Cryptosemelus betarmon Pholyotha, 2021

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

Cryptosemelus betarmon Pholyotha sp. nov.

Figs 1 , 3C, D , 6 , 7 , 10B

Type material.

Holotype. CUMZ 7959 (Fig. 3C , width 7.4 mm, height 4.1 mm).

Paratypes. Same locality as holotype: CUMZ 7960 (Fig. 3D , width 7.3 mm, height 4.1 mm), NHMUK (two shells), and ZRC (two shells). Limestone outcrops at Sam Roi Yot District, Prachuap Khiri Khan Province, Thailand (12°14'N, 99°55'E): CUMZ 7961.

Type locality.

Limestone outcrop at Wat Bang Pu, Sam Roi Yot District, Prachuap Khiri Khan Province, Thailand (12°12'N, 100°00'E).

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.

Description.

Shell (Fig. 3C, D ). Shell depressedly subglobose, small size (width up to 7.4 mm, height up to 4.1 mm), thin, smooth, polished, pale yellowish with olive tinge. Whorls 3½ -4, rapidly increasing; body whorl large and well-rounded at periphery. Spire slightly elevated; suture little impressed. Aperture oblique, diagonal, roundly ovate; peristome thin, simple. Columellar margin simple. Umbilicus imperforate.

Genital organs (Figs 6B-D , 7 ). Atrium (at) short. Penis (p) somewhat short, cylindrical, and with thin penial sheath (ps) covering most of the penis; penial caecum (pc) enlarged and bulbous. Internal sculpture of proximal penis covered by nearly smooth surface and with thickened papilla (protruded tissue); and in penial caecum covered by irregularly folds (Fig. 6C ). Epiphallus (e1+e2) approximately four times total penis length; e1 shorter than e2 and cylindrical; proximal e2 enlarged and with undulated surface (Fig. 6D ) and then gradually reduced diameter to distal end (Fig. 6B ). Penial retractor muscle (prm) thick, enlarged at base and attached at junction between e1 and e2. Vas deferens (vd) thin tube connected between distal epiphallus and free oviduct (Fig. 6B ).

Vagina (v) cylindrical, and slightly shorter than a half of penis length. Gametolytic sac (gs) bulbous (Fig. 6B with spermatophore); gametolytic duct (gd) cylindrical, enlarged at base, and then gradually reduced in diameter to gametolytic sac. Free oviduct (fo) long, cylindrical, approximately two times total penis length, and encircled with thick tissue in middle (Fig. 6B ).

Spermatophore incomplete (sperm sac and tail filament missing). Head filament (hf) with nine branching spines arranged in a single row along the head filament section (Fig. 7 ).

Radula (Fig. 10B ). Teeth arrangement and shape similar to those of C. gracilis . Teeth with half row formula: 1-(27-28)-37 teeth. Central tooth square base-plate with symmetrical tricuspid. Inner lateral teeth square base-plate with asymmetrical tricuspid; outer lateral teeth oblong to elongate tricuspid. Marginal teeth elongate bicuspid. Marginal teeth starting at about teeth numbers 27-28; outermost teeth shorter and smaller than inner teeth.

External appearance (Figs 1 , 6A ). Living animal with reticulated skin, pale to dark grayish body marked by prominent, oblique, pale brownish lines running downwards. Four mantle extensions well-developed and same color as body. Shell lobes enlarged to cover almost entire shell; right shell lobe (rsl) larger than left shell lobe (lsl); right dorsal lobe (rdl) smaller than left dorsal lobe (ldl). Foot sole divided into median and lateral planes. Caudal horn absent.

Etymology.

The specific name " Cryptosemelus 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.

Remarks.

This new species is a small-sized Cryptosemelus species which has a subglobose and pale yellowish shell with an olive tinge, and genitalia with a penial caecum and without an epiphallic diverticulum. Compared to the type species, this species has a globose and pale golden amber shell, genitalia with two small diverticula on the epiphallus, and no penial caecum.

Figures

Figure 1. 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.

Figure 3. Shells A, B Cryptosemelus gracilis specimen CUMZ 7954 C, D C. betarmon sp. nov. C holotype CUMZ 7959, and D paratype CUMZ 7960 E, F C. tigrinus sp. nov. E holotype CUMZ 7955, and F paratype CUMZ 7956.

Figure 6. Cryptosemelus betarmon sp. nov. paratype CUMZ 7960 A both sides of animal showing four lobes of mantle B-D genitalia B general view of the genital system C internal structure of the penis, and D external structure of epiphallus (e 2). White arrow indicates the end of the penis. Yellow arrow indicates the protruded tissue inside the penis near the atrium.

Figure 7. Spermatophore of Cryptosemelus betarmon sp. nov. paratype CUMZ 7960 A General view of head filament and B SEM images of head filament showing branching spines.

Figure 10. Representative SEM images of the radula A Cryptosemelus gracilis specimen CUMZ 7954 B C. betarmon sp. nov. paratype CUMZ 7960, and C C. tigrinus sp. nov. paratype CUMZ 7956. Central tooth indicated by ' C'; blue color indicates central tooth row; yellow color indicates the transition of outer lateral to marginal teeth.