Milax gagates (Draparnaud, 1801)

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

Milax gagates (Draparnaud, 1801)

Limax gagates Draparnaud, 1801, Tableau des mollusques terrestres et fluviatiles de la France: 100 [presumably near Montpellier fide Wiktor 1987: 202].

Type specimens.

Not investigated and probably do not exist; not mentioned by Wiktor (1987).

Swiss specimens examined.

NMBE 510286, Bern, Vechigen, in a garden, July 1970, leg. M. Wüthrich; other record: NMBE 561736, Jura, Porrentruy, in a garden, August 1985, leg. Rüetschi (specimen dried up).

Description.

Colouration. Wiktor (1987) describes M. gagates as uniformly greyish to blackish, except for the flanks being lighter and always lacking spots. However, our specimen from Vechigen has a beige basic colouration with grey-brown blurred dots covering the mantle and dorsal part of the slug. On the flanks, mainly the longitudinal tubercules are coloured by small brown dots, which results in a rather striped than reticulated appearance (Fig. 9A, B ).

The mantle has the same colouration as the dorsum. Above the pneumostome, along the horseshoe-shaped sinus groove, is a prominent grey band.

The neck and head have a darker colouration compared to the body and are uniformly grey coloured without dots.

The keel is also beige, but lighter coloured compared to the rest of the body.

According to Wiktor (1987), the sole varies from grey to blackish, with darker lateral zones and lighter central zone. In the Swiss specimen, the sole shows the same colour as the body, but small, brown-grey dots are spread over the whole sole with a strong accumulation in the central zone. Thus, it seems that the lateral zones are lighter if compared to the central one (see Fig. 9C ).

Mantle structure. The pneumostome is positioned slightly posteriorly to the centre of the mantle. The sinus groove is well visible in this preserved specimen.

Postpallial pocket organ. As described in T. rustica .

Integument structure. The tr are not countable, most likely because of the preservation of the specimen. The tubercules are large, similar to T. budapestensis , and not small as in T. nigra and T. rustica .

The keel is elevated over the neighbouring tubercules only close to the mantle, and flattens towards the posterior end