Kuroda, 1951), NSMT 50125 C, D Dicharax (?) biexcisus (Pilsbry, 1902), NSMT 263 E, F Dicharax (?) itonis (Kuroda, 1943), NSMT 78866. All images: Barna Pall-Gergely.