Gabbia lutaria n.sp.

Etymology Lutarius (L.) ­ of mud.

Type material

Billabong 1.7 km W of East Baines R, N of Victoria Hwy, Victoria R District, NT, 15° 45.170'S, 130° 2.480'E, 27 JUN 1996, V.Kessner (Holotype, AMS C.417680; paratypes AMS C.318599, 41; AMS C.380764, 5; VKC 24320, 15); West Baines Minor R, S of Victoria Hwy, Victoria R District, 15° 55.970'S, 129° 44.670'E, 2 JUL 1996, V.Kessner (Paratypes, VKC 24321, 4); West Baines Minor R, 15° 56.020'S, 129° 44.660'E, shallow pools, in mud & on pool edges, 29 JUN 1999, W.F.Ponder (Paratypes AMS C.371666, 83 wet; AMS C.371668, 247 wet; NTM P21376, 8; WAM S10884, 5) .

Additional material examined

Northern Territory: Kings Billabong, 2 km SW of East Baines R , along Victoria Hwy, Victoria R district, 15° 46.780'S, 130° 0.870'E, 27 JUN 1996, V. Kessner (VKC 24319, 1); billabong at side of Victoria Hwy between Timber Ck TS and WA border, 15° 45.180'S, 130° 2.650'E, on mud, 27 JUN 1996, W.F.Ponder, A.C.Miller, D.L.Beechey & V. Kessner (AMS C.318735, 32) .

Description

Shell (Fig. 36A) very small (up to 2.7 mm in length), broadly­ovate, with up to 4.0 convex whorls. Protoconch of about 1.5 smooth whorls. Teleoconch sculptured with close, narrow axial ribs crossed by fine, close spiral lirae; base evenly convex; umbilicus moderate to wide. Aperture broadly ovate; peristome moderately thickened in adults; outer lip prosocline. Colour: shell opaque to semitranslucent, periostracum thin, white to pale yellowish­brown.

Dimensions. See Table 25 for dimensions of holotype and Appendix, Table 29, for summary shell dimensions and whorl counts.

Operculum (Fig. 32I,J) typical of genus. Ovate, slightly concave, translucent colourless to yellowish, concentric growth lines only in most specimens, one or two distinct ridges in some; inner surface with muscle scar occupying most of surface, sculptured with very weak concentric folds.

Radula (Appendix Table 30; Fig. 33L,M) typical of genus. Central teeth with 2­3 cusps on either side of median cusp which is about 1.4­1.5 longer than adjacent cusps and its base slightly wider to about 1.3 as wide; median cusp tapering to a sharp point. Face of central tooth with 3­4 pairs of cusps that extend to just inside lateral margin forming cuspate ridge, inner pair much larger than others, nearly half total height of tooth; lateral margins slightly convex to slightly concave, at about 50­60º; basal tongue moderately long, triangular, bluntly pointed. Lateral teeth with cusp formula 2­3 + 1 + 3­5; with cutting edge about 0.42­0.45 length of lateral part of tooth; median cusp about 1.5 as long as adjacent cusps, proximately parallel­sided to very slightly tapering, distally rapidly tapering to point or rounded; upper edge of lateral part of tooth at about 60­70º to cutting edge, lateral edge straight to slightly concave. Inner marginal teeth with 17­23 cusps, outer marginals with 10­12 cusps.

. Head foot and anatomy not examined.

Distribution (Fig. 35) and habitat. This species lives in fine mud in pools in the East and West Baines Rivers, both western tributaries of the Victoria R in the western Northern Territory.

Remarks

This species is very similar to G. adusta n. sp. but differs in its smaller size and relatively shorter spire. A discriminant function analysis separated all specimens of G. lutaria from G. adusta and G. clathrata n. sp. (Fig. 38).

FIGURE 38. Plot of the canonical scores obtained from a discriminant function analysis using all shell measurements and whorl counts; x ­ G. clathrata; O ­ G. adusta; + ­ G. lutaria .