Sarika costabilis 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 : 122-126

Sarika costabilis Pholyotha , sp. nov.

( figs 1 , 2 , 8A, B , 9A, B , 10 , 11C )

Type material examined. Holotype. CUMZ 7943 ( fig. 8A ; width 29.3 mm, height 16.7 mm) . Paratypes. Same locality as holotype: CUMZ 7944 ( fig. 8B , width 28.5 mm, height 16.1 mm) ,

NHMUK 0000 (two shells), and ZRC 0000 (two shells). Limestone outcrop in Cha Lae, Thong Pha Phum District, Kanchanaburi Province, Thailand, 14°56’31.1”N 98°40’10.4”E , CUMZ 7945 .

Type locality. Wat Pa Tham Sukho Prang Phe, Sangkhla Buri District, Kanchanaburi Province, Thailand 15°02’12.7”N 98°34’58.2”E .

Etymology. The specific name “ costabilis ” is from the Latin word meaning “riblike”, which refers to shell surface with transversely dashed ribs that characterises this species within the genus Sarika .

Diagnostic characteristics. Shell large, depressed; body whorl obtusely angulated; shell ribbed with nodules arranged on radial ribs. Animal dark creamy-grey body and four mantle edges. Genitalia with short and straight epiphallic caecum and cuboidal penial pilasters. Spermatophore: head filament with smooth longitudinal folds; tail filament bearing three spines near sperm sac and with branching spines on middle and terminal part.

Description.Shell ( fig.8A,B ).Shelldepressed, large size (width up to 29.3 mm, height up to 16.7 mm), and rather solid; shell colour yellowish-brown. Whorls 6–6½, increasing regularly; near aperture opening slightly sloping downwards. Spire dome-shaped; apex slightly protruding; suture impressed. Embryonic shell nearly smooth with very weak radial wrinkles. Body whorl large and obtusely angulated. Upper shell surface sculptured with distinct radial ribs, crossed by spiral lines, and with series of nodules arranged on radial ribs, and then radial ribs gradually disappearing below periphery towards umbilicus. Aperture crescent-shaped, little descending, and lip little thickened. Columellar margin simple and slightly reflected near umbilicus. Umbilicus narrowly opened.

Genital organs ( fig. 9A, B ). Atrium (at) enlarged and very short. Penis (p) elongate, cylindrical, with thin penial sheath covering near atrium. Inner surface sculptured, very finely folded to nearly smooth from atrium to one-third of penis, and then gradually transformed to cuboidal penial pilasters (pp). Epiphallus(e) cylindrical, slightly shorter than penis. Epiphallic caecum (ec) short, straight, diameter nearly equal to proximal epiphallus, and located at middle of epiphallus. Penial retractor muscle (prm) thin and attached at tip of epiphallic caecum. Flagellum (fl) very long approximately twice of epiphallus length, slender and enlarged at the tip. Vas deferens (vd) thin tube.

Vagina (v) cylindrical and slightly shorter than half of penis length. Dart apparatus (da) enlarged cylindrical and joined to atrium at vagina and penis junction. Gametolytic sac (gs) elongate bulbous (containing one spermatophore inside); gametolytic duct (gd) cylindrical and enlarged at based. Free oviduct (fo) enlarged cylindrical, approximately two times of vagina length. Oviduct large lobules; prostate gland running alongside oviduct.

Spermatophore ( fig. 10 ). Spermatophore long and needle-shaped ( fig. 10A ). Sperm sac (ss) enlarged and elongate oval. Head filament (hf) elongate with smooth longitudinal folds ( fig. 10B ). Tail filament (tf), region close to sperm sac bearing three spines: spine I very small and simple; spine II longer than spine I with bifurcating into spinules; spine III longest with complicated branching into small spinules ( fig. 10C ). Region furthest away with series of ten branching spines arranged in row located in middle (red dashed line in fig 10A ; fig. 10D ); terminal part about one-tenth of its length, composed of series of short to long delicate branching spines arranged in multiple rows, and covering terminal part of tail filament ( fig. 10E ).

Radula ( fig. 11C ). Teeth arranged in wide, straight, and with half row formula: 1–(19– 20)–70. 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 19 or 20; inner teeth elongate bicuspid with lanceolate endocone and minute ectocone; and outermost teeth gradually reduced in size.

External features ( fig. 2 ). Living snails with reticulated skin, dark grey to black eye stalks, and pale to dark creamy-grey body. Four well-developed mantle lobes with same colour as body. Right shell lobe short and left shell lobe absent. 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 costabilis sp. nov. is endemic to Thailand and, currently known from a few limestone localities in mountainous areas in Kanchanaburi Province ( fig. 1 ). We extended our survey in other karstic habitats in Thailand, but we could not find this species elsewhere.

Remarks. Among the Sarika species with a ribbed shell, the distinguishing character of S. costabilis sp. nov. is the obtusely angulated last whorl with descending aperture, genitalia with short and large epiphallic caecum and long flagellum, and spermatophore with branching spines at the middle and terminal part of tail filament. In contrast, S. siamensis has a well-rounded last whorl, aperture not descending, genitalia with long epiphallic caecum and short flagellum, and spermatophore having spines nearly the entire tail filament length. Shell morphology of S. costabilis sp. nov. is somewhat similar to S. theodori , but the latter species have long epiphallic caecum, short flagellum, and spermatophore having spines about two-thirds of the tail filament length.

Compared with other ariophantids with ribbed shells, S. costabilis sp. nov. can be distinguished from Hemiplecta textrina ( Benson, 1856) by a coarse shell sculpture and descending aperture. In contrast, the shell sculpture of H. textrina is slightly coarse and its aperture is simple ( Blanford & Godwin-Austen, 1908; Sutcharit & Panha, 2021).This new species can be separated from H. auriettae ( Tapparone-Canefri, 1889) by its small and narrow umbilicus. In contrast, the umbilicus of H. auriettae is slightly widely opened and shows all whorls ( Blanford & Godwin-Austen, 1908; Sutcharit &

Panha, 2021). However, the anatomical data of H. textrina and H. auriettae are unavailable for further comparison.

Sarika costata species group: species with

a shell surface having fine radial ribs without fine impressed spiral lines and with five mantle lobes.

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 10 Spermatophore of Sarika costabilis sp.nov.paratype CUMZ 7945.A) General view of spermatophore that was broken into two parts.B) Head filament.C–E) Tail filament.C) Three spines located close to the sperm sac.D) Region with and without branching spines.E) Branching spines on the tip region. Red dashed line indicates a series of ten branching spines near the middle length.

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.