Sarika costata Pholyotha, 2022

Pholyotha, Arthit, Sutcharit, Chirasak, Lin, Aung & Panha, Somsak, 2022, Multigene phylogeny reveals the ribbed shell morphotypes in the land snail genus Sarika (Eupulmonata: Ariophantidae), with description of two new species from Thailand and Myanmar, Contributions to Zoology 91 (2), pp. 97-132 : 126-128

Sarika costata Pholyotha , sp. nov.

( figs 1 , 2 , 8C, D , 9C, D , 11D )

Type material examined. Holotype. CUMZ 7946 ( fig. 8C , width 10.8 mm, height 7.2 mm) . Paratypes. Same locality as holotype: CUMZ 7947 ( fig. 8D , width 10.9 mm, height 7.0 mm) .

Other material examined. Phra (Buddha) Cave , Tanintharyi Township, Tanintharyi Division, Myanmar, 11°13’46.2”N 99°10’34.3”E, CUMZ 7948 .

Type locality. Kala Island , Myeik Township , Myeik District, Tanintharyi Division, Myanmar, 12°25’54.3”N 98°29’56.3”E .

Etymology. The specific name “ costata ” is from the Latin word meaning “ribbed”, which refers to the shell surface having fine radial ribs that characterises this species within the genus Sarika .

Diagnostic characteristics. Shell medium, globosely depressed; body whorl well-rounded; shell ribbed with smooth radial ribs; aperture narrowly crescent-shaped. Animal pale grey body, black stripes behind long tentacles and five mantle edges. Genitalia with straight epiphallic caecum, cuboidal, and irregularly oblique-folded penial pilasters.

Description.Shell ( fig.8C, D ).Shell globosely depressed, medium size (width up to 12.4 mm, height up to 8.0 mm) and rather thin to slightly solid. Shell colour yellowish-brown to brownish. Whorls 6–6¼, increasing regularly. Spire much elevated; apex slightly protruding; suture impressed, slightly wider near aperture opening. Embryonic shell rather smooth; later whorl with very weak radial ridges. Body whorl large and well-rounded. Upper shell surface sculptured with regular, distinct, and smooth radial ribs, and then radial ribs disappearing below periphery. Aperture crescent-shaped, narrow, well oblique, and with simple lip. Columellar margin simple and slightly reflected near umbilicus. Umbilicus narrowly opened.

Genital organs ( fig. 9C, D ). Atrium (at) enlarged and very short. Penis (p) elongate and cylindrical. Inner surface sculptured with very finely longitudinal pilasters (pp) to nearly smooth, about one-third of penis length, covered with cuboidal pilasters in middle part, and then transformed to irregular folds arranged in oblique row about one-third of penis length. Epiphallus (e) elongate, cylindrical, and same length as penis. Epiphallic caecum (ec) straight, slightly smaller diameter than epiphallus and located at middle of epiphallus. Penial retractor muscle (prm) thin and attached at tip of epiphallic caecum. Flagellum (fl) slender, same length as epiphallus, and enlarged at the tip. Vas deferens (vd) thin tube.

Vagina (v) cylindrical and slightly shorter than penis. Dart apparatus (da) enlarged, very long, and joined to atrium at vagina and penis junction. Gametolytic sac (gs) bulbous; gametolytic duct (gd) elongate cylindrical. Free oviduct (fo) enlarged cylindrical, slightly shorter than vagina. Oviduct large lobules; prostate gland running alongside oviduct.

Radula ( fig. 11D ). Teeth arranged straight with half row formula: 1–(11–12)–50. Central tooth symmetrical tricuspid with large mesocone and small ectocones. Lateral teeth asymmetrical tricuspid with large mesocone, and small endocone and ectocone. Marginal teeth started around tooth number 11 or 12; inner teeth elongate bicuspid with lanceolate endocone and small ectocone; and outermost teeth gradually reduced in size.

External features ( fig. 2 ). Living snails with reticulated skin, dark grey eye stalks, and very pale grey body with black stripes behind long tentacles. Five well-developed mantle lobes with same colour as body. Right shell lobe moderately elongate; left shell lobe short. Dorsal lobes large and broad; anterior and posterior left dorsal lobes smaller than right dorsal lobe. Caudal fossa and caudal horn present.

Distribution ( fig. 1 ). Sarika costata sp. nov. is known from two localities, Kala Island and on the mainland at Phra Cave in Tanintharyi Region, Myanmar. Its distribution range needs further studies. We could not find this species in Thailand.

Remarks. Regardless of the genitalia and mantle characters, Sarika costata sp. nov. differs from S. theodori , S. siamensis , and S. costabilis sp. nov. by having small and smooth radial ribs, while the three latter species have relatively larger shell with nodules or dash-shaped nodules arranged on radial ribs. Moreover, this new species has five mantle edges and the inner wall of the penis is sculptured with cuboidal and folded penial pilasters, while the other three species have four mantle edges, and the inner wall of the penis is sculptured with only cuboidal penial pilasters.

Compared with the medium-sized species with costulate striation on the shell surface from Thailand and Myanmar, the shell morphology of S. costata sp. nov. is similar to Khasiella pansa ( Benson, 1856) . Khasiella pansa was described from the Irrawaddy Valley and recorded from the Mergui Archipelago ( Benson, 1856; Blanford & Godwin-Austen, 1908); however, the anatomical data of K. pansa needs further studies. In comparison, this new species has a smaller shell size, well-rounded body whorl, and narrowly crescent-shaped aperture, while K. pansa has a slightly larger, subangulate body whorl, and wider aperture ( Benson, 1856; Hanley & Theobald, 1876; Blanford & Godwin-Austen, 1908).

Figures

FIGURE 1 Geographic distribution of ribbed shell Sarika spp. based on the specimens examined herein. A) Distribution of S. theodori, S.costabilis sp.nov., and S. costata sp. nov. B) Distribution of S. siamensis. Black symbols indicate the DNA extracted specimens used in the molecular analysis; white symbols indicate shells or other preserved specimens.

FIGURE 2 Bayesian inference tree based on a 1495 bp concatenated alignment dataset of COI + 16S + 28S genes. Numbers by the nodes are the Bayesian posterior probabilities (left) and ML bootstrap values (right); shown only for the nodes supported by BI ≥ 0.95 or ML ≥ 70%. Clade A consists of the S. resplendens-S. hainesi species groups.Clade B consists of the S.siamensis species group.Images of living snails are not to scale.

FIGURE 8 Shells of Sarika spp.A, B) S. costabilis sp. nov.A) Holotype CUMZ 7943.B) Paratype CUMZ 7944.C, D) S. costata sp.nov.C) Holotype CUMZ 7946.D) Paratype CUMZ 7947.

FIGURE 9 Genitalia of Sarika spp.A, B) S. costabilis sp. nov.paratype CUMZ 7945.A) General view of the genital system.B) Internal structure of penis.C, D) S.costata sp. nov. paratype CUMZ 7947.C) General view of the genital system.D) Internal structure of penis. White arrows indicate the end of penis.

FIGURE 11 Radula of Sarika spp. A) S.theodori specimen CUMZ 7942.B) S.siamensis specimen CUMZ 7951.C) S.costabilis sp. nov. paratype CUMZ 7945. D) S. costata sp. nov. paratype CUMZ 7947.Central tooth indicated by ‘C’ and blue colour; yellow colour indicates lateral teeth in the transition to marginal teeth.