Arinia (Notharinia) micro Marzuki & Foon, 2016

Marzuki, Mohammad Effendi bin & Foon, Junn Kitt, 2016, A new land snail, Arinia (Notharinia) micro (Caenogastropoda: Cyclophoroidea: Diplommatinidae), from a limestone karst in Perak, Peninsular Malaysia, Raffles Bulletin of Zoology 64, pp. 313-318 : 314-316

Arinia (Notharinia) micro Marzuki & Foon , new species

Figs. 1 , 2

Type material. Holotype (BOR/MOL 6227) and paratypes (BOR/MOL 6228/2; ME0000883/>10): Malaysia, Perak, central Gunung [=Mountain] Rapat, limestone outcrops in Kek Lok Tong , approximately 6.9 kilometres south of Ipoh , 4°33’13.45”N, 101°7’50.34”E, coll. M.E. Marzuki, 26 May 2011.

Diagnosis. Shell minute, cylindrical, translucent. Whorls 4.5. All whorls except the protoconch sculptured with dense, prominent, thin radial ribs. Spiral ridges very fine, evenly spaced and distinct. Last part of body whorl detached, peristome not touching the ultimate whorl. Umbilicus deep. Peristome simple, reflected at the parietal area but not the palatal and basal areas.

Description. Shell minute, delicate, dextral. Color dull white, translucent. Suture deeply impressed. Whorls 4.5, convex. Apical whorl depressed conical, width of the antepenultimate, penultimate and ultimate whorl consistent, thus shell appears cylindrical. Periphery rounded for all whorls. Apex somewhat sunken, slightly depressed and concave. Protoconch rounded, smooth, distinctly oblique at 25 degrees to the teleoconch. Teleoconch commences with abruptly sculptured orthoclinic radial ribs. Radial sculpture is present on all whorls except the protoconch and is characterised by dense, straight, pronounced, sharp thin ribs. Radial ribs slightly sinuous particularly on apical and ultimate whorls. Radial rib density varies ontogenically, ribs more loosely spaced at the start of the teleoconch, denser at the apical and antepenultimate whorls (10 ribs per 0.1 mm), less dense at the penultimate and ultimate whorls (6 ribs per 0.1 mm) and very dense towards the terminal of the ultimate whorl (7 ribs in 0.04 mm before the aperture, equivalent to 17.5 ribs per 0.1 mm). Internal constriction present, but not conspicuous. Spiral ridges between radial ribs very fine, evenly-spaced, distinct and are present on all whorls except the protoconch. Shell rimately perforate, last whorl loosely-coiled, slightly detached, revealing a deep umbilicus. Aperture simple, circular, white. Peristome simple, well-rounded, thickened and reflected at the parietal area but not the palatal or basal area, not touching the ultimate whorl. Operculum not examined.

Dimensions ( Table 1). Shell height 0.80–0.90 mm, mean 0.85 mm; Shell width 0.34–0.35 mm, mean 0.35 mm; Aperture height 0.24–0.42 mm, mean 0.31 mm (n=3).

Etymology. From the Greek micro , meaning small, in reference to the remarkably smaller shell of matured individuals of the species compared to its four known congeners.

Habitat and ecology. Arinia (Notharinia) micro inhabits thickly vegetated lowland rainforest on and near limestone karsts. Living individuals were observed crawling among leaf litter and plant debris in sheltered and damp microhabitats near limestone rock outcrops.

Conservation status. This species is vulnerable to habitat loss as the Gunung Rapat karst complex is completely isolated from other natural rainforest and karst habitats because of intensive human developments, such as ex-tin mining ponds, agriculture, roads and residential areas. Although the type locality is within cave temple grounds, which provides the local population of Arinia (Notharinia) micro nominal protection from other land uses, the southern and central parts of the same karst complex are being rapidly subjected to destructive limestone quarrying activities.

Remarks. Arinia (Notharinia) micro notably differs from its congeners by its distinctly smaller shell. Like other Arinia (Notharinia) species, specimens of Arinia (Notharinia) micro may vary slightly in shell size (see Table 1), which has been suggested to be due to sexual dimorphism by Maassen (2008). Matured shells of Arinia (Notharinia) micro consistently comprise of 4.5 whorls compared to 4.5–5.0 whorls in Arinia (Notharinia) linnei , 5.0–5.4 whorls in Arinia (Notharinia) attenuata , 4.1–4.5 whorls in Arinia (Notharinia) brevior and 5.5 whorls in Arinia (Notharinia) crassilabris .

The radial ribs in Arinia (Notharinia) micro are more pronounced and well-developed compared to Arinia (Notharinia) linnei . The ultimate whorl of Arinia (Notharinia) micro is more loosely coiled and detached than Arinia (Notharinia) brevior and is distinct from the tightly coiled Arinia (Notharinia) attenuata , Arinia (Notharinia) crassilabris and Arinia (Notharinia) linnei . The deep umbilicus is visible in Arinia (Notharinia) micro , a feature not found in other congeners except Arinia (Notharinia) linnei . The umbilicus of Arinia (Notharinia) linnei is only partially visible due to obstruction by the ultimate whorl. The peristome of Arinia (Notharinia) micro is simple, a feature shared by only one other species, Arinia (Notharinia) attenuata . Interestingly, fine spiral ridges between the radial ribs are present in both Peninsular Malaysian species, Arinia (Notharinia) micro and Arinia (Notharinia) linnei , but is absent in the Vietnamese species (see Vermeulen et al., 2007).

Figures

Fig. 1. Shells of Arinia (Notharinia) micro Marzuki & Foon, new species. A–E, Holotype (BOR/MOL 6227): A, right lateral view; B, frontal view; C, apertural view; D, left lateral view; E. bottom view; F. paratype 1 (BOR/MOL 6228/1); G, paratype 2 (BOR/MOL 6228/2).

Fig. 2. SEM images of Arinia (Notharinia) micro Marzuki & Foon, new species, holotype (BOR/MOL 6227). A, sub-frontal view of the holotype; B, top whorl of the holotype; C, Radial ribs and spiral ridges on the surface of the holotype shell. Abbreviations: PA = Parietal side of the aperture, IC = Internal constriction, DRR = Dense radial ribs, LRR = Loose radial ribs, SU = Suture, TL = teleoconch, PR = protoconch, RR = Radial rib, SR = Spiral ridges.