Cryptosemelus tigrinus 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 tigrinus Pholyotha sp. nov.

Figs 1 , 3E, F , 8 , 9 , 10C

Type material.

Holotype. CUMZ 7955 (Fig. 3E ; width 10.7 mm, height 7.6 mm). Paratypes. Same locality as holotype: CUMZ 7956 (Fig. 3F ; width 9.8 mm, height 6.8 mm), NHMUK (two shells), and ZRC (two shells). Limestone outcrops at Wat Suwan Khuha, Takua Thung District, Phang-Nga Province, Thailand (8°25'N, 98°28'E): CUMZ 7957. Limestone outcrops at Wat Tham Bang Toei, Mueang District, Phang-Nga Province, Thailand (8°27'N, 98°34'E): CUMZ 7958.

Type locality.

Limestone outcrop at Tham Phung Chang, Mueang District, Phang-Nga Province, Thailand (8°26'N, 98°30'E).

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.

Description.

Shell (Fig. 3E, F ). Shell globose, medium-sized (width up to 10.7 mm, height up to 7.6 mm), thin, smooth, polished, pale yellowish with an olive tinge. Whorls 4- 4½, rapidly increasing; last whorl large and rounded at periphery. Spire elevated; suture little impressed. Aperture oblique, diagonal, roundly ovate; peristome thin, simple. Columellar margin simple. Umbilicus imperforate.

Genital organs (Figs 8B-D , 9 ). Atrium (at) short. Penis (p) moderately long, cylindrical with thin penial sheath (ps) covering nearly half of its length; penial caecum (pc) small. Internal wall of penis: proximal part covered with very thin longitudinal folds and one thickened longitudinal fold; distal part with irregularly zigzag folds surrounding the penial verge. Penial verge (pv) elongate ovate shape and smooth surface (Fig. 8C ). Epiphallus (e1+e2) equal to penis length; e1 slightly shorter than e2 and cylindrical; proximal e2 cylindrical and smooth surface (Fig. 8B ); distal e2 cylindrical with prominently granulated surface (Fig. 8D ). 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. 8B ).

Vagina (v) long, slender, and approximately half of penis length. Gametolytic sac (gs) bulbous (Fig. 8B with spermatophore); gametolytic duct (gd) somewhat enlarged and cylindrical. Free oviduct (fo) cylindrical, about half of penis length, and encircled with thick tissue in middle (Fig. 8B ).

Spermatophore long and twisted cylindrical tube (Fig. 9 ). Head filament (hf) elongate tube with smooth surface (Fig. 9B ). Sperm sac (ss) enlarged, elongate ovate with unclear boundary between sperm sac and tail filament. Tail filament (tf) very long and enlarged tube with series of long and delicate branching spines arranged in a row, and then near the tip having multiple rows of short branching spines (Fig. 9C, D ).

Radula (Fig. 10C ). Teeth arrangement and shape similar to those of C. gracilis . Teeth with half row formula: 1-(38-39)-44 teeth. Central tooth square base-plate with symmetrical tricuspid. Inner lateral teeth square base-plate with asymmetrical tricuspid; outer lateral teeth with oblong to elongate teeth with tricuspid. Marginal teeth elongate bicuspid. Marginal teeth starting at about teeth numbers 38-39; outermost teeth shorter and smaller than inner teeth.

External appearance (Figs 1 , 8A ). Living animal with reticulated skin, pale to dark brownish body marked with prominent, oblique, dark brownish lines running downwards. Mantle extensions well-developed. Shell lobes pale yellowish-orange, painted with irregular black stripes, and enlarged to cover entire shell; right shell lobe (rsl) large (square shape in preserved specimen); left shell lobe (lsl) small (triangular shape in preserved specimen); left dorsal lobe (ldl) larger than right dorsal lobe (rdl). Foot sole divided into median and lateral planes. Caudal horn absent.

Etymology.

The specific name is a Latin word " Cryptosemelus 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.

Remarks.

Cryptosemelus tigrinus sp. nov. differs from C. gracilis and C. betarmon sp. nov. in having pale yellow-orange banded shell lobes and a well-developed penial verge, whereas C. gracilis and C. betarmon sp. nov. have monochrome shell lobes and do not have a penial verge.

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 8. Cryptosemelus tigrinus sp. nov. paratype CUMZ 7956 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.

Figure 9. Spermatophore of Cryptosemelus tigrinus sp. nov. paratype CUMZ 7956 A general view of the spermatophore B-D SEM images B head filament without spine C branching spines on the unclear boundary between sperm sac and tail filament, and D tail filament showing branching spines; inset showing cross section of tail filament. Red arrow indicates position of cross section of tail filament.

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.