Ampelita beanka Griffiths & Herbert 2013, sp. n.
Creators: name: Griffiths, O. L.
name: Herbert, D. G.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Stylommatophora
Acavidae
Ampelita
Ampelita beanka

description: Ampelita beanka sp. n.
Figs 15, 16, 17A, 17B
Etymology: Named after the type locality, Tsingy Beanka.
Diagnosis: Profile distinctive due to low spire, strongly shouldered whorls and descendant suture; umbilicus wide; protoconch with close-set axial riblets; teleoconch with close-set lamellate axial pliculae; lustreless, more or less uniformly mid to dark brown.
Description:
Shell: Relatively small with sharply angled periphery situated well above mid-whorl; spire very low, frequently almost flat; apical surface of whorls weakly convex, becoming slightly concave toward periphery; suture shallowly indented, but progressively descending below peripheral keel on last adult whorl giving shell a stepped profile; umbilicus wide, its rim roundly angular. Protoconch of 1¼–1½ whorls, max. diameter variable 3.7–4.1 mm; initially smooth, rather flat and somewhat sunken, thereafter more convex, bearing numerous, close-set, curved, axial riblets; riblets occasionally bifurcating or anastomosing (Fig. 17A). Teleoconch of a further 2–2¼ whorls; sculptured by closeset, axial pliculae, each with a thin periostracal crest in living specimens, rendering the pliculae somewhat lamellate (Fig. 17B); growth irregularities frequent; basal sculpture the same, continuing into umbilicus. Aperture rounded basally, somewhat angled at periphery and flattened above this; strongly oblique to vertical axis of shell; peristome incomplete, interrupted in parietal region; rim of peristome slightly thickened and flaring in adult, more strongly so basally.
Shell lustreless with a well-developed, predominantly mid to dark brown periostracum when fresh; slight radial unevenness in intensity; apical whorls often slightly paler; umbilicus commonly darker internally, its margin sometimes delineated by a paler band, but this rarely evident in fresh material.
Dimensions: Holotype, max. diameter 17.7 mm, height 8.0 mm; largest specimen, max. diameter 19.1 mm.
External features: Data on coloration of living animals not available; in preserved specimens head-foot mostly dark brown to blackish, but with evidence of a paler longitudinal band extending down neck from each optic tentacle; skin texture uniformly granular; lining of mantle cavity heavily pigmented with black and patterned with pale circular blotches, mostly on the right (upper) side.
Distal genitalia (Fig. 16): Relatively simple and largely typical of the genus. Penis short to moderate in length (4.0–5.0 mm) and rather stout; vas deferens running beside and loosely attached to its basal portion, but becoming more closely attached near penis apex; at apex of penis vas deferens turns sharply back on itself and broadens noticeably before inserting some distance below penis apex; this latter portion, perhaps constituting an epiphallus, has a thicker, pale flesh-coloured wall and is fused to outer wall of penis. Penis retractor muscle attaches apically, enveloping recurved portion of vas deferens and penis apex. Interior of penis with a Y-shaped longitudinal fold in the centre of which is a distinct, rounded papilla at insertion of epiphallus; this primary fold bordered on each side by a further longitudinal fold; remainder of lumen largely smooth, but with evidence of microscopic papillation in apical region. Genital atrium and vagina, simple and short; bursa copulatrix duct long, basal portion somewhat broader; bursa itself of moderate size, ovate to subcircular.
Holotype: MADAGASCAR: Central W Madagascar, ca 60 km E of Maintirano, in tall dense dry forest growing above cliffs on E side of Tsingy Beanka at Andohanandranogedro, 18.05028°S 44.53786°E, 380m, iv.2009, R. Randalana, st’n R04/09 (AMS C.474166, body in alcohol).
Paratypes: Same data as holotype (NMSA L8504 /T2983, 9 specimens, bodies in alcohol; NHMUK 20120014, 1 specimen); st’n 07/10 (NMSA L8525 /T2980, 6 specimens); st’n 07/09 (NMSA L8501 /T2981, 4 specimens, one in alcohol); st’n R01/09 (NMSA L8507 /T2982, 2 specimens); st’n 01/10 (AMS C.469583, 4 specimens; TMAM T165, 1 specimen); st’n 09/09 (MNHN IM-2010-20071, 1 specimen).
Additional locality data: Tsingy Beanka: st’ns 11/06, 09/09, 01/10.
Distribution: A narrow-range endemic currently recorded only from Tsingy Beanka.
Habitat. Fresh dead shells found most commonly in and amongst limestone rocks predominantly in the taller moister forests. Living individuals usually found in leaf-litter.
Remarks: In terms of its shape and coloration, A. beanka resembles A. milloti and A. namerokoensis (below), both of which occur in the Bemaraha-Beanka region. A. namerokoensis differs in lacking significant axial sculpture on the protoconch and in having distinct spiral microsculpture on the teleoconch (Fig. 17E, F). It also attains a larger size, has the peripheral keel closer to mid-whorl, has a somewhat narrower umbilicus, and the suture, if descendant at all, is at most weakly so and then only near the end of the last adult whorl.
Ampelita milloti is perhaps more similar in having axial riblets on the protoconch and lacking spiral microsculpture, but its teleoconch sculpture is finer, the axial elements more irregular and fragmented, appearing granular rather than lamellate (particularly evident on the base). Furthermore, as in A. namerokoensis, the suture of A. milloti is never strongly descendant. The smaller size, shouldered profile, strongly descendant suture and lamellate axial sculpture of A. beanka render it distinctive. The descent of the suture below the peripheral keel, though characteristic of the species and well developed in the holotype, is somewhat variable in its extent, but usually commences at least one half whorl prior to the aperture. The position of the peripheral keel is also somewhat variable, lying closer to mid-whorl in some specimens (Fig. 15D).
We have considered the possibility that these differences may reflect ecological factors and that the stepped profile may result from damage to the mantle edge at the suture, as is evident in some specimens of both A. milloti and A. namerokoensis. However, the stepped profile of A. beanka is present in specimens showing no growth scars indicative of earlier damage to the outer lip, and we can consistently discriminate between A. beanka and the other two species in terms of the microsculptural differences detailed above. There are also significant differences evident in the morphology of the penis (see below). All three species occur in the Tsingy Beanka and have been found to cooccur at a number of sampling sites. Emberton (1999) described a similar lamellar axial microsculpture in A. analamerae Emberton, 1999, from far north-eastern Madagascar, but that species is larger, is keeled at mid-whorl and has a much more prominent spire and narrower umbilicus.
description: Published as part of Griffiths, O. L. & Herbert, D. G., 2013, New species of land snails (Mollusca: Gastropoda) from two isolated karst formations in central western Madagascar: Tsingy Beanka and Antsingimavo, with additional notes on other regional endemics, pp. 1-48 in African Invertebrates 54 (1) on pages 23-26, DOI: 10.5733/afin.054.0101, http://zenodo.org/record/7670100