Ventania avellanedae ( Doering, 1881 )

Pizá, Julia, Cazzaniga, Néstor J. & Ghezzi, Natalia S., 2018, Redescription of Ventania avellanedae (Stylommatophora: Odontostomidae), a land snail endemic to the Ventania Mountain System, Argentina, Zoologia (e 17786) 35, pp. 1-11 : 3-7

Ventania avellanedae ( Doering, 1881)

Figs 1–20

Eudioptus avellanedae Doering, 1881: 64 , pl. 1, figs 2, 3; Breure 1974: 112.

Anctus (?) stearnsianus Pilsbry, 1896: 41 ; Baker 1963: 230; Breure 1974:124.

Odontostomus (Spixia) avellanedae : Pilsbry 1902: 91, pl. 11, figs 56–59.

Odontostomus (Ventania) avellanedae : Parodiz 1940: 229, fig. 5; Parodiz 1942: 334, pl. 3, fig. 27; Richardson 1993: 44.

Cyclodontina (Ventania) avellanedae : Parodiz 1944: 5; Parodiz 1957: 28; Fernández and Castellanos 1973: 281; Fernández 1973: 121; Cuezzo et al. 2013.

[?] Spixia avellanedae [sic]: Breure 1974: 125.

Ventania avellanedae : Burela et al. 2003: 176, Delhey et al. 2005: 11.

Type locality. Doering stated that this snail inhabit on “rocas cuarcíticas de la Sierra de Currumalan” [Quartzite rocks in the Curamalal sierra], and also in “cerros o promontorios de la Sierra de la Ventana, cerca del Fuerte Argentino” [mountains or promontories in Sierra de la Ventana, near Fuerte Argentino], i.e., 19 km west of Tornquist City (38°05’S – 62°13’W), on the road joining the National routes 35 and 33, on the banks of the Sauce Chico stream .

Diagnosis. Protoconch with waved axial ribs crossed by spiral lines. Penis retractor muscle inserted in the distal end of a short flagellum. Epiphallus long and cylindrical with a distal widening indicating the presence of an internal epiphallic gland. Internal wall of the penis with three areas of different sculpture. Internal wall of the vagina smooth. Middle portion of the bursa copulatrix duct distinctly enlarged, with an internal sculpture of lengthy longitudinal lamellae in the wide region proximal to the bursa copulatrix, and a thick wall with perpendicular zig-zag grooves in the distal one.

Redescription. Shell ( Figs 1–10). Elongate-ovate, glossy, tawny to brown in color, rather thin; sometimes with some dark brown bands irregularly spread, and marked growth lines; 6 to 7.5 moderately convex whorls with shallow but well defined sutures.

Elongate-ovate aperture occupying ⅓ of the total shell length and lacking any fold or lamella ( Fig. 1). Peristome slightly expanded and reflected ( Figs 1, 2); inner lip turning on the columellar region although with a sharp edge. Parietal callus thin but well-defined. Columellar axis slightly inclined rightwards. Umbilicus narrow ( Fig. 2).

Protoconch ( Fig. 3) with a finely costulated surface, with marked waved axial ribs that often branch, crossed by a weaker spiral striation. Protoconch of adult snails smooth as a result of erosion ( Figs 2, 4, 8). Protoconch-teleoconch boundary well-defined ( Figs 3, 8). Teleoconch with wrinkle-like growth lines ( Figs 1, 2, 8–10).

Shell measurements (in mm): SL: 21.85 ± 1.76 (0.080) [18.33–26.07]; SW: 7.86 ± 0.61 (0.078) [6.55–9.05]; LWL: 14.13 ± 0.92 (0.065) [12.26–16.07]; AL: 8.60 ± 0.78 (0.091) [6.90–10.36]; AW: 5.01 ± 0.45 (0.091) [3.90–6.00]; MA: 132.07 ± 3.19 (0.024) [125–138]; SA: 31.07 ± 2.76 (0.089) [26–39].

Cephalopodium ( Figs 2, 11). Greenish brown. Head shorter than the tail, which does not surpass the length of the spire. Optic tentacles about four times longer than fore tentacles. Buccal opening large, round, with a pair of well-developed rounded lobes or lower lip appendices, which do not extend over the mandible ( Fig. 11). Upper lip conspicuous but lacking a third buccal lobe or upper lip appendix.

Digestive system ( Figs 12–15). Buccal mass spheroidal. Mandible arquated ( Fig. 12), formed by 12 imbricated plates directed towards the central zone. Central plates rectangular, more or less narrow, of variable width; lateral plates from rectangular to triangular, of uniform size; the more external plates are much larger, almost twice as long as the central ones. The surface of the plates is smooth; their borders are projected outwards, generating an irregular outline.

