Macrochlamys lemma Pholyotha & Panha, 2018

Pholyotha, Arthit, Sutcharit, Chirasak & Panha, Somsak, 2018, The land snail genus Macrochlamys Gray, 1847 from Thailand, with descriptions of five new species (Pulmonata: Ariophantidae), Raffles Bulletin of Zoology 66, pp. 763-781 : 771-772

Macrochlamys lemma Pholyotha & Panha , new species

( Figs. 2D , 5C, D , 7A, B , 10A–C )

Material examined. Holotype ( Fig. 7A ; shell height 7.2 mm, shell width 15.9 mm, aperture height 5.0 mm, aperture width 7.6 mm) ( CUMZ 7114 ), limestone outcrops at Wat Khao Wongkot (Temple), Sanam Chaeng Village, Ban Mi District, Lopburi Province, Thailand, 15° 00′58.7″N, 100° 32′38.5″E . Paratypes: two shells ( Fig. 7B ; shell height 6.3 mm, shell width 15.0 mm, aperture height 5.6 mm, aperture width 7.0 mm, 5⅝ whorls) ( CUMZ 7115 ), 47 specimens ( CUMZ 7116 ), two shells ( NHMUK), one shell ( ZRC. MOL.13773), same data as holotype .

Etymology. The specific name, derived from Greek “ lemma ” meaning “peel, husk or sheath”, is in reference to the welldeveloped tissue casing or sheath between the vagina and dart apparatus.

Description. Shell medium-sized ( Fig. 7A, B ; shell height up to 7.6 mm; shell width up to 17.0 mm), dextral, depressed to low-conical, thin, semi-translucent, shiny and pale yellowish in colour. Shell surface smooth with thin growth lines. Embryonic shell surface smooth, small, with about 2½ whorls. Whorls 5–6, increasing regularly, with shallowly impressed suture. Spire profile from low conical to nearly flat with just a little convexity. Spire angle about 147–159°. Last whorl narrow with well-rounded periphery. Aperture crescent-shaped, obliquely open with simple lip. Columellar margin slightly reflected near umbilicus. Umbilicus narrowly open and deep.

Genital organs. Atrium (at) large and slightly long. Penis long, cylindrical in shape and distally with short and swollen penial caecum (pc) that corresponds to penial verge inside. Epiphallus (e) rather long, about two and half times of penis length, cylindrical and almost same diameter as penis. Epiphallic caecum (ec) coiled about one circle and located proximally about one-third of epiphallic length. Penial retractor muscle (prm) slightly thick. Flagellum (fl) long, about half of epiphallus length, with early stage of spermatophore formation inside. Vas deference (vd) a long tube connected between free oviduct and distal end of epiphallus ( Fig. 5C ).

Inner wall of penis proximally with oblique trapezoid penial pilasters (pp) and distally at penial caecum with long and transverse-folded surrounding penial verge (pv). Penial verge small, thick and located at distal end of penis ( Fig. 5D ).

Vagina (v) rather long, about two-thirds of penis length, cylindrically shaped with thick connective tissue encircled at vagina and dart apparatus junction (asterisk in Fig. 5C ). Dart apparatus (da) somewhat large, long cylindrical and located near proximal end of vagina above penis junction. Gametolytic sac (gs) bulbous. Gametolytic duct (gd) thick and rather short. Free oviduct (fo) long, approximately same length as penis, cylindrical in shape, and proximally encircled with thick brownish tissue about middle of its length. Oviduct (ov) are large lobules with prostate gland (pg) running alongside ( Fig. 5C ).

Radula. Each row consists of 99 teeth with formula (48- (14-13)-1-(14-15)-50). Central tooth triangular tricuspid. Lateral teeth asymmetric tricuspid with very small endocone. Elongate bicuspid marginal teeth starting from tooth number 13–15 ( Fig. 10A–C ).

External features. Animal with reticulated skin. Head, eye stalks and body dark grey, and the tail is pale orange. Caudal foss (cf) and caudal horn (ch) grey. Mantle edge (shell lobes and dorsal lobes) well developed with mix of black and dull yellow ( Fig. 2D ). Snails secrete light yellowish slime when disturbed.

