Gabbia pallidula, Ponder, 2003

Ponder, Winston F., 2003, Monograph of the Australian Bithyniidae (Caenogastropoda: Rissooidea), Zootaxa 230 (1), pp. 1-126 : 41-46

Gabbia pallidula n. sp.

Etymology Pallidus (L.) – pale ( pallidula dim.)

Type material

Unnamed spring near Smokey Ck. near The Springs HS, ca 83 km NNE of Aramac, Qld, 22° 12.330'S, 145° 22.500'E, in pool at base of spring, 25 SEP 1984, W.F.Ponder and P.H.Colman (Holotype, AMS C.417667, paratypes, AMS C.308007,144 wet, 6 dry, 1 on SEM stub; QM MO71710, 5) .

Description

Shell ( Figs 3K , 13C,D ) small (up to 4.3 mm in length (type locality only)), ovateconic, of up to 4.2 convex whorls. Protoconch of about 1.3 whorls, with traces of faint spirals and wrinkles, last 0.3 whorls with weak growth lines. Teleoconch not clearly differentiated from protoconch, sculptured with fine collabral growth lines only; base evenly convex; umbilicus usually closed in juveniles and adults, sometimes very narrowly open. Aperture broadly ovate; peristome slightly thickened (when mature) on inner lip where it is slightly reflected; outer lip thin, prosocline. Colour: shell semi­transparent to subtranslucent, periostracum very thin, colourless to pale yellowish, edge of mature lip yellow. One or two narrow varices sometimes present.

Dimensions. See Table 8 for dimensions of holotype and figured paratype and Appendix, Table 29 , for summary shell dimensions and whorl counts.

Operculum ( Fig. 15C,D ) typical of genus. Ovate, white, concentric growth ridges indistinct or one or two distinct; inner surface with muscle scar occupying most of surface, sculptured with weak pustules and ridges.

Radula (Appendix Table 30 ; Fig. 16A ) typical of genus. Central teeth with 3­4 (rarely 5) cusps on either side of median cusp; median cusp to about 1.5 length of adjacent cusps and twice as wide, tapering and pointed. Face of central tooth with 2­4 pairs of cusps that lie well inside lateral margin, inner pair much larger than others, about quarter to third total height of tooth; lateral margins straight to slightly concave, at about 50­60º; basal tongue long, rather narrow and bluntly pointed. Lateral teeth with cusp formula 3­4 + 1 + 3­5; with cutting edge about half length of lateral part of tooth; median cusp up to about two thirds length of adjacent cusps, blunt to pointed; upper edge of lateral part of tooth at about 60­70º to cutting edge, lateral edge straight to slightly to moderately concave. Inner marginal teeth with 20­23 cusps, outer marginals with 11­14 cusps.

Head­foot and mantle unpigmented.

Anatomy. Gill with apices at about quarter to third gill width from right; 48­52 filaments (n=2). Osphradium opposite middle of gill. Penis with accessory lobe slightly longer than penial lobe, not expanded distally; accessory gland medium length. Pallial oviduct similar to G. vertiginosa , with large seminal receptacle embedded in outer wall of albumen gland; bursa copulatrix narrow (about third height of capsule gland), at inner ventral side of capsule gland, extends to posterior end of capsule gland (AMS C.308007).

Distribution ( Fig. 9 ) and habitat. Known only from the type locality, an artesian spring, where it occurs in mud in the pool at the base of the spring.

Remarks

This species is similar to G. campicola and falls within the distribution of that taxon. Although G. pallidula lacks any distinctive shell features, other than being smaller, that separate it from typical G. campicola , a discriminant function analysis of these two taxa resulted in 100% successful classification of G. pallidula , although 14% of G. campicola were incorrectly classified. G. pallidula lacks a pigmented mantle and the gill apices are located further to the left than in G. campicola . In addition, the lateral teeth of the radula have a straighter dorsal margin, the median cusp on the lateral teeth has a rounded end in two of the three specimens of G. pallidula (pointed in all G. campicola examined) and there tend to be more cusps on the marginal teeth. The bursa copulatrix is also wider in G. pallidula than in the examined material of G. campicola .

This species also resembles G. fontana n.sp., G. davisi n. sp. and G. rotunda n. sp. and is contrasted in the remarks relating to those taxa. The unpigmented head­foot and mantle has not been seen in any other species in western Queensland other than one lot of G. fontana n. sp. (AMS C.307906) and one lot of G. campicola (AMS C.318702).

Figures

FIGURE 3.Protoconchs and microsculpure: A – E, Gabbia vertiginosa, A, B, AMS, C.308015, C – E, AMS, C.332890; F – I, Gabbia campicola, F – H, paratype, AMS, C.332829, I, AMS, C.318702; J, Gabbia kendricki, paratype, AMS, C.203378; K, Gabbia pallidula, paratype, AMS, C.308007; L, M, Gabbia napierensis, paratype, AMS, C.337372; N, O, Gabbia rotunda, paratype, AMS, C.400134; A, B, F ­ J, L ­ N, protoconch, C ­ E, K, O, microsculpture; Scales: A ­ B, F ­ J, L, 100 m, C ­ D, N, 200 m, E, K, O, 20 m, M, 500 m.

FIGURE 9. Distribution of Gabbia vertiginosa (o), G. iredalei (), G. cf. iredalei (), G. campicola (), G. fontana (), G. pallidula (☆), G. davisi () and G. rotunda (

FIGURE 13. Shells: A, B, Gabbia campicola, AMS, C.318702; C, D, Gabbia pallidula, C, paratype, AMS, C.308007, D, holotype AMS, C.417667; E, Gabbia davisi, holotype, AMS, C.417668; F, G, Gabbia napierensis, F, paratype, AMS, C.337372, G, holotype, S10978; H, I, Gabbia cf. rotunda, AMS, C.385439; Scales: A – D, F – I, 500 m, E, 1mm.

FIGURE 15. Opercula: A, B, Gabbia campicola, AMS, C.318702; C, D, Gabbia pallidula, paratype, AMS, C.308007; E, F, Gabbia davisi, paratype, AMS, C.417617; G ­ I, Gabbia napierensis, paratype, WAM, 1006 ­76; J, K, Gabbia cf. rotunda, AMS, C.385439; L, M, Gabbia rotunda, paratype, AMS, C.400134; A, C, E, G, I, J, L outer side, B, D, F, H, K, M inner side. Scales: 500 m.

FIGURE 16. Radulae: A, Gabbia pallidula, paratype, AMS, C.308007; B, C, Gabbia campicola, AMS, C.318702; D, Gabbia fontana, AMS, C.307906; E, F, Gabbia davisi, paratype, AMS, C.417617; G – J, Gabbia napierensis, paratype, –AMS, C.337372; K, L, Gabbia cf. rotunda, AMS, C.385439. A, B, E, H, I, L, central teeth, C, half row of teeth, D, central and lateral teeth, F, J, lateral teeth, G, marginal teeth, K, lateral and marginal teeth; Scales: 20 m.