Gabbia tumida, Ponder, 2003

Ponder, Winston F., 2003, Monograph of the Australian Bithyniidae (Caenogastropoda: Rissooidea), Zootaxa 230 (1), pp. 1-126 : 63-64

Gabbia tumida n. sp.

Etymology Tumidus (L.) – swollen.

Type material

Ngumurra Nawaru (Claud Cave), Kimberley, WA, 18° 4.030'S, 125° 43.900'E, 28 JUL 1998, S.Eberhard, (Holotype, WAM, S10885 ; paratypes, WAM S10879 , 13; AMS C.417604, 2) .

Additional material examined

Northern Territory: Limestone Gorge, Gregory Nat Pk, Victoria R Distr., NT, 16° 2.700'S, 130° 22.830'E, 30 JUL 1995, V.Kessner ( VKC 24372, 1 ; AMS C.318570, 1) .

Western Australia: Resurgence Cave , Kimberley, WA, 18° 4.030'S, 125° 43.900'E , 28 JUL 1998, S.Eberhard ( WAM S12736 , 20 +) .

Description

Shell ( Fig. 18K ) of moderate size (up to 5.5 mm in length), broadly­ovate to ovateconic, with up to 5.2 convex whorls. Protoconch of about 1.5 whorls. Teleoconch sculptured with fine collabral growth lines only; base evenly convex; umbilicus narrow to partially closed in both adults and juveniles. Aperture broadly­ovate; peristome with inner lip slightly thickened, outer lip thin and prosocline. Colour: shell semitranslucent white (“fresh”) to opaque white (“dead”); periostracum very thin.

Dimensions. See Table 16 for dimensions of holotype and Appendix, Table 29 , for summary shell dimensions and whorl counts.

Operculum and radula unknown.

Distribution ( Fig. 12 ) and habitat. This species is known from only three samples of empty shells. One in the Gregory NP is about 540 km distant from the others but all are inland from the Kimberley region. Two of the samples were found associated with limestone caves and the Gregory NP sample is also associated with limestone in an area where there are extensive caves. None of the material has been collected alive, or even contain the remains of the animal, although some specimens are recently dead. Whether this species lives within the cave system or outside it is unknown.

Remarks

This species is similar to the smooth­shelled species resembling G. vertiginosa ( G. campicola , G. rotunda , G. kendricki , G. pallidula etc.) but differs in having a smaller adult size than some of these species and from all but G. fontana , G. davisi and G. obesa in being narrowly umbilicate. G. tumida separates rather well from the other smooth umbilicate species, with 95% being correctly classified in a discriminant function analysis. It also separates well from G. smithii while G. napierensis , also from the Kimberley, is classified less successfully (see Fig. 17B, D ; Table 17 ). This latter species differs from G. tumida in having a smaller, more conic, imperforate shell and the aperture is thicker.

Figures

FIGURE 12. Distribution of Gabbia kendricki (), G. napierensis (), G. cf. napierensis () and G. tumida (o).

FIGURE 17. A ­ D, ­ Plots of the canonical scores obtained from a discriminant function analysis using all shell measurements and whorl counts. A, x – G. fontana; O – G. davisi; + ­ G. pallidula. B, x – G. obesa; O – G. smithii; + ­ G. tumida. C, x – G. fontana; O – G. davisi; + ­ G. obesa; ­ G. pallidula; ­ G. tumida. D, x – G. smithii; O – G. napierensis; + ­ G. tumida.

FIGURE 18. Shells: A, B, Gabbia rotunda, paratype, AMS, C.400134; C – F, Gabbia fontana, C, D, paratype, AMS, C.307903, E, AMS, C.380856; F, holotype, AMS, C.417672; G – J, Gabbia obesa, G, H, AMS, C.318584, I, paratype, AMS, C.417603, J, holotype AMS, C.417673; K, Gabbia tumida, holotype, S10885; Scales: A – K, 500 m.