Nanocochlea exigua, Ponder & Clark & Eberhard & Studdert, 2005

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 : 42-45

Nanocochlea exigua n. sp.

Figures 6H ; 8F ; 14A–C ; 15A–C ; 16A–C ; 17A–C ; 18A .

Type material

Holotype: AMS C.439393, Cane Toad Abuse streamway, Damper Cave, PB 1­2A, 28 MAR 1994.

Paratypes: AMS C. 203677, same data (20+ dry, 20+ wet) ; QVM, 9:20541 (5 wet).

Other material examined (all AMS)

Bauhaus: C.201820, stn PB6­1A (8 dry, 3 wet); C.201819, stn PB6­1A (1 dry); C,166855, Persephone Pot, stn PB17­8R (4 dry, 12 wet); C.201810, same locality, middle and upper streamway, stn PB17­2a.2 (7 dry); C.201814, same data (6 dry, 13 wet); C.201818, same locality, lower streamway, stn PB17­2a (1 dry); C.201274, Persephone, stn 7 (6 dry, 20+ wet); C.201461, Persephone streamway, stn 8 (7 dry, 20 wet); C.201455, same locality, stn 9 (6 dry, 20+ wet); C.201456, same locality, stn 10 (1 dry); C.201479, same locality, stn 10 (8 dry, 20+ wet); C.201462, Screaming Stals streamway, stn 12 (11 dry, 20+ wet); C.201480, same locality, stn 12 (5 dry); C.201457, same locality, stn 13 (1 dry).

Damper Cave: C.203683, main streamway near entrance, stn PB1­1A (3 dry); C.201465, main streamway, stn 6 (7 dry, 14 wet); C.439395, same data (2 dry, figd specimens); C.201482, Cane Toad Abuse streamway, stn 2 (8 dry, 20+ wet); C.201467, seep near The Keg, stn 3 (9 dry, 20+ wet); C.201475, Honey And Cream streamway, stn 4 (8 dry, 20+ wet); C.203679, Cane Toad Abuse streamway, stn PB1­2A (1 dry).

Damper Creek: C.203674, 10m outside Damper Cave, stn PBs­2A (2 dry, 1 wet).

Quetzalcoatl Conduit: C. 203672, stn PB3­1C (1 dry).

Etymology Exiguus Latin, small, short.

Description

Shell ( Fig. 6H ; 14A–C ; 15A–C ). Length up to 2.2 mm; elongate­conic (SW/SL 0.39– 0.61, mean 0.50, n = 37); spire tall, straight to slightly convex in outline; last whorl evenly rounded or with subshoulder depression; suture simple or indented/impressed. Protoconch microsculpture uniform ( Fig. 6H ). Teleoconch up to 3.7 whorls in adult; aperture oval to pear­shaped; small, shorter than spire (AL/SL 0.30–0.45, mean 0.36, n = 37); outer lip orthocline to opisthocline; weakly thickened in adult, straight; posterior notch absent; inner lip thin and narrow, in partial contact or narrowly separated from parietal wall.

Dimensions. See Table 10.

Operculum ( Fig. 16A–C ). Inner surface with white smear and 1 large peg.

Eyes. Unpigmented.

Pallial cavity ( Fig. 8F ). Ctenidium rudimentary with no filaments; osphradium present, as in other taxa; hypobranchial gland thick to moderately developed; renal organ extends forward ca. ⅓–½ into pallial cavity; pericardium more than ½ in pallial roof.

Radula ( Fig. 17A–C ). Central teeth: dorsal edge with deep indentation; 4–5 lateral cusps, median cusp narrow, blunt to sharply pointed, about twice as long as adjacent cusps. Lateral teeth: dorsal edge with shallow to moderate indentation; with 4–6 cusps on outer and 4–5 on inner side; median cusp narrow to medium width, blunt to sharply pointed, less than twice as long as adjacent cusps; ratio of cutting edge to shaft about ¼; basal projection bluntly pointed. Marginal teeth: Inner with 21–26 cusps; outer with 17–20 cusps.

Stomach. Stomach with posterior chamber a little smaller than anterior chamber.

