Macrochlamys coleus 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 : 769

Macrochlamys coleus Pholyotha & Panha , new species

( Figs. 2B , 3C, D , 4F–I , 6D–F )

Material examined. Holotype ( Fig. 3C ; shell height 6.6 mm, shell width 13.0 mm, aperture height 5.0 mm, aperture width 6.2 mm, 5½ whorls) ( CUMZ 7104 ), limestone outcrops at Wat Sunantha Wanaram (Temple), Sai Yok District, Kanchanaburi Province, Thailand, 14° 32′01.6″N, 98° 50′13.8″E . Paratypes: one shell ( Fig. 3D ; shell height 6.0 mm, shell width 12.3 mm, aperture height 4.5 mm, aperture width 6.1 mm, 5¼ whorls) ( CUMZ 7105 ), 10 specimens ( CUMZ 7106 ), same data as holotype .

Etymology. The specific epithet “ coleus ”, from the Latin word meaning “sheath”, refers to the well-developed tissue covering between the vagina and dart apparatus.

Description. Shell medium-sized ( Fig. 3C, D ; shell height up to 6.6 mm; shell width up to 13.0 mm), dextral, depressed, slightly thick, translucent brown in colour. Shell surface nearly smooth, with very fine growth lines. Embryonic shell surface smooth, with about 2½ whorls. Whorls 5–6, increasing regularly. Suture wide and shallow, channel-shaped. Spire depressed, apex slightly raised with spire angle of about 148–152°. Last whorl well rounded. Aperture crescent ovoid shaped, obliquely open, with simple lip. Columellar margin little developed and slightly reflected near umbilicus. Umbilicus narrowly open.

Genital organs. Atrium (at) short. Penis prolonged, cylindrical-shaped with rounded bulge corresponding to penial verge. Penial caecum (pc) slightly prolonged. Epiphallus (e) slender tube about two times longer than penis. Epiphallic caecum (ec) coiled about one circle, located at middle of epiphallus and attached with thick penial retractor muscle (prm). Flagellum (fl) short, cylindrical shaped and stretched around half of epiphallus length. Vas deference (vd) a thin tube connected between distal end of epiphallus and free oviduct ( Fig. 4F ).

Inner penial wall supported proximally with small and irregular wrinkled penial pilasters (pp), distally with thin longitudinal and wrinkled folds. Penial verge (pv) very small and short, situated at distal end of penis ( Fig. 4G ).

Vagina (v) slightly long, almost same length as penis and cylindrical. Dart apparatus (da) long, enlarged cylindrical shape, located at proximal end of vagina, with thick connective tissue encircled at proximal end (asterisk in Fig. 4F ). Gametolytic sac (gs) elongate and bulbous. Gametolytic duct (gd) long and cylindrical (one spermatophore in Fig. 4F ). Free oviduct (fo) short, about similar length to flagellum, proximal end encircled with brownish tissue. Oviduct (ov) large lobules with prostate gland (pg) running alongside ( Fig. 4F ).

Spermatophore long, needle-shaped and translucent ( Fig. 4H ). Head filament (hf) short, gradually tapering to a point ( Fig. 4I ). Sperm sac (ss) enlarged, cylindrical capsule-shaped with sperm mass. Tail filament (tf) long, curved with many spines. Region close to sperm sac bear a single trichotomous spine divided into three pointed tips. Middle region with a row of five, long curved spines. Region furthest away from sperm sac contains small cluster of short spines ( Fig. 4H ).

Radula. Each row contains about 92 teeth with formula (45- (12-11)-1-(11-12)-46). Central tooth symmetric tricuspid. Lateral teeth asymmetric tricuspid. Marginal teeth obliquely bicuspid starting from tooth number 11–12 ( Fig. 6D–F ).

External features. Animal with reticulated skin. Head, eye stalks and body dark grey, and tail orange ( Fig. 2B ). Caudal foss (cf) long and narrow. Caudal horn (ch) large and dark grey in colour. Mantle edge (shell lobes and dorsal lobes) well developed, orange with black pigmented spots spread all over. Shell lobes and dorsal lobes similar in morphology to M. aurantia new species. Snails secrete light orange slime when disturbed.

Distribution and habitat. This new species is currently known only from the type locality, an area of limestone outcrops with a relatively low population density. The snails were mostly found on decaying leaf litter or sometimes climbing on limestone walls.

Remarks. Macrochlamys coleus new species is distinguished by a depressed shell, dark brown in colour, and rather shallowly channelled suture. The genitalia have one circle of coiled epiphallic caecum, and dart apparatus with a thick connective tissue encircling the proximal end. Its spermatophore has a single trichotomously branched spine at the proximal end, five long spines in the middle, and a cluster of small spines at the distal end of tail filaments. Its radula morphology is very similar to M. aurantia .

This new species is close to M. aurantia new species, but can be differentiated by its small last whorl and shallow channelshaped suture. Anatomically, the genitalia have a short flagellum and well-developed connective tissue surrounding the proximal end of the dart apparatus; characters missing in M. aurantia new species. In addition, the spermatophore of this new species has a trichotomous spine on the tail filament close to the sperm sac and a row of long and curved spines on the middle part of the tail filament, while M. aurantia new species has one dichotomous spine and two simple spines on the tail filament close to the sperm sac. This new species differs from M. hypoleuca ( Blanford, 1865) and M. nebulosa ( Blanford, 1865) from Myanmar by its depressed shell with a broad last whorl and dark brown shell colour. In comparison, M. hypoleuca has a two-toned shell that is brown above the periphery and white below, while M. nebulosa has a conoidal, depressed, shell that is bluntly angulated at the periphery.

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. 3. Shells of Macrochlamys aurantia new species (A, B), M. coleus new species (C, D), and M. caverna new species (E, F). A, Macrochlamys aurantia holotype (CUMZ 7101); B, paratype (CUMZ 7102); C, M. coleus holotype (CUMZ 7104); D, paratype (CUMZ 7105); E, M. caverna holotype (CUMZ 7107); F, paratype (CUMZ 7108).

Fig. 4. Genitalia of Macrochlamys aurantia new species (A–E), and M. coleus new species (F–I). A–E, Macrochlamys aurantia paratype (CUMZ 7103): A, whole reproductive system; B, internal structure of penis with penial verge; C, spermatophore; D, detail of spines between sperm sac and tail filament; E, spines on the end of tail filament. F–I, Macrochlamys coleus paratype (CUMZ 7106): F, whole reproductive system; G, internal structure of penis with penial verge; H, spermatophore; I, head filament. 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. 6. SEM images of the radula of Macrochlamys aurantia new species (A–C) (paratype; CUMZ 7103), M. coleus new species (D–F) (paratype; CUMZ 7106), and M. caverna new species (G–I) (paratype; CUMZ 7109). 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).