Nannobeliscus mariaisabelae, Miquel & Jaime, 2018

Nannobeliscus mariaisabelae View in CoL spec. nov.

Figs 1 View Fig -6, 12-17, Table 1

Diagnosis. Shell of medium size, 16 mm, turrited, almost smooth, with 12 whorls, rimate, columella not truncate, radular formula 17 +1 +17 with tricuspid teeth, penis with large verge, vas deferens inserting into base of epiphallus, vagina long and fusiform with one medial bulb where the duct of the small gametolytic sac opens.

Description

Medium size shell of approximately 16 mm, turrited, thin and without ornamentation, imperforate; it has 10 to 12 flat-convex whorls; first whorls rounded and tapering towards fourth, last whorl presents slightly concave periphery; surface almost smooth, with weak and irregular growth lines; sutures somewhat crenulate; rimate; columella not truncate; aperture small, ovate, almost vertical, outer lip simple and thin; periostracum yellowish-brown, worn; protoconch smooth and not well differentiated from teleoconch. Odontognate jaw. Radula: teeth tricuspid; central ones with incipient ectocones, and approximately one third the length of the lateral teeth; lateral teeth with long mesocone, lateral cones short and sharp, this asymmetry is less marked towards the marginal teeth, broader than long, with edges that can become somewhat serrated. Radular formula 7 + 10+ 1 + 10+ 7. Penis, vagina and gametolytic sac extremely delicate, almost transparent and elongated. Penis very long and thin, with two parts well differentiated, the first has triangular and large verge, and opens into genital atrium with angle of approximately 90°; epiphallus present, penis muscle retractor inserting at base; vas deferens runs parallel to the penis between the atrium and its base where it inserts. Vagina long and fusiform with medial bulb; gametolytic sac small, runs parallel to the vagina and opens though large duct in the medial bulb. Spermatophore is fusiform, 800 µm in length, with three different parts, head, body and tail, found in the muscular bulb of vagina. Species ovoviviparous.

Measurements of the Holotype: 14.95× 3.40 mm; 12.00 whorls (see Table 1).

Type locality: Las Capillas , Jujuy, Argentina .

Repository ( in alcohol): Holotype: MACN-In 39.149, Las Capillas, Jujuy; – 6 Paratypes: MACN-In 39.150, Las Capillas , Jujuy.

Other studied materials: FIML 1219 , Holotype, Obeliscus (Nannobeliscus) siloaeoagus Weyrauch, 1967 , Central Peru, Leoncio Prado province , Huánaco department, right bank of Monzón River. MACN-In 36.941, Las Capillas, Jujuy. Col. M. Birabén, 4-XII-1951. 48 exs.

Etymology. Dedicated to María Isabel Hylton Scott (1889-1990), a prominent Argentinean malacologist.

Comparisons. Nannobeliscus was created as a new name after the nomen preoccupatum Microbeliscus Weyrauch, 1964, described as subgenus of Obeliscus Beck, 1837 (Weyrauch 1967). Schileyko (1999) included it in his monograph as a genus. Hausdorf et al. (2012) cited it, doubtfully, in the synonymy of Ischnocion Pilsbry, 1907 . But the genital features confirm the validity of the genus Nannobeliscus . Thus, the results of this research oppose the recent classification by Bank (2017).

Nannobeliscus siloaeoagus has an uniform cornyellow shell, with 9.5 whorls, and very low, broad radial plicae, parietal wall with filiform lamella, columella with low spiral lamella; 8.3 × 1.9 mm; soft parts remain unknown (Weyrauch 1964). It has less size and fewer whorls than N. mariaisabelae spec. nov. (16 versus 8.3 mm; 12 versus 9.5 whorls), its periostracum is brilliant while in the new species is opaque. In N. mariaisabelae , the shell is more fragile and the crenulation of sutures is much less marked than in N. siloaeoagus .

