Gabbia rotunda Ponder 2003, n.sp.
Creators: name: Ponder, Winston F.
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Bithyniidae
Gabbia
Gabbia rotunda

description: Gabbia rotunda n.sp.
Etymology Rotundus (L.) – round, spherical.
Type material
Spring on Doongmabulla Stn, ca. 7 km S of Carmichael Ck, ca. 50 km SW Beylando Crossing, Qld, 22° 5.449'S, 146° 14.425'E, in small seeps flowing from low mound and in damp mud out of the water., 4 MAY 2001, W.F.Ponder & C.Lydeard (Holotype, AMS C.417670; paratypes, AMS C.400139, 731 wet, 2 dry; QM, MO71712, 10).
Additional material examined
Queensland: 177.8 km from Marlborough turnoff to inland road, unnamed swampy Ck on Sarina ­ Marlborough Inland Rd, 21° 50.890'S, 148° 55.910'E, on edges of creek, in mud and on leaves etc., 12 SEP 2000, W.F.& J.M.Ponder (AMS C.385439, 20+).
Description
Shell (Figs 3N,O, 18A,B) of medium size (up to 4.4 mm in length), broadly­ovate to ovate conic, with up to 4.5 convex whorls. Protoconch of about 1.3­1.5 smooth whorls. Teleoconch sculptured with very fine collabral close, micro­costae and exceedingly fine close spiral striae; base evenly convex; umbilicus narrowly open in juveniles, usually closed chink in adults or very small if open. Aperture broadly ovate; peristome thin or with inner lip moderately thickened; outer lip slightly prosocline. Colour: shell opaque to semitranslucent; periostracum varies from nearly white through pale yellow to yellow­brown. Several varices usually present, represented by darker, weak, thin ridge.
Dimensions. See Table 13 for dimensions of holotype and figured paratypes and Appendix, Table 29, for summary shell dimensions and whorl counts.
Operculum (Fig. 15L,M) typical of genus. Ovate, dirty white to brown, with several distinct concentric, sometimes frilled, growth ridges; inner surface with muscle scar sculptured with ill­defined irregular shallow pits and weak, irregular, short ridges.
Radula (Appendix Table 30; Fig. 21 A­C) typical of genus. Central teeth with 3­4 cusps on either side of median cusp which is up to about twice as long as adjacent cusps and its base about a third wider; median cusp elongate­triangular, evenly tapering and sharply pointed. Face of central tooth with 2­3 pairs of cusps lying just inside lateral margin, inner pair much larger than others, moderate in size (about a third of total height of tooth); lateral margins straight, at about 60­70º; basal tongue rather short, bluntly triangular. Lateral teeth with cusp formula 3­4 + 1 + 3­4; with cutting edge about 0.43­0.50 length of lateral part of tooth; median cusp about 1.5 length of adjacent cusps, tapering, pointed; upper edge of lateral part of tooth at about 60­70º to cutting edge, lateral edge concave. Inner marginal teeth with 17­20 cusps, outer marginals with 9­16 cusps.
Head­foot dark grey, snout dark grey with black spots, tentacles grey or with pale grey longitudinal line in middle, otherwise unpigmented. Mantle roof mottled, darker anteriorly.
Anatomy. Gill (Fig. 6D) with apices at about fifth of gill width from right, in some close to right edge in posterior third; 45­49 filaments (n=4). Osphradium opposite middle of gill. Penis (Fig. 7B) with accessory lobe and penial lobe about equal in length, accessory lobe with distal end swollen and sucker­like; accessory gland short. Pallial oviduct not examined (AMS C.400139).
Distribution (Fig. 9) and habitat. Known only from a large, swampy recharge spring on Doongmabulla Station in the catchment of the Belyando and Burdekin Rivers and material from one other locality near Mt White in the Isaac, Mackenzie and Fitzroy River catchments is also tentatively attributed to this species. Both locations lie between 21­23ºS in Queensland and are about 277 kms apart.
Remarks
The description is based on the type material only. The type series is smaller in size than the other lot (AMS C.385439) which is tentatively attributed to this species from eastern Queensland, which reaches 5.2 mm in length, but otherwise has similar shell features (Fig. 13,H,I, 14A; operculum Fig. 15J, K). The radular characters (Fig. 16K,L) are also similar, other than the lateral margins of the central teeth being weakly concave. The gill has more filaments (60­62 [n=2] compared with 45­49) and the penis and accessory gland are very similar.
The new species is similar to G. vertiginosa in radular features but has a smaller, more globose shell with microcostae. It differs from G. campicola in its more globose shell, presence of microcostae and in radular characters (less developed basal cusps, with the second pair much weaker than the innermost, nearly straight lateral margins of the central teeth, and nearly straight to weakly concave dorsal edge to the outer part of the lateral teeth). The shell morphology of G. rotunda is also similar to that of G. iredalei but that species has a much larger shell and has a relatively narrower cutting edge on the central teeth, which bear 4­6 cusps on the face (compared with 2­3 in G. rotunda), a shorter basal tongue and the lateral teeth have a more distinctly angled lateral edge.
The shell sculpture is reminiscent of G. affinis (see below) but is finer and less regular while the shell of that species is more elongate and the central teeth of the radula have multiple basal cusps.
Gabbia pallidula is similar in shell characters to G. rotunda but G. pallidula differs in its very pale shell, narrow umbilicus, unpigmented animal and more prominent secondary basal denticles. There is very fine spiral striae present in G. rotunda which is absent in G. pallidula (and G. fontana n.sp.).
description: Published as part of Ponder, Winston F., 2003, Monograph of the Australian Bithyniidae (Caenogastropoda: Rissooidea), pp. 1-126 in Zootaxa 230 (1) on pages 51-54, DOI: 10.11646/zootaxa.230.1.1, http://zenodo.org/record/5019111