Rhachistia conformalis Sutcharit & Panha, 2010

Sutcharit, Chirasak, Naggs, Fred & Panha, Somsak, 2010, A First Record Of The Family Cerastidae In Thailand, With A Description Of A New Species (Pulmonata: Orthurethra: Cerastidae), Raffles Bulletin of Zoology 58 (2), pp. 251-258 : 252-255

Rhachistia conformalis Sutcharit & Panha , new species

( Figs. 1C, D, H ; 2A, B ; 3A–D )

Type material. – Holotype CUMZ 3796 ( Fig. 1C ), 1 Sep.2007, coll. S. Panha. Measurements: shell height 19.6 mm, shell width 10.7 mm and with 6½ whorls . Paratype BMNH 20090361 (2 shells); SMF 334685 (2 shells); ZRC MOL.3008 (2 shells); CUMZ 3795 (7 shells), 3797 (1 shell; Fig. 1D ), 4086 (5 shells), 4090 (14 shells), 4095 (4 shells), 4287 (7 shells) .

Type locality. – Ban Karang , Kaeng Kracharn National Park, Phetchaburi, Peninsular Thailand (12°52'20.04"N 99° 18'20.73"E) .

Other material examined. – Pa-La-Oo Waterfall, Kaeng Kracharn National Park, Phetchaburi: CUMZ 4080 (1 shell); Tam Khiriwong, Donsak, Suratthani: CUMZ 4093 (3 shells); Wat Tam Por-ngam, Donsak, Suratthani: CUMZ 4275 (3 shells); Km. 3 (road no. 4100) to Khiriratnikhom, Suratthani: CUMZ 4652 (14 shells); Wat Sathitkhirirom, Khiriratnikhom, Suratthani: CUMZ: 4653 (2 shells); Khao Phanomwang, Kanchanadit, Suratthani CUMZ 3794 (2 shells), 4300 (5 in ethanol), 4654 (6 shells), 4915 (1 in ethanol), 4916 (2 shells); Tam Lod, Khao Nan National Park, Nakhonsrithammarat: CUMZ 4288 (4 shells), 4655 (2 in ethanol).

Etymology. – The specific name is from the Latin ‘ conformalis ’ meaning “like” or “similar”. This name refers to the new species possessing a shell superficially similar to those of the sympatric species Amphidromus glaucolarynx ( Dohrn, 1861) and Amphidromus semitessellatus ( Morlet, 1884) .

Diagnosis. – Comparison of this new species with the type species of Rhachistia demonstrates that it shares the generic characters cited above. This new species differs from R. pulcher ( Gray, 1825) and R. adumbratus ( Pfeiffer, 1855) from Sri Lanka (see Gude, 1914; Naggs & Raheem, 2000) by having a slightly thinner shell, a creamy ground colour ornamented with two rows of blackish spots on the upper periphery and two spiral bands on the lower periphery, whereas, R. pulcher has scattered blackish spots and pale spiral bands, and R. adumbratus has only blackish spiral bands on the whitish ground colour with a reddish subsutural band, pink columella area and a spiral band on the periphery.

Description. – Shell elongate conical, small, dextral, thin and fragile; apex acute with dark spot on tip. Whorls convex; suture depressed. Last whorl large, convex, yellowish-white to creamy ground colour with very fine growth lines. In the final whorl the upper periphery exhibits two rows of blackish spots, one just below the suture, the other runs approximately in middle of the last whorl; below the periphery are two brownish bands; one just below periphery, the other close to the umbilicus. Spire conical, having similar colour pattern to last whorl but slightly paler. Aperture ovate; lip simple and sharp. Parietal callus translucent. Umbilicus narrow; columella short, straight with triangular dilation.

Genitalia. – Atrium (at) rather large, long and without blackish pigments on male side ( Fig. 2A ). Penial appendix (pa) very long, about twice that of vaginal length, proximally thin, distally slightly enlarged and cylindrical. Penis (p) short, small, proximally cylindrical and distally forms swollen globular structure. Epiphallus (e) larger than vas deferens; penial flagellum (pf) very thin and short. Retractor muscle thin and split into two bundles: penial retractor muscle (pr) inserted on distal globular end of penis, and atrial retractor muscle (ar) inserted on proximal end of penial appendix. Vas deferens (vd) thin tube connected to head of epiphallus.

