Nanotrachia, Köhler & Criscione, 2013

Köhler, Frank & Criscione, Francesco, 2013, Small snails in a big place: a radiation in the semi-arid rangelands in northern Australia (Eupulmonata, Camaenidae, Nanotrachia gen. nov.), Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 169 (1), pp. 103-123 : 118-119

NANOTRACHIA GEN. NOV.

Type species: Ordtrachia intermedia Solem, 1984 .

Description

Shell ( Figs 4 , 5 ): Relatively small, flat, thin to moderately thick; periphery rounded to strongly keeled; spire moderately to weakly elevated; umbilicus open, wide, rarely partly concealed by columellar reflection; protoconch and teleoconch with dense, pointed periostracal projections and fine axial growth lines; teleoconch with or without axial ribs; last whorl moderately wide in cross section; apertural lip reflected, moderately expanded, without lip nodes; parietal wall thin; colour uniform, horn to brown.

Genitalia ( Figs 6 , 7 ): Spermoviduct, lacking diverticulum and stimulatory organs. Penial sheath well-developed, extending entire length of penis, membranous. Penial retractor muscle inserting on vas–epiphallic junction; in some species muscular fibres extending onto penial apex. Epiphallus well developed; wall comprising thick layers of muscle; connected to penis through simple duct and pore; length equivalent to 20–100% of penis. Vas deferens entering penial sheath basally to halfway up, before reflexing into epiphallus. Penis thin with thin wall; not coiled within penial sheath; inner penial wall with between one and three narrow to thick, straight or winding, longitudinal pilasters, in some species with regularly spaced, pointed corrugations. Vaginal length equivalent to 50–100% of penis, twice as long as free oviduct. Bursa copulatrix simple, distally slightly inflated, comparatively short, extending to, or nearly to, anterior end of spermoviduct.

Comparative remarks

Shell easily distinguished from other camaenid genera from the VRD and EK by its small size, flat shape, open umbilicus, microscopic pustulation. Differing from Cristilabrum Solem, 1981 , Exiligada , Mesodontrachia , Ningbingia Solem, 1981 , Nodulabium Criscione & Köhler, 2013 , Ototrachia Criscione & Köhler, 2013 , Prototrachia Solem, 1984 , Pseudomesodontrachia Criscione & Köhler, 2013 , Turgenitubulus Solem, 1981 , and Vincentrachia Criscione & penis. Muscle fibres connecting median portion of epiphallus to penial apex. Vas deferens entering penial sheath halfway up. Inner penial wall with a single, wide, long, irregularly S-shaped pilaster, comprising apical two-thirds of wall. Vagina about as long as penis, from half to twice as long as free oviduct.

Comparative remarks

Shell similar to N. costulata sp. nov., differing from N. carinata sp. nov., N. coronata sp. nov., and N. orientalis by less developed peripheral keel, and from N. levis sp. nov. by presence of axial ribs. Genital anatomy differing from N. carinata sp. nov., N. coronata sp. nov., and N. levis sp. nov. by smooth penial wall pilasters and long epiphallus; differing from N. costulata sp. nov. by fewer number of pilasters (one instead of three).

Köhler, 2013 by smaller and less conical shape. Differing from most Ordtrachia species by smaller size and presence of axial ribs, and from O. elegans by stronger axial sculpture and periostracal projections. Differing from M. occidentalis ( Fig. 4G ) by callus not detached from parietal wall.

Figures

Figure 4. Shells of Nanotrachia species studied herein. A, N. intermedia (Solem, 1984) (paratype AM C.146110); B, Nanotrachia carinata sp. nov. (paratype WAM S49100); C, N. coronata sp. nov. (paratype WAM S49086); D, N. costulata costulata sp. nov. (WAM S49088); E, N. levis sp. nov. (paratype WAM S49096); F, N. orientalis (Solem, 1984) (paratype AM C.146105); G, Mouldingia occidentalis (Solem, 1984) (paratype AM C.146107). Scale bar = 1 cm.

Figure 5. SEM micrographs of shells showing protoconch and teleoconch microsculpture. A–B, N. carinata sp. nov. (paratype WAM S49100); C–D, N. coronata sp. nov. (paratype WAM S49086); E–F, Nanotrachia costulata sp. nov. (WAM S49088); G–H, N. levis sp. nov. (paratype WAM S49096). Scale bars: A, C, E, G = 1 mm; B, D, F, H = 200 Mm.

Figure 6. Penial anatomy. A, Nanotrachia intermedia (Solem, 1984) (WAM S49195); B, N. intermedia (Solem, 1984) (WAM S49194); C, Nanotrachia carinata sp. nov. (holotype WAM S66300); D, N. levis sp. nov. (holotype WAM S6630). Insets showing schematic cross section of mid-penis. Scale bar = 2 mm.

Figure 7. Intraspecific variation of penial anatomy in N. costulata sp. nov. A, Nanotrachia c. costulata (holotype WAM S66302); B, Nanotrachia c. costulata (WAM S49174); C, Nanotrachia c. montejinni ssp. nov. (holotype NTM P48939); D, Nanotrachia c. montejinni (AM C.437659). Insets showing schematic cross section of midpenis. Scale bar = 2 mm.