Distribution and habitat. Macrochlamys lemma new species was found living in rock crevices and surfaces of limestone karst. It is currently known only from the type locality, where it is moderately abundant.

Remarks. Macrochlamys lemma new species can be diagnosed by its depressed to low-conical shell, well-rounded last whorl, wide impressed suture, and deep umbilicus. The genitalia have one circle of coiled epiphallic caecum, a short penial caecum, thick connective tissue encircling the proximal end of dart apparatus, a long epiphallus and flagellum, large and long dart apparatus located near the proximal end of the vagina above the penis and a relative short gametolytic duct and sac. The radula morphology is very similar to M. aurantia new species.

Macrochlamys lemma new species differs from M. caverna new species by its narrow umbilicus, slightly short gametolytic organ, long epiphallus and flagellum, and the dart apparatus is located above the penis connection. In comparison, M. caverna new species has a wide umbilicus, long gametolytic organ, short epiphallus and flagellum, and the dart apparatus is located opposite the penis.

The shell profile of this new species is rather variable and vary from shells with a nearly flat spire with an apex that is just a little convex to shells with a low-conical spire. The reproductive tracts of both shell forms have been examined and appear to be identical. Both have genitalia structure of long epiphallus and flagellum, short gametolytic duct and sac, thick connective tissue encircling the proximal end of the dart apparatus and a large dart apparatus locating above the penis, which are regarded as distinguishing characters of this species.

Figures

Fig. 2. Living snails of Macrochlamys spp. from Thailand. A, Macrochlamys aurantia new species, paratype (CUMZ 7103), Thong Pha Phum, Kanchanaburi, shell width about 15 mm; B, M. coleus new species, paratype (CUMZ 7106), Sai Yok, Kanchanaburi, shell width about 15 mm; C,M. caverna new species, paratype (CUMZ 7109), Tha Wung, Lopburi, shell width about 17 mm; D, M. lemma new species, paratype (CUMZ 7116), Ban Mi, Lopburi, shell width about 15 mm; E, M. tanymentula new species, paratype (CUMZ 7119), Thong Pha Phum, Kanchanaburi, shell width about 10 mm; F, M. kelantanensis (CUMZ 7125), Lam Kaen, Phang-Nga, shell width about 20 mm.

Fig. 5. Genitalia of Macrochlamys caverna new species (A, B), and M. lemma new species (C, D). A, B, Macrochlamys caverna paratype (CUMZ 7109): A, whole reproductive system; B, internal structure of penis with penial verge.C, D, Macrochlamys lemma paratype (CUMZ 7116): C, whole reproductive system; D, internal structure of penis with penial verge. Abbreviations: at, atrium; da, dart apparatus; drm, dart retractor muscle; e, epiphallus; ec, epiphallic caecum; fl, flagellum; fo, free oviduct; gd, gametolytic duct; gs, gametolytic sac; hf, head filament; ov, oviduct; p, penis; pc, penial caecum; pg, prostate gland; pp, penial pilaster; prm, penial retractor muscle; pv, penial verge; ss, sperm sac; tf, tail filament; v, vagina and vd, vas deferens. Asterisk indicates the tissue casting.

Fig. 7. Shells of Macrochlamys lemma new species (A, B), and M. tanymentula new species (C, D). A, Macrochlamys lemma holotype (CUMZ 7114); B, paratype (CUMZ 7115); C, M. tanymentula holotype (CUMZ 7117); D, paratype (CUMZ 7118).

Fig. 10. SEM images of the radula of Macrochlamys lemma new species (A–C) (paratype; CUMZ 7116), M. tanymentula new species (D–F) (paratype; CUMZ 7119), and M. kelantanensis Möllendorff, 1902 (G–I) (CUMZ 7125). Central tooth (indicated by ‘C’) with lateral teeth (A, D, G); lateral teeth with tricuspid marginal teeth transition (B, E, H); bicuspid marginal teeth (C, F, I).