Cryptosemelus Collinge, 1902

Pholyotha, Arthit, Sutcharit, Chirasak & Panha, Somsak, 2021, Rediscovering the dancing semislug genus Cryptosemelus Collinge, 1902 (Eupulmonata, Ariophantidae) from Thailand with description of two new species, ZooKeys 1076, pp. 43-65 : 43

Genus Cryptosemelus Collinge, 1902

Cryptosemelus Collinge, 1902: 76. Blanford and Godwin-Austen 1908: 180. Thiele 1931: 640. Zilch 1959: 326. Vaught 1989: 97. Schileyko 2003: 1332. Bank 2017: 53. Inkhavilay et al. 2019: 75.

Type species.

Cryptosemelus gracilis Collinge, 1902, by monotypy.

Description.

Shell thin, subglobose to globose, and imperforate. Shell surface smooth, polished, and with pale yellowish to olive tinge or golden amber. Whorls 3½ -4, rapidly increasing; body whorl large and rounded. Aperture oblique and crescentic with simple lip.

Animal with reticulated skin, pale grayish, brownish, blue-gray, and blackish body marked by conspicuous oblique lines running downwards and backwards. Mantle extensions well-developed and divided into two shell lobes and two dorsal lobes. Shell lobes entirely covering shell or retracted when disturbed; left and right shell lobes usually with same color as body and with or without irregular stripes; right shell lobe (rsl) broad and triangular; left shell lobe (lsl) narrow triangular and relatively small-sized. Right dorsal lobe (rdl) ovate to crescent-shaped and left dorsal lobe (ldl) undivided, larger, and crescent-shaped. Sole tripartite and lateral foot margin present. Caudal horn absent.

Genitalia with slightly short to moderately long penis, thin penial sheath, long to very long epiphallus, penial retractor muscle attached to epiphallus, and short to slightly long gametolytic duct. Epiphallic caecum, flagellum, and dart apparatus absent. Spermatophore with complex branching spines.

Radular teeth arranged in a wide U-shape with symmetrical tricuspid central tooth, asymmetrical tricuspid lateral teeth with square to oblong base-plate, and bicuspid marginal teeth with oblong plate.

Remarks.

Originally, Collinge (1902) referred this genus to the family Girasiidae , but later it was suggested to be placed under the subfamily Parmarioninae of the family Zonitidae ( Blanford and Godwin-Austen 1908). Thiele (1931) then reclassified this genus, placing it under the subfamily Helicarioninae of the family Ariophantidae . This familial classification was then widely accepted and followed by subsequent authors except with the distinct subfamilial classification in which Zilch (1959) and Vaught (1989) placed Cryptosemelus as a member of the subfamily Macrochlamydinae , while Schileyko (2003) arranged it under the subfamily Parmarioninae . Regardless of the phylogenetic study, the higher classification of Cryptosemelus is still equivocal. Therefore, in this study, we follow the most recent gastropod classification that placed Cryptosemelus under the Ostracolethinae of the Ariophantidae ( Bouchet et al. 2017).

Collinge (1902) additionally described another two monotypic semislug genera, Apoparmarion and Paraparmarion , from Peninsular Malaysia based on specimens from the Skeat Expedition. These two genera differ from the genus Cryptosemelus mainly based on the number of shell whorls and mantle extensions, shape of the caudal horn, and genital structure. The genus Apoparmarion has a very reduced shell with about two whorls, with mantle extensions rising upon the shell on all sides with the right shell lobe posteriorly large, wing-like, and covering the apex of the shell, a prominent caudal horn, and genitalia with both a flagellum and dart apparatus (Fig. 2A, B ; Collinge 1902). In contrast, Cryptosemelus has a reduced shell of about 3 to 4 whorls, with well-developed mantle extensions with the right shell lobe covering the apex and larger than the left shell lobe, a tail with no caudal horn, and genitalia without flagellum and dart apparatus. For further comparison, Paraparmarion and Cryptosemelus share a similar reduction in the number of shell whorls and the disappearance of the caudal horn, but Paraparmarion has only a right shell lobe (Fig. 2E, F ; Collinge 1902), whereas Cryptosemelus has both right and left shell lobes (Fig. 2C, D ; Collinge 1902). Unfortunately, the genitalia of the genus Paraparmarion have never been examined for comparison. A future search for additional specimens of the genus Paraparmarion is necessary for elucidating its relationship with the genus Cryptosemelus .

Figures

Figure 2. Comparison of shell and mantle lobes among the three monotypic semislugs described by Collinge (1902) A, B Apoparmarion partridgii Collinge, 1902 A original illustration and B syntype UMZC I. 66414 C, D Cryptosemelus gracilis Collinge, 1902 C original illustration and D syntype UMZC I. 66448 E, F Paraparmarion elongatus Collinge, 1902 E original illustration F syntype UMZC I. 66522. Credits: A, C, E after Collinge (1902) and B, D, F online catalogues of the UMZC, Cambridge.