Vagina (v) large, long, cylindrical with blackish pigmentation along almost entire length ( Fig. 2A ). Gametolytic sac (gs) very short, bud-like. Free oviduct (fo) short; spermoviduct (so) enlarged and swollen. Albumin gland (ag) slightly enlarged, short and ligulate. Hermaphroditic duct (hd) slender and convoluted. Hermaphroditic gland (hg) forms multiple clumped alveoli embedded in digestive gland.

Pallial system. – Typical orthurethran form. Auricle (au) and ventricle (ve) located left of kidney (on right in figure). Pulmonary vein (pv) and blood vessel very distinct and well developed at anterior end near mantle collar (mc). Kidney (k) elongate, broadened at base and approximately half of lung cavity length.

Renal ureter (rnu) very thin and attached to kidney; renal fold (rtf) with very thin and transparent ridge located between kidney and rectum (r). Anus (a) adjacent to mantle collar (mc) ( Fig. 2B ).

Radula . – Teeth arranged in V-shaped rows. Each row contains about 88 (43-1-44) teeth. Central tooth monocuspid; broadly spatulate. Latero-marginal teeth (teeth number 1 to 15) bicuspid, endocone similar to central tooth; ectocone located at base of tooth and with two pointed cusps. Outermost teeth (teeth number 16 to 43 or 44) polycuspid; endocone spatulate with slightly outward oblique cusp; ectocones located laterally and progressively divided up into six pointed cusps.

Distribution. – Peninsular Thailand, ranging from Phetchaburi (the type locality) to Suratthani and Nakhonsrithammarat Provinces.

Remarks. – Superficially similar but obviously distinct from the sympatric Amphidromus semitessellatus ( Morlet, 1884) in having a smaller dextral shell, with simple lip. Although A. glaucolarynx ( Dohrn, 1861) has dimorphic shell coiling, it differs by having a thinner and smaller shell, a simple lip and a creamy shell colour. The shapes of the radula teeth and genital morphology of Amphidromus and Rhachistia are also very distinct ( Sutcharit, 2004).

Apart from our new species and R. sulphurea there are no unequivocal records of Rhachistia from the region. The shell of R. sulphurea can generally be distinguished from R. conformalis Sutcharit & Panha , new species, in that the former is thick-walled with a uniform sulphur to yellowish colour, as well as having a reddish subsutural band on the last whorl and a pink columella (Tomlin & Peile, 1930).

Rhachistia conformalis Sutcharit & Panha , new species, was found on tree trunks, branches, twigs and leaves of non-specific plants. The snails usually live higher than 2 m above ground, up to canopy height.

Figures

Fig. 1. Shell of Rhachistia sulphurea: A, lectotype NMW 1955.158.01155; B, paralectotype BMNH 1939.6.6.17. Shell of Rhachistia conformalis Sutcharit & Panha, new species: C, holotype CUMZ 3796; D, paratype CUMZ 3797. Shell of Amimopina subangulatus: E, lectotype BMNH 1986166; F, G, specimens from Jed Sao Noi Waterfall, Saraburi (CUMZ 3798, 3799). Rhachistia conformalis Sutcharit & Panha, new species: H, at type locality (shell height about 17 mm) CUMZ 3797. Amimopina subangulatus: I, at Jed Sao Noi Waterfall, Saraburi (shell height about 15 mm) CUMZ 3650.

Fig. 2. Anatomy of Rhachistia conformalis Sutcharit & Panha, new species (Paratype CUMZ 3797): A, reproductive system; B, pallial system; C, genitalia of Amimopina subangulatus from Jed Saw Noi Waterfall, Saraburi (CUMZ 3798).

Fig. 3. Radula morphology. Rhachistia conformalis Sutcharit & Panha, new species (Paratype CUMZ 3797): A, central tooth with first to third lateral teeth; B, C, lateral teeth with bicuspid marginal teeth transition; D, outermost marginal teeth. Amimopina subangulatus (CUMZ 3798): E, central tooth with first to third lateral teeth; F, G, lateral teeth with bicuspid marginal teeth transition; H, outermost marginal teeth. The numbers indicate the order of the teeth and the letter 'C’ in the images indicates the central tooth.