Allopeas clavulinum (Potiez & Michaud, 1838)

Bulimus clavulinus Potiez & Michaud, 1838, 1: 136, pl. 14, figs 9, 10. Type locality: “ L’île Bourbon ”, namely Réunion Island, Mascarene Archipelago. Type material: lost (Smith 1992: 309).

Material examined.

Italy • 6 shells and 6 spirit specimens; Trento, Tropical greenhouse of the Science Museum of Trento (MUSE); 46 ° 03 ' 45.16 " N, 11 ° 06 ' 50.08 " E; 14 Dec. 2017; A. Benocci, G. Manganelli, D. Miserocchi leg.; GMC 47556 • 623 shells, 10 spirit specimens; same locality; 04 Jan. 2019, 10 Feb. 2019, 04 May 2019; D. Barbato, G. Bolzonella leg.; GMC 51194 • 418 shells, 2 spirit specimens; same locality; 01 Feb. 2022; D. Barbato, A. Benocci leg.; GMC 51184 • 133 shells; same locality; 02 Feb. 2023; F. Rossi leg.; GMC 57343 • 155 shells; same locality; 9 Feb. 2023; D. Barbato, A. Benocci leg.; GMC 57350 • 145 shells and 1 spirit specimen; Padua, Biodiversity Garden (Botanical Garden of Padua); 45 ° 23 ' 52.59 " N, 11 ° 52 ' 50.37 " E; 06 Mar. 2019; D. Barbato leg.; GMC 57373.

Description.

Shell (Figs 1–6). Dextral, small, minutely perforate to imperforate, elongate, slender, conical, rather robust, pearly off-white, glossy and sub-transparent when fresh, with 5–7 slightly convex whorls, separated by moderately deep sutures. Apex obtuse, rounded, and smooth. Last whorl ~ 1 / 2 of shell height. Aperture small, ~ 1 / 3 of shell height, obliquely pyriform, slightly prosocline. Peristome interrupted, not thickened, only slightly reflected on columella, sometimes with slightly evident callous rim on parietum; columella straight; outer margin sinuous in lateral view (approximately inverse S-shaped). Protoconch smooth; teleoconch with thin and irregular collabral growth lines. Shell dimensions: SH 5.5–6.8 mm; SD 2.2–2.6 mm; AH 1.9–2.3 mm; AW 1.2–1.4 mm.

Female distal genitalia (Figs 9 – 12). Free oviduct long and wide. Bursa copulatrix sac-like, oval with long slender duct (slightly longer than bursa copulatrix), sometimes initially flared. Vagina short and wide (approximately as long as free oviduct) with small lateral bulge.

Male distal genitalia (Figs 9 – 13, 15, 16). Vas deferens almost uniform in diameter (very thin to thin along its entire length), entering penial complex at its proximal end. Penial complex consisting of epiphallus, penial caecum and penis. Epiphallus very short. Penial caecum very short (as long as epiphallus). Penis short to rather long, almost uniformly cylindrical, undivided, with penial sheath enveloping its distal tract. Penial retractor muscle bifid, one branch inserted on proximal end of epiphallus, one branch on tip of penial caecum.

Genital atrium (Figs 9 – 12). Rather long.

Remarks.

Although Allopeas clavulinum is a well-known greenhouse snail (Kerney and Cameron 1979), its taxonomic and systematic placement is still not definitive, nor is its native range clear. The species was first described from Réunion Island (as Île Bourbon), Mascarene archipelago, in the western Indian Ocean (Potiez and Michaud 1838), but Griffiths and Florens (2006) thought it an East African species introduced into the Mascarene islands. The hypothesis that the species is native to Africa or East Africa was also maintained by Kerney and Cameron (1979), Robinson (1999), Probst (2001), Shea (2007), Cowie et al. (2008), Stanisic et al. (2010), and Foon et al. (2017). However Rowson et al. (2010) observed that Verdcourt, familiar with A. clavulinum in botanic gardens of the UK, never reported it from East Africa (e. g., Verdcourt 1983, 2000, 2006). Alternatively an Asian / south-east Asian origin was proposed by Brook et al. (2010) and Rumi et al. (2010). Support for a south-east Asian origin could come from the putative finding of a shell in the Holocene of Thailand (Robba et al. 2007) and its membership of a molecularly based monophyletic group, including other species from Sri Lanka (Fontanilla et al. 2017).

