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

description: Gabbia fontana n.sp.
Etymology Fons, fontis (L.) – spring.
Type material
Big Spring, ca 3 km SE of Edgbaston HS, ca 31 km NE of Aramac, Qld, 22° 45.083'S, 145° 25.600'E, outflow, 26 SEP 1984, W.F.Ponder & P.H.Colman (Holotype, AMS C.417672; paratypes, AMS C.307903, 592 wet, 36 dry, 9 on SEM stubs; AMS C.307904, 5; AMS C.307905, 7; QM MO71713, 8), same data, in small seep (AMS C.417918, 12), same locality, far end of spring near fence, amongst sedges, 5 MAY 2001, W.F.Ponder & C.Lydeard (AMS C.401245, 17 wet).
Additional material examined
Queensland: Springs on Edgbaston Stn, NE of Aramac, QLD: NE group, fenced spring, 22° 43.125'S, 145° 26.230'E, on mud, in spring outflow & at edges of outflow, 5 MAY 2001, W.F.Ponder & C.Lydeard, (AMS C.408298, 20+; AMS C.400141, 20+); near NW edge of springs, fenced spring on east side of track, 22° 43.000'S, 145° 25.633'E, middle of spring, 5 MAY 2001, W.F.Ponder & C.Lydeard (AMS C.401244, 20+); Little Western Spring, 22° 42.91'S, 145° 25.55'E, end of outflow, 26 SEP 1984, W.F.Ponder & P.H.Colman (AMS C.307906, 20+), same data, edge of spring (AMS C.307907, 1); “Pool 3”, near Edgbaston HS, 22° 43.16'S, 145° 26.09'E, lower outflow, SEP 1991, P.Unmack (AMS C.380856, 20+), same data, middle of spring, SEP 1991, P.Unmack (AMS C.380860, 20+), near head of spring (AMS C.380861, 20+); Blue Eye Spring, 22° 43.19'S, 145° 26.37'E, 30 SEP 1991, P.Unmack (AMS C.380862, 20+; AMS C.380863, 20+); Goby Spring, 22° 45.92'S, 145° 25.79'E, lower outflow, SEP 1991, P.Unmack (AMS C.380864, 20+), same data, near head, SEP 1991, P.Unmack (AMS C.380866, 20+).
Description
Shell (Figs 14B,C, 18 C­F) small to moderate (up to 5.2 mm in length), ovate­conic, of up to about 4 convex whorls. Protoconch of about 1.5 whorls, smooth except for extremely minute granules and faint spirals, last half whorl with weak growth lines. Teleoconch sculptured with fine collabral growth lines only; base evenly convex; umbilicus widelyopen in juveniles and open in adults. Aperture broadly­ovate; peristome thin; outer lip prosocline. Colour: shell thin, subtranslucent; periostracum pale yellowish­white.
Dimensions. See Table 14 for dimensions of holotype and figured paratypes and Appendix, Table 29, for summary shell dimensions and whorl counts.
Operculum (Fig. 20 A­C) typical of genus. Ovate, white, concentric growth ridges weak, one or two distinct growth ridges rarely present, typically much of outer surface eroded; inner surface with muscle scar occupying most of surface, sculptured with irregular, convoluted grooves and ridges.
Radula (Appendix Table 30; Figs 16D, 21 D­F) typical of genus. Central teeth with 2­5 cusps on either side of median cusp which is about 1.5 longer than adjacent cusps and its base twice as wide; median cusp tapering to sharp point. Face of central tooth with single pair of prominent cusps (about 0.3 total height of tooth) and, sometimes pair of weak denticles (very rarely 3 rd pair of denticles present); cusp lies well away from lateral margin; lateral margins straight, simple, at about 50­60º; basal tongue broad, rounded. Lateral teeth with cusp formula 2?­3 + 1 + 3­6; with cutting edge about 0.41­0.66 length of lateral part of tooth; median cusp up to about twice length of adjacent cusps, tapering, often with convex sides, end blunt to pointed; upper edge of lateral part of tooth at about 45­60º to cutting edge, lateral edge straight to slightly concave. Inner marginal teeth with 15­24 cusps, outer marginals with 7­21 cusps.
Head­foot unpigmented to dark grey or black except for distal half of tentacles which fade to unpigmented. Penis unpigmented to black. Mantle roof and visceral coil unpigmented to black.
Anatomy. Gill (Fig. 6C) with apices at quarter to third gill width from right; 39­47 filaments (n=5). Osphadium opposite middle of gill. Penis (Fig. 7F,G) with accessory lobe shorter to about equal in length of penial lobe, distal end slightly to moderately expanded, sucker­like; accessory gland short to very short. Pallial oviduct similar to G. vertiginosa but with relatively shorter albumen gland and larger seminal receptacle embedded in centre of ventral part of gland; bursa copulatrix reaching to end of capsule gland (AMS C.380863, AMS C.307903, AMS C.307906, AMS C.400141).
Distribution (Fig. 9) and habitat. This species appears to be restricted to artesian springs on Edgbaston Station near Aramac, western Queensland. A number of other endemic molluscs and fishes have been described from these springs (Ponder and Clark, 1990; Ponder, in press; Brown, 2001; Wager and Unmack, 2000). It lives in the shallow water on the edges of the outflows, or along the damp edges, and can be very abundant.
Remarks
The shell of G. fontana lacks distinctive sculpture and is thus superficially similar to the species resembling G. vertiginosa (including G. iredalei and G. campicola) but differs from all these in being distinctly umbilicate and in the central teeth of the radula having only two pairs of cusps on their lateral faces, the inner­most being moderately large, the outer pair being minute. G. fontana is also unusual in, when pigmented (the usual condition), the mantle roof is solid black rather than mottled.
This species is most similar to G. pallidula, which occurs nearby, in shell shape and size but that species differs in both juveniles and adults being imperforate or very narrowly perforate. In addition, the head­foot and mantle roof of G. pallidula are completely unpigmented whereas in G. fontana they are usually strongly pigmented, often black, although at least one lot (AMS C.307906) is unpigmented. The central teeth of the radula have only one pair of distinct basal cusps in G. fontana whereas there are at least two in G. pallidula. The two species have similar shell dimensions but discriminate reasonably well (85%) in a discriminant function analysis (see Fig. 10D, 17A; Table 11). Gabbia davisi n.sp., another species found in the Barcaldine Supergroup springs, close to the locality where G. pallidula is found, is discriminated well (95%) from both species (Figs 17A; Table 11; see also Fig. 10D and Table 10). That species differs from G. fontana in having a narrower umbilicus and a much longer accessory gland. Both species usually lack additional pairs of basal denticles but G. fontana does not have the incipient denticles seen in G. davisi.
The shell and operculum are often corroded. The opercula that are not corroded do not have the heavy concentric ridges seen in several other taxa that live in temporary wetlands and represent “rest” periods (e.g. G. vertiginosa). Similarly, the shells lack varices. The lack of these structures is probably because of the continuity of the artesian spring habitat. The considerable erosion often seen on the outer surface of the operculum in this species is unusual and has not been observed in other taxa.
One sample in which the head­foot and mantle roof are unpigmented in all specimens (AMS C.307906) also has weak denticles on the central teeth of some specimens but is similar to typical G. fontana in other respects.
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 55-60, DOI: 10.11646/zootaxa.230.1.1, http://zenodo.org/record/5019111