Gabbia davisi Ponder 2003, n. sp.

Gabbia davisi n. sp.

Etymology

Named for Assoc. Prof. Andrew Davis, University of Wollongong, NSW, Australia, in appreciation of his companionship and assistance in the field.

Type material

Lake Huffer Stn, large spring near lake, pool at base of spring, Qld, 22° 15.660'S, 145° 20.430'E, in mud, 4 OCT 2002, W.F.Ponder & A.Davis (Holotype, AMS C.417668; paratypes AMS C.417617, 414 wet, 5 on SEM stub; QM MO71711, 10).

Description

Shell (Fig. 13E) medium (up to 6.7mm in length), broadly­ovate­conic, up to 4.6 convex whorls. Protoconch of about 1.3­1.5 almost smooth whorls, with traces of extremely fine spiral striae, last half whorl with weak axial threads. Teleoconch sculptured with fine collabral growth lines only; base evenly convex; umbilicus narrowly open, wider in juveniles. Aperture broadly ovate; peristome thin; inner lip slightly thickened, outer lip thin, prosocline. Colour: shell opaque to semi­translucent; periostracum pale yellowish to yellowish­brown. A few thin, rather indistinct, pale brown varices sometimes present.

Dimensions. See Table 9 for dimensions of holotype and Appendix, Table 29, for summary shell dimensions and whorl counts.

Operculum (Fig. 15E,F) typical of genus. Ovate, white; with several distinct concentric growth ridges; inner surface with muscle scar occupying most of surface, sculptured with weak pustules.

Radula (Appendix Table 30; Fig. 16E,F) typical of genus. Central teeth with 4­5 cusps on either side of median cusp which is up to about 1.5 length of adjacent cusps and its base up to about 1.5 width; median cusp tapering and pointed. Face of central tooth with 1 pair of prominent cusps about third to nearly half of tooth height; lie inside lateral margin with weakly denticulate ridge representing up to 4 additional rudimentary basal denticles; lateral margins straight to slightly concave, at about 50­60º; basal tongue rather long, narrow and blunt. Lateral teeth with cusp formula 3 + 1 + 3­4; cutting edge slightly less than half length of lateral part of tooth; median cusp about 1.5 length of adjacent cusps, tapering with blunt to pointed end; inner side with excavation at base, upper edge of lateral part of tooth at about 70º to cutting edge, lateral edge strongly concave. Inner marginal teeth with 15­21 cusps, outer marginals with 8­9 cusps.

Head­foot grey to black except for tentacles distal to eyes. Tentacles unpigmented except for grey stripe in middle. Mantle roof black with small to large, close white spots and patches giving it netted appearance. Visceral coil unpigmented to black dorsally.

Anatomy. Gill with apices at about third gill width from right; 55­61 filaments (n=3). Osphradium slightly posterior to middle of gill or at middle. Penis (Fig. 7C) and accessory lobe about equal in length to penial lobe or slightly longer, accessory lobe expanded to markedly expanded distally; accessory gland very long and tightly coiled. Pallial oviduct similar to G. vertiginos, with narrow bursa copulatrix reaching edge of albumen gland (AMS C.417617).

Distribution (Fig. 9) and habitat. Known only from a single spring on Lake Huffer Station in western Queensland where it was found in a small, shallow muddy pool near the head of a large spring and, abundantly, in a large, shallow muddy pool at the base of the spring outflow.

Remarks

This species closely resembles G. campicola in shell characters and measurements and in radular characters. Its whorls tend to be more convex and it is much more distinctly umbilicate, especially in juveniles which are rather widely umbilicate. Gabbia davisi differs from G. campicola in the gill apices being at about a third of the gill width (compared with on or close to the right edge). It also differs from G. campicola and all other similar species in the accessory prostate being unusually very long, narrow and tangled. The pigmented mantle, long accessory gland and umbilicus separate this species from G. pallidula. Gabbia davisi is found in a spring very near the type locality of G. pallidula, and is contrasted in the remarks under that species. Gabbia fontana n. sp., another spring endemic, is contrasted below under that taxon.

Despite the apparent lack of shell differences, a disciminant analysis including all similar species from NE Queensland separates this species reasonably well from G. campicola and other similar taxa (Figs 10D, 17A, C; Tables 10, 11).