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Pseudotricula Ponder, 1992

Diagnostic features

Shell moderate to large in size (adults 1.7 to 4.4 mm), conical. Protoconch of about 1.5 whorls, typically sculptured with small, close pustules with some coalesced into weak, irregular radial ridges; separation of protoconch from teleoconch distinct, with varix-like border. Teleoconch with spire much longer to slightly shorter than length of aperture. Aperture ovate, slightly angled and typically channelled posteriorly, inner lip attached to parietal wall or partially to completely detached, although never markedly so; usually lower part raised well above base. Outer lip usually prosocline, with terminal growth, typically markedly expanded and flared, simple in some species; weak external varix present in one species (P. elongata). Periphery rounded, base simple, imperforate in both adults and juveniles. Usually semi-opaque to opaque, white, sometimes yellowish or brownish; with a thin pale yellowish periostracum.

Operculum ovate, paucispiral, flat, columellar edge slightly convex, outer edge strongly convex; outer surface simple, paucispiral, nucleus markedly eccentric; inner surface with weak ridges (probably representing reduced pegs) or (more often) white smear only.

The anatomy very similar  to Nanocochlea – the ctenidium only occupies the anterior half of the pallial cavity and with the filaments reduced in size and narrower than the normal broadly-triangular type. Other common features include the long, S-shaped rectal coil, unpigmented eyes and similarities with the stomach and genital anatomy. All species of Pseudotricula have a penial swelling and an identical structure is also seen in some species of Nanocochlea.

The main differences between Nanocochlea and Pseudotricula are shell characters. The shell in typical Pseudotricula is larger and broadly conical in shape, rather than the elongate conic to pupiform shells seen in NanocochleaPseudotricula species also have a relatively large aperture that typically bears an expanded outer lip.

Classification

Class Gastropoda

Subclass Caenogastropoda

Order Littorinimorpha 

Superfamily Truncatelloidea

Family Tateidae

Genus Pseudotricula Ponder, 1992

Type species: Pseudotricula eberhardi Ponder, 1992

Original reference: Ponder, W. F. (1992). A new genus and species of aquatic cave-living snail from Tasmania (Mollusca: Gastropoda: Hydrobiidae). Proceedings of the Royal Society of Tasmania 126: 23–28.

Type locality: Black Curtain Streamway, Cueva Blanca, Precipitous Bluff caves, southwest Tasmania.

Biology and ecology

Members of this genus occur on smooth rock surfaces in fast-flowing falls in caves, or in streamways in caves on cobbles, gravel and silt.

Distribution

Species of Pseudotricula are restricted to stream and seep habitats in the Precipitous Bluff caves of southern Tasmania.

Further reading

Beesley, P. L., Ross, G. J. B. & Wells, A., Eds. (1998). Mollusca: The Southern Synthesis. Parts A & B. Melbourne, CSIRO Publishing. 

Ponder, W. F. (1992). A new genus and species of aquatic cave-living snail from Tasmania (Mollusca: Gastropoda: Hydrobiidae). Papers and Proceedings of the Royal Society of Tasmania 126: 23-28.

Ponder, W. F., Clark, S. A., Eberhard, S. & Studdert, J. B. (2005). A radiation of hydrobiid snails in the caves and streams at Precipitous Bluff, southwest Tasmania, Australia (Mollusca: Caenogastropoda: Rissooidea: Hydrobiidae s.l.). Zootaxa 1074: 1-66.