Nanocochlea Ponder and Clark, 1993

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), pp. 1-66 : 40-42

Genus Nanocochlea Ponder and Clark (in Ponder et al.), 1993

Type species: Nanocochlea monticola Ponder and Clark in Ponder et al., 1993 (original designation).

Description

Shell. Minute to small in size (adults range from 1.6 to 2.5 mm in length), pupiform to elongate pupiform or elongate­conic. Protoconch of about 1.4–1.5 whorls, typically sculptured with uniform pitting; separation of protoconch from teleoconch distinct, with varix­like border. Teleoconch with spire much longer than length of aperture. Aperture ovate, slightly angled posteriorly, inner lip attached to parietal wall or partially to completely detached, although not markedly so, usually lower part not much separated from base; outer lip orthocline to opisthocline, weakly thickened, simple or with very slight reflection. Periphery rounded, base simple, imperforate in adults, rarely narrowly umbilicate in juveniles. All species described below are semi­opaque to opaque, white with a thin pale yellowish periostracum.

Operculum. Ovate, paucispiral, flat, yellowish; columellar edge slightly convex, outer edge strongly convex; outer surface simple, paucispiral, nucleus markedly eccentric; inner surface usually smooth with white smear or (in one species) large, broad peg.

Radula. Central teeth large, cutting edge broad, indented mid dorsally, with 4–5 cusps on either side of narrow sharp median cusp; narrow, unthickened lateral projections emerge at about 45º from mid laterally; base with short, narrow, rounded basal projection not extending beyond lateral projections; two basal cusps emerge from ventral face of tooth on either side of basal projection, innermost longest. Lateral teeth with short cutting edge, about 4–5 small cusps on inner side of narrow median cusp and 4–6 small cusps on outer side; neck prominent, near vertical; lateral flange more than twice as long as cutting edge; prominent U­shaped projection on base below cutting edge; inner edge short, inner side of base excavated. Inner marginal teeth with 21–38 tiny cusps on rather wide cutting edge (ratio of cutting edge to shaft on inner marginal teeth about ¼); sides approximately parallel, outer edge thickened. Outer marginal teeth narrow, thickened on inner edge, distal end with 17–29 minute cusps; ratio of cutting edge to shaft about ¼.

Head­foot. Simple, unpigmented, with long cephalic tentacles, unpigmented to lightly pigmented eyes present in weak bulges at outer bases of tentacles; snout of moderate length, tapering, weakly bilobed distally. Foot short, rounded posteriorly.

Non­genital anatomy. Pallial cavity elongate, osphradium large and oval, towards posterior end of ctenidium; ctenidium absent or with small (reduced from normal triangular type) ctenidial filaments; efferent vein very short to long (ctenidium occupying nearly entire length of pallial cavity to about ½). Hypobranchial gland variably developed. Kidney and pericardium usually about ½ in pallial roof; renal gland orientated longitudinally. Stomach usually with anterior chamber larger than posterior; long style sac moderately long; no posterior caecum. Rectum with long S­shaped coil; overlying but not indenting pallial oviduct.

Male reproductive system. Prostate gland about ½ within pallial cavity; compressed to oval in section, with very thin ventral wall; pallial vas deferens opens at about ⅓–½ length of pallial portion. Penis located on right side of head well behind base of right tentacle; lacking but has an inconspicuous to moderately developed swelling in the distal portion just behind a papilla­like distal end; distal portion long and tapering; medial part simple and parallel sided; basal part wide to moderate.

Female reproductive system. Ovary simple sac; coiled oviduct smooth, firm, not embedded in connective tissue, initially inverted U­shape, usually straight distal to seminal receptacle, usually reaching posterior end of bursa (sometimes a little more or less) then sharply bent to run anteriorly; Seminal receptacle ovoid to pyriform, with short duct, opening to oviduct, located opposite middle to ventral part of left side of bursa copulatrix. Bursa copulatrix medium to rather large, globular to pyriform, posterior to albumen gland except for small overlap on right side, either behind posterior pallial wall or extending to it; bursal duct arrises from anterior or ventro­anterior wall, simple to undulating, joins oviduct dorsally at posterior pallial wall or just in front of it. Common duct straight. Albumen gland with ½ or more within pallial roof, shorter to longer than capsule gland. Capsule gland compressed­oval in section, divided into three glandular zones, short anterior and posterior translucent white zones and long yellowish to orange middle zone; anterior end blunt to steeply tapering; genital opening short, terminal to slightly anterior of capsule gland. Ventral channel extended into weakly to moderately developed vestibule anteriorly. No brood pouch.

Distribution and habitat

Members of the genus are known from mountain lakes, seepages, streams and caves in southern Tasmania.

Remarks

Nanocochlea differs from Pseudotricula in its small, tall­spired pupiform to elongateconic shell with a thin, simple, orthocline to opisthocline, usually non­reflected outer lip. There are no obvious anatomical differences between the two genera and there is a rather minor radular difference—the basal tongue of the central teeth is narrower in Nanocochlea . The outer shaft on the lateral teeth is longer in species of Nanocochlea than in typical species of Pseudotricula but P. conica , P. arthurclarkei and P. progenitor also have a long shaft.