Male genital system. Testis of 0.6–1.5 whorls; prostate gland about ⅔ in pallial roof, oval to kidney­shaped; compressed in section. Pallial vas deferens straight. Penis with weak swelling in mid­distal portion; distal end long, papilla­like; medial section parallel sided, of medium length; penial duct in medial section strongly undulating; base of penis very to moderately wide; with moderate folds; penial duct straight to weakly undulating.

Female genital system. ( Fig. 18A ). Ovary of 0.6–0.7 whorls; oviduct extends to posterior edge of bursa copulatrix or slightly less; joins bursal duct at posterior pallial wall. Bursa copulatrix large, extending to posterior pallial wall; elongately oval to pyriform; with bursal duct arising from antero­ventral to ventral edge of bursa; straight or with undulations. Seminal receptacle at middle of inner wall of bursa copulatrix or near mid ventral edge; ovoid to pyriform. Two thirds to all of albumen gland in front of posterior pallial wall; capsule gland about same length as albumen gland; oval in section; anterior end tapering to blunt; ventral channel simple, approximately parallel­sided throughout; vestibular area indistinct to distinct; genital opening overlapping anterior end of capsule gland to terminal.

Distribution and habitat

Found mainly in small, low energy streams and seepages in the caves. A few specimens were also found in Damper Creek 10 m outside Damper Cave.

Remarks

Nanocochlea exigua differs from other congeners in the operculum bearing a single large peg and in lacking a ctenidium (gill). In the former respect, it resembles some species included in Austropyrgus Cotton, 1942 ( Clark et al. 2003), as well as a number of other hydrobiid genera, including some found outside Australia. There are, however, several important characters that link N. exigua with Nanocochlea . There is no gastric caecum (present in Austropyrgus and several other genera bearing similar opercular pegs), the rectum is strongly S­shaped whereas in other genera with opercular pegs it is usually straight to arched. The female genital anatomy and penial morphology is also very like other species of Nanocochlea and unlike that of Austropyrgus . Assuming that the lack of the ctenidium in N. exigua has evolved from the presumed apomorphic condition seen in the other Precipitous Bluff congeners, and that no other species of Nanocochlea are known to possess an opercular peg, it is possible that the peg in this species is a secondary condition.

Figures

FIGURE 6. Protoconchs and teleoconch microsculpture of Pseudotricula and Nanocochlea species. A–D, Pseudotricula expandolabra, A, B, D, C.201493, paratype, main streamway, Bauhaus, C, C.201495, Persephone Streamway, Bauhaus; E–G, Pseudotricula conica, E, F, C.201464, Cane Toad Abuse Streamway, Damper Cave, G, Persephone Pot, Bauhaus; Honey and Cream Streamway, Damper Cave; H, Nanocochlea exigua, C.201475; I, J, Nanocochlea stylesae, C.201476, paratypes, Malani Creek; K–M, Nanocochlea damperensis, K, L, C.203685, paratypes, first crossing, Damper Creek, M, C.201282, Near New River Lagoon, E side, Limestone Ck, where tagged track crosses; N, O, Pseudotricula progenitor, C.201821, main streamway, Bauhaus. A, B, E, F, H, K–N, protoconch; C, D, G, I, J, O, microsculpture. Scales: A, C–E, J, K, M, O, 200 m; B, F–I, L, N, 100 m.

FIGURE 8. Pallial cavities of male specimens of Pseudotricula and Nanocochlea species. A, Pseudotricula expandolabra, C.201493, paratype, Persephone Streamway, Bauhaus; B, Pseudotricula arthurclarkei, C.203671, paratype, Quetzalcoatl Conduit; C, Pseudotricula auriforma, C.201496, paratype, main streamway, Damper Cave; D, E, Pseudotricula conica, D, C.203680, main streamway near entrance, Damper Cave, E, Cane Toad Abuse Streamway, Damper Cave; F, Nanocochlea exigua, C.203677, paratype, Cane Toad Abuse Streamway, Damper Cave; G, Nanocochlea damperensis, C.203685, paratype, first crossing, Damper Creek; H, Pseudotricula progenitor, C.201821, main streamway, Bauhaus. Scales: A–D, F–H, 500 m, E, 1 mm. Abbreviations: a, anus; ct, ctenidium; ev, efferent vein; os, osphradium; pc, pericardium; pe, pallial edge; ppw, posterior pallial wall; r, rectum; rg, renal gland. The stippled area represents the hypobranchial gland.