Radular teeth transversally arranged on a straight line ( Fig. 13). Central tooth tricuspid and smaller than the lateral ones ( Fig. 14); central cusp or mesocone of the central tooth romboid, with a free border that usually reach the basal part of the tooth; lateral cusps or ectocones much shorter than the central one. Lateral teeth bicuspid, with a long mesocone and a small ectocone located in an opposite position to the central tooth ( Fig. 14). Marginal teeth bicuspid, with a thin sharpen mesocone and a smaller ectocone, similar each other; inserted between the normal bicuspid teeth, some teeth have a bifurcated ectocone giving the tooth a tricuspid aspect ( Fig. 15). The form of the teeth gradually varies towards the radula edges, the cusps becoming less definite. Despite the gradualness of the transition from lateral to marginal teeth, they are usually distinguishable because marginal teeth are more elongated, have a more developed free grasping edge and slender mesocones.

Pallial complex ( Fig. 16). Narrow and elongated, 18.55 mm long on average (16.40–22.45) including the mantle collar, extends along about one and a half whorl, i.e. roughly ¼ of the total length of the snail body. The pinkish triangular kidney occupies ¼ to ⅓ of the lung length. Internal structure of the kidney with longitudinal, ondulated lamellae, in close contact among them. On the upper zone of the kidney, lamellae are widened and more globose; however they do not demarcate different regions, as their inner structure is homogeneous.

The primary ureter runs along the rectal side of the kidney up to the top of the lung cavity; it then turns down along the rectum and forms the secondary ureter, which opens proximally in the ureteric pore at the level of the middle point of the kidney. From this point on, the secondary ureter is open and ends at the pneumostome.

The pericardium, located in the upper columellar side of the pallial system, is 1.75–2.55 mm long. It is continuous with the prominent pulmonary vein that runs parallel to the rectum and reaches the mantle collar. The afferent marginal vein branches out approximately from the distal third of the pulmonary vein, equalling about 45% of its length. Adrectal area between the rectum and the pulmonary vein and between the pulmonary vein and the marginal afferent vein with a moderate vascularization. A marginal vein of weak development branches out from the last portion of the pulmonary vein and runs along the mantle collar border. The interramus area is deeply excavat- ed and of variable shape, either triangular or rectangular. The mantle collar includes a whitish spongy pallial gland.

Genital system ( Figs 17–20). Ovotestis composed by groups of acini extending over the inner, excavated face of the third whorl of the digestive gland. Collecting channels going out the ovotestis lead into the hermaphrodite duct, a twisted duct with a swollen central portion forming the vesicula seminalis. It ends at the white fertilization pouch-spermathecal complex composed by a proximal swollen portion and a thin, long blind sac ( Figs 17, 20). This complex is visible on the basal side of the albumen gland. The hyaline-yellow albumen gland is elongated, folded over its basis, and lies against the fore concave surface of the digestive gland over the digestive pouch.

Spermoviduct long and very curvilineal formed by the twist- ed, hyaline orange uterus, ending at the free oviduct and the white and glandular prostate, and continuous with the vas deferens.

The bursa copulatrix is spherical, and its duct is longer than the spermoviduct, which has two portions of different diameter. The part proximal to the bursa copulatrix slightly broadens towards the transition point at the distal third, where its diameter decreases by half and slightly widens again towards the end. The inner wall presents a characteristic sculpture. The proximal wide region has lenghty longitudinal lamellae, while the distal one has a thick wall with perpendicular zig-zag grooves ( Fig. 19). The duct of the bursa copulatrix and the free oviduct empty into the short and cylindrical vagina with spongy but smooth inner wall.

The vas deferens is a tubule of constant diameter that emerges just above the bifurcation of the vagina to the free oviduct and the bursa copulatrix duct. It runs attached to the vagina and the penial complex surface, passing underneath the penis sheath, and finally gets into the epiphallus–flagellum boundary. It is clearly visible and of thick diameter.

The male terminal genitalia or phallic complex is composed by a well delimited flagellum, epiphallus and penis. Flagellum, short and thin, occupies ⅑ of the phallic complex; the small and thin retractor muscle inserts on its distal end ( Fig. 17). The limit between flagellum and epiphallus is marked by the calibre shift and the entering of the vas deferens. The epiphallus is longer than flagellum and penis, occupies about ⅔ of the phallic complex, presents a distal widening indicating the presence of an internal epiphallic gland, and its inner wall presents four well defined straight folds. The limit between epiphallus and penis is demarcated by a constriction. Penis occupies about ⅕–¼ of the phallic complex. It is cylindrical and relatively slender, with a strong muscular wall. A short muscular sheath surrounds its distal end ( Fig. 17). Inner wall of the penis with folds and pilasters delimiting three different regions ( Fig. 18): the proximal region, with longitudinal irregularly festooned pilasters and folds in the direction of penis length; the medium region, with transversal lamellae; and a distal, variable portion that has thin irregular longitudinal folds in some specimens and a spongy surface in others.

Distribution and habitat. Ventania avellanedae is endemic to the Ventania Mountain System , in southern Pampas, Argentina. This area was included in the biogeographic Chacoan Subregion, Pampa province by Morrone (2006). The distribution of the species is restricted to mountainous environments, mainly living in rock crevices, but it can be also found under rocks or associated to plants in rocky microhabitats ( Delhey et al. 2005), so it is a rock dweller species as defined by Heller (1987).