Tandonia budapestensis (Hazay, 1880)

Schallenberg, Vivianne M., Heim, Rene, Schneppat, Ulrich E., Mueller, Peter, Rueetschi, Joerg & Neubert, Eike, 2022, Revision of the family Milacidae from Switzerland (Mollusca, Eupulmonata, Parmacelloidea), ZooKeys 1116, pp. 149-179 : 149

Tandonia budapestensis (Hazay, 1880)

Figs 6 , 7E, F

Tandonia budapestensis Amalia Tandonia budapestensis Hazay, 1880, Malakozoologische Blätter, Neue Folge. 3: 37, pl. 1, fig. 1 [Budapest, Festungsberg im königlichen Garten].

Type specimens.

Not researched and not mentioned by Wiktor (1987); probably lost.

Diagnosis.

Sole with a dark central field; for other character states, refer to the paragraph under T. rustica .

Description.

Colouration. Living Swiss specimens (n = 10) show a dark rusty-brown to dark chocolate-brown colour on dorsum and flanks to the fringe of the sole. The flanks below the mantle are somewhat paler dark brown grey. Dorsum and flanks, if not unicolourous, may show small black spots and stripes concentrated along the tubercle groves. This can be observed only under magnification and in good light.

The mantle sometimes can be darker than the dorsum because of many black dots and irregular black marbling.

The ommatophores are almost black-brown, but sometimes little translucent in good light, so the black ommatophoran retractor can be seen through the integument. The tentacles are of the same colour.

The colour of the keel ranges from dark brown to rusty orange in its full length.

The sole is grey to dark blackish grey, with the central field sometimes being almost black. In all three sole fields, many black, irregularly jagged spots (chromatophores?) exist, which can be seen only under magnification.

Mantle structures. The pneumostome is positioned on the right side of the body at 2/3 of mantle length, well posteriorly of the middle of the mantle.

Postpallial pocket organ. As in Tandonia rustica .

Integument structures. The number of tr on the integument, counted from the slit of pneumostome to the keel (n = 7; tr 9/10-tr 12, ø tr 10/11). The low number of tr allows in almost all cases to differentiate T. budapestensis from small and dark T. rustica . Wiktor (1987) found 9-11 tr, which fits to the variation we found in Swiss specimens. The surface texture and the width of tubercles in live specimens vary somewhat depending on their position on the body. The tr are all more or less finely crenulated. Caused by the low number of tr, they are comparatively wide and obviously wider then in T. rustica . All tr are divided in several compartments.

In all specimens, the keel extends from the posterior margin of the mantle to the end of the dorsum. It is not projecting but evenly rounded, sometimes almost flat and not much exposed over the dorsal tr. It is entirely smooth.

Sole structure. The sole structure is similar as in Tandonia rustica , but the colouration is not uniform and has a dark central field.

Measurements. lw (n = 8): 0.4-1.28 g; ø 0.78 g; tl (n = 8): 24.6-62 mm, ø 40 mm; ml (n = 8): 7-19 mm, ø 12 mm; sw (n = 8): 2.5-6 mm, ø 3.7 mm.

Ratio of tl/ml ranges from 24/7 mm to ca. 62/19 mm; ø ml is little more than 1/3 of tl.

Mucus. The mucus lacks any pigmentation on body, mantle and sole, but is extremely sticky. In a few cases mucus of little pale-orange colour may occur in Swiss specimens.

Genital organs. Atrium wide, spherical shaped; atrium wall covered with folds; penis bulged in the centre; penial walls with long folds ending at muscular ring; penis papilla large, simple oval fold around the opening; papilla basis long, distally shrinking in diameter; penis/epiphallus boundary marked with constriction, where penis retractor muscle inserts; epiphallus matching penis in length; epiphallus surface smooth with apical part kinked.

The vagina is extremely short, separated from the atrium by a muscular ring; accessory glands sac-like attached at centre of the vagina; vaginal walls simple; pedunculus of bursa copulatrix large in diameter, longish vesicle; pedunculus wall with longitudinal internal folds showing a zig zag pattern; oviduct slim and long.

Spermatophore. The spermatophore was described and illustrated by Wiktor (1987: figs 114, 115).

Distribution.

Tandonia budapestensis is an introduced species and not commonly found in Switzerland. Our series are small (n = 10), and all originate from Cantons Bern, Lucerne, and Zurich. It is rather strictly nocturnal, but occasionally occurs under very wet weather conditions also during the day (pers. obs.). It is a quite inconspicuous slug, and thus only rarely found. The relatively few records at CSCF hardly reflect the state of occurrence in the country, and it is assumed that the species is widely overlooked by Swiss malacologists. It is apparently a lowland species and has not yet reached higher altitudes. This coincides with observations on this species in Bulgaria.

Habitat.

All Swiss specimen were exclusively found in urban areas (anthropogenic habitats) in house gardens, along an old city wall, and close to a small brook with trees and shrubs. The population along the old city wall of Lucerne was checked several times over the years and seems to be stable.

Remarks.

We found some Bulgarian specimens ranging from unicoloured yellow to almost completely black. Such colour morphs might be expected in the future in Switzerland, too.

Figures

Figure 6. Tandonia budapestensis. Sequenced specimen NMBE 564562, Zurich, Wollishofen. A lateral right view B ventral view C situs of genitalia D distal genitalia opened to show inner structures E opened penis papilla and epiphallus F penial papilla. Abbreviations: a = atrium; bc = bursa copulatrix; ep = epiphallus; fod = free oviduct; p = penis; ped = pedunculus; prm = penis retractor muscle; spo = spermoviduct; v = vagina; vd = vas deferens; vg = vaginal gland.

Figure 7. Living specimens of Tandonia. A, B Tandonia rustica A sequenced specimen NMBE 568974, Wartau, Truebbach B sequenced specimen NMBE 568973, Rovio, Sovaglia C, D Tandonia rustica (two mottled specimens) meeting a pale colour morph specimen of Tandonia nigra, Val Cuerta, Mt. Generoso E, F Tandonia budapestensis E NMBE 571881, Roggwil, F NMBE 571882, Meggen.