FIGURE 14. Shells of Nanocochlea species and Pseudotricula progenitor. A ­ C, Nanocochlea exigua, A, holotype, C.439393, Cane Toad Abuse Streamway, Damper Cave; B, C, C.201465, main streamway, Damper Cave; D, Nanocochlea stylesae, holotype, C.439398, Malani Creek; E–G, Nanocochlea damperensis, E, C.203685, paratype, first crossing, Damper Creek; F, holotype, C.439399, first crossing, Damper Creek, F, C.201282, Near New River Lagoon, E side, Limestone Ck, where tagged track crosses; H, I, Pseudotricula progenitor, H, paratype, C.439397, Persephone Streamway, Bauhaus; I, holotype, C.439396, Persephone Streamway, Bauhaus. Scales: 500 m.

FIGURE 15. Shells of Nanocochlea species and Pseudotricula progenitor. A ­ C, Nanocochlea exigua, A, C.203674, outside Damper Cave, Damper Creek B, C.166855, Persephone Pot, Bauhaus, C, C.201465, main streamway, Damper Cave; D–F, Nanocochlea stylesae, D, C.201476, paratype, Malani Creek, E, F, C.203686, first crossing, Damper Creek; G­I, Nanocochlea damperensis, G,H, C.303685, seepages at Bauhaus entrance, I, C.203685, paratype, first crossing, Damper Creek; J–L, Pseudotricula progenitor, J, L, C.201463, paratype, Persephone streamway, Bauhaus, K, C.201454, Persephone, Bauhaus. Scales: 1 mm.

FIGURE 16. Opercula of Nanocochlea species and Pseudotricula progenitor. A ­ C, Nanocochlea exigua, C.203677, paratypes, Cane Toad Abuse Streamway, Damper Cave; D ­ F, Nanocochlea damperensis; C–E, C.203685, paratypes, first crossing, Damper Creek; F, C.201282, Near New River Lagoon, E side, Limestone Ck, where tagged track crosses; G, H, Pseudotricula progenitor, C.201821, main streamway, Bauhaus; A, D, G, outer side; B, C, E, F, H, inner side; Scales: A, B, D, 200 m, C, E–H, 100 m.

FIGURE 17. Radulae of Nanocochlea species Pseudotricula progenitor. A ­ C, Nanocochlea exigua, A, C.201475, Honey and Cream Streamway, Damper Cave, B, D, C.201465, main streamway, Damper Cave; D– E, Nanocochlea stylesae, C.201476, paratypes, Malani Creek; G–K, Nanocochlea damperensis, G, H, C.203685, paratypes, first crossing, Damper Creek, I–K, C.201282, Near New River Lagoon, E side, Limestone Ck, where tagged track crosses; L–O, Pseudotricula progenitor, C.201821, main streamway, Bauhaus. A, E, central and lateral teeth; B, F, I, M, central, lateral, inner and outer marginal teeth; C, D, J, N central teeth; G, L, lateral teeth; H, central lateral inner and outer marginal teeth; K, outer marginal teeth. Scales: A, G–H, K, L, 10 m; B, I, M, 20 m; C, D, J, N, 5 m.

FIGURE 18. Female reproductive system of Nanocochlea species and Pseudotricula progenitor. A, Nanocochlea exigua, C.203677, paratype, Cane Toad Abuse Streamway, Damper Cave; B, Nanocochlea damperensis, C.203685, paratype, first crossing, Damper Creek; C, D, Pseudotricula progenitor, C.201821, main streamway, Bauhaus. Scales: 500 m. Abbreviations: ag, albumen gland; bc, bursa copulatrix; bd, bursal duct; cg, capsule gland; co, coiled oviduct; po, genital opening; pw, pallial wall; sr, seminal receptacle; vc, ventral channel.