Monday, December 13, 2021

[Mollusca • 2021] Cryptosemelus betarmon & C. tigrinus • Rediscovering the Dancing Semislug Genus Cryptosemelus Collinge, 1902 (Eupulmonata, Ariophantidae) from Thailand with Description of Two New Species


Cryptosemelus betarmon Pholyotha & C. tigrinus Pholyotha

in Pholyotha, Sutcharit & Panha, 2021  
All not to scale. 

Knowledge of Thai semislugs remains scarce, especially the dancing semislug genus Cryptosemelus. Prior to the present study, only a single species has been recognized with little available information. To address this knowledge gap, we surveyed for semislugs in western and southern Thailand, which yielded three species belonging to the genus Cryptosemelus. The little-known type species C. gracilis is redescribed herein, including a comparison with the type specimens. Two additional species, C. betarmon sp. nov. and C. tigrinus sp. nov., are described as new to science. All three species are characterized by differences in their genital anatomy, especially with respect to anatomical details of the penis, epiphallus, and spermatophore. In addition, C. tigrinus sp. nov. differs from C. gracilis and C. betarmon sp. nov. in the mantle color pattern.

Keywords: Diversity, endemic, land snail, limestone, Malay Peninsula, systematics, taxonomy

Superfamily Helicarionoidea Bourguignat, 1877

Family Ariophantidae Godwin-Austen, 1883
Subfamily Ostracolethinae Simroth, 1901

Genus Cryptosemelus Collinge, 1902 
Type species: Cryptosemelus gracilis Collinge, 1902, by monotypy.

 Cryptosemelus gracilis Collinge, 1902

Diagnosis: Shell globose and pale golden amber. Animal with blue-gray body. Genitalia with large vagina and elongated epiphallus with two small diverticula. Inner sculpture of penis with a small papilla near atrium. Spermatophore with a head filament of several spines and long tail filament with a cluster of small spines at the tip.

Distribution, habitat, and behavior observations: Cryptosemelus gracilis can be found in Satun, Yala, Songkhla, and Pattani Provinces in southern Thailand (Fig. 1). We searched after rain and found the semislug populations normally hiding under the slope of rocks or the tree trunks, and sometimes climbing on the rocks or low branches of plants. When the semislug are disturbed, they escape by quickly flipping and wagging their tail, and then falling on the floor. Information on its natural predators and parasites remains scarce, but the carnivorous slug genus Atopos and streptaxid snails were found sympatrically with this semislug.

Geographic distribution and living animals of Cryptosemelus gracilis, C. betarmon sp. nov., and C. tigrinus sp. nov. based on the specimens examined herein.
All not to scale. 
Black symbols indicate type locality and white symbols indicate other localities.
 Cryptosemelus betarmon Pholyotha, sp. nov.

Diagnosis: Shell depressedly subglobose and pale yellowish. Animal with grayish body. Genitalia with penial caecum, small vagina, and elongated epiphallus. Inner sculpture of penis with papilla and penial caecum. Spermatophore with a row of branching spines.

Etymology: The specific name “betarmon” is from the Greek word meaning a dancer and refers to the fidgety movements or dance-like movements of living semislugs found in the field after being disturbed.

Distribution, habitat, and behavior observations: Cryptosemelus betarmon sp. nov. is restricted to the limestone outcrops in Prachuap Khiri Khan Province, Thailand (Fig. 1). During the rainy season, but with low precipitation, the semislugs were found inactive under the decaying leaf litter or sometimes inside the hole of decaying wood. This semislug species also moved quickly as well as quickly flipping and wagging its tail to escape after being disturbed. The data on its natural enemies are unknown, but the carnivorous snail, Haploptychius sp. (Streptaxidae), was found at a high abundance in the type locality.

 Cryptosemelus tigrinus Pholyotha, sp. nov.
Diagnosis: Shell globose, pale yellowish. Animal with brownish body, shell lobes pale yellowish-orange and flanked with irregular black bands. Genitalia with long penis and vagina and epiphallus with granulated surface near vas deferens; penial caecum and penial verge present. Inner sculpture of penis: proximal part with one thickened longitudinal fold; distal part with irregular folds. Spermatophore with smooth head filament and long tail filament with several delicate, branching spines.

Etymology: The specific name is a Latin word “tigrinus”, a noun in apposition referring to the dark stripes on shell lobes, which is similar to the color pattern of the tiger.

Distribution, habitat, and behavior observations: Cryptosemelus tigrinus sp. nov. can be found on the limestone hills in Phang-Nga Province (Fig. 1). This new semislug species has a high activity level, and is abundant in moist weather conditions after rain. They were seen hanging, crawling, or slowly climbing on the wet surface of the limestone rocks, tree trunks, and limestone shrubs. This new species also has an escape behavior similar to the other congeners. Its predators are unknown, but the carnivorous slug Atopos sp. (Rathuisiidae) and Discartemon sp. (Streptaxidae) were sympatric with the new species.

 Arthit Pholyotha, Chirasak Sutcharit and Somsak Panha. 2021. Rediscovering the Dancing Semislug Genus Cryptosemelus Collinge, 1902 (Eupulmonata, Ariophantidae) from Thailand with Description of Two New Species. ZooKeys. 1076: 43-65.  DOI: 10.3897/zookeys.1076.75576