Respect to the type species of Opeas , Bulimus pumilum (= Helix goodali Miller, 1822 , homonymous of Helix goodali Férussac, 1821 ), it has different dimensions, such as number of whorls, length and width. The new species is bigger, lacks radial ornamentation (striae or wrinkles) and the outer lip is not arched forwardly (Pilsbry 1946, Virgillito 2012).

Leptinaria Beck, 1837 has a small penis, internally nearly smooth, long and slender flagellum, penial retractor attached to flagellum apically, and vagina with spiral folds internally ( Schileyko 1999). Its type species, Leptinaria unilamellata (d’ Orb., 1835) has small vagina and spermatheca, large flagellum and radular formula with marginal teeth very sharp and elongated, bicuspid (16+12 +1+12 +16) (Baker 1945).

Subulina Beck, 1837 shows a short and free oviduct, the vagina is rather long, the spermatheca and the penis usually are reduced ( Schileyko 1999). Subulina octona (Bruguiére, 1792) , the type species of this genus, was introduced in several areas of the world by human transport. It has a flagellum, lacks epiphallus, radular formula with numerous teeth (36/30-1-30/36), and marked columellar notch (Pilsbry 1946).

Neobeliscus Pilsbry, 1896 , from Brazil, lacks an epiphallus, has short ducts, and the sinuous vas deferens ends in the distal part of the penis, the penis retractor arises from the columellar muscle; the only species of this genus ( Helix calcarius Born, 1780 ) is very large (95 mm in length) (Pilsbry 1907, Schileyko 1999).

Regarding Ischnocion Pilsbry, 1907 View in CoL distributed throughout Colombia and Argentina ( Hausdorf et al. 2012), the soft parts of the type species Leptinaria (Ischnocion) triptyx Pilsbry, 1907 View in CoL are not known. The genus differs from the new species by presenting in its adult stage the following structures: two strong columellar folds and medial spiral lamella that follows the outer lip without reaching the edge ( Schileyko 1999). Ischnocion birabeni ( Hylton Scott, 1946) View in CoL described for northern Argentina (Jujuy province), presents in pre-adult stages, palatal lamella not found in the adult, and a poorly developed columellar fold in mature specimens; radular formula (9 +3) + 5 +1 +5 + (3 +9) with multicuspid marginal teeth; penis, long and arched forms a terminal expansion where the epiphallus is inserted, receives the vas deferens and the distal end of the retractor muscle; the duct of the spermatheca is very short and does not exceed the middle region of the uterus ( Hylton Scott 1946, Hausdorf et al. 2012). Ischnocion conica Hausdorf et al., 2012 View in CoL shows a long and ovate spermatheca not reaching the albumen gland, and a short and conical penis without epiphallus and apparently without vas deferens ( Hausdorf et al. 2012).

Allopeas Baker, 1935 View in CoL is an American genus with species introduced in various parts of the world by anthropic transport, such as Allopeas gracile View in CoL . This genus has a bifid penial apex and caecum alongside the epiphallus, which is highly developed (Baker 1945).

The genus Beckianum Baker, 1961 , from Venezuela and French Guiana, shows short and broad structures and ducts; penis with flagellum, spermathecal stalk short, and sculptured shell by strong axial ribs with umbilicus minutely open ( Schileyko 1999).

This is the first record of the presence of a spermatophore for an American genus. Schileyko (1999) cites the following genera: Paropeas Pilsbry, 1906 from Indonesia and other countries by anthropic distribution (e.g. Hawaii) ( Naggs 1994) and Itiopiana Preston, 1910 from Africa. In the first case this structure was described as fusiform and short (480 × 70 µm), and consisting of solid head and porous tail ( Naggs 1994, Schileyko 1999). In the second gastropod, only a posterior fusiform fragment of a spermatophore was recuperated ( Schileyko 1999).In N. mariaisabelae , this structure shows collapsed structure of 800 µm, formed by differentiated head (225 µm), longer body (325 µm) and prolonged tail (250 µm) (Fig. 16).