Today, Allopeas clavulinum occurs in humid tropical and subtropical lowlands across the world. It is reported from the West Indies, South America, West Indian Ocean islands, South and South-east Asia, New Guinea, Australia, and Pacific islands. Outside the tropics and subtropics it only occurs in heated greenhouses or very disturbed habitats, mainly in the northern hemisphere. Indeed it has been reported from North America, Europe, the Middle East, and New Zealand (see Table 1 for details and references). An alleged distinct subspecies Allopeas clavulinum kyotoense (Pilsbry & Hirase, 1904) is reported from Korea and Japan (Minato 1988; Noseworthy et al. 2007).

The genital anatomy of Allopeas species is poorly understood. Earlier studies have been performed on specimens of Allopeas gracile (Hutton, 1834) from Puerto Rico (Baker 1945; Baker in Pilsbry 1946) and Suriname (Gittenberger and van Bruggen 2013), Allopeas clavulinum from Scotland (Baker 1945; Baker in Pilsbry 1946) and Brazil (Marcus and Marcus 1968), Allopeas mauritianum (Pfeiffer, 1853) from Mauritius (Baker 1945; Baker in Pilsbry 1946) and Allopeas “ spec. 2 and Allopeas spec. 3 ” from Pemba (Gittenberger and van Bruggen 2013). The overall distal genitalia organisation of our specimens (Figs 9 – 12) is consistent with that described in Allopeas gracile (Baker 1945: 88–89; Baker in Pilsbry 1946: 178, fig. 84.9; Gittenberger and van Bruggen 2013: 255, fig. 10), Allopeas clavulinum (Baker in Pilsbry 1946: fig. 84.6; Marcus and Marcus 1968: fig. 9), Allopeas spec. 2 (Gittenberger and van Bruggen 2013: 254–255, fig. 11) and Allopeas spec. 3 (Gittenberger and van Bruggen 2013: 255, fig. 12). However the relationships between the penial sheath and the vas deferens seem different from what was illustrated by Marcus and Marcus (1968), the only authors to describe them: according to Marcus and Marcus (1968: fig. 9) the vas deferens runs externally to the penial sheath whereas we found that it runs internally. The proximal penial complex consists of a short bulbous epiphallus and thin walled penial caecum with a branch of the penial retractor on the proximal tip of each (Figs 13, 15, 16). The epiphallus and the penial caecum are so closely juxtaposed as to resemble a usual proximal penis tip with an undivided penial retractor joined to it (Figs 9 – 12). This arrangement matches that already described in Allopeas gracile (Baker 1945: 88; Baker in Pilsbry 1946: 178, fig. 84.10), Allopeas clavulinum (Baker 1945: 90; Baker in Pilsbry 1946: 180, fig. 84.6; Marcus and Marcus 1968: fig. 9), Allopeas mauritianum (Baker 1945: 90; Baker in Pilsbry 1946: 180) and Allopeas spec. 2 (Gittenberger and van Bruggen 2013: 255, fig. 11 b). However there seems to be some variation, especially in the structure of the penial caecum between these species: Allopeas gracile and Allopeas mauritianum have a robust penial caecum, large at the base and progressively tapering towards the tip (for Allopeas gracile, see Baker in Pilsbry 1946: fig. 84.10; Gittenberger and van Bruggen 2013; for Allopeas mauritianum, see Baker in Pilsbry 1946: fig. 84.3), whereas Allopeas clavulinum has a long slender penial caecum almost uniform in diameter, thin along its entire length (Baker in Pilsbry 1946: fig. 84.4; Marcus and Marcus 1968: fig. 9). Based on penial caecum structure, our specimens apparently do not match those assigned to Allopeas clavulinum but are more similar to those assigned to Allopeas mauritianum. As already rightly observed by Gittenberger and van Bruggen (2013), it is not clear whether these differences are due to individual variation or to phylogenetic divergence. The relationships between these taxa are also uncertain, as is whether these names have been used consistently in the literature. Although they are currently regarded as synonyms (MolluscaBase eds 2024 b), their status and relationships are still not clear and may only be defined after the designation of neotypes and study of an appropriate number of populations using an integrative approach with conchological, anatomical and molecular characters. For now we consider this species according to its current concept (e. g., Horsák et al. 2020).

Allopeas clavulinum has been found in the tropical greenhouse of MUSE, where it is the commonest and most abundant achatinid species, and in the Biodiversity Garden (Botanical Garden of Padua), where it is rather uncommon. This is the first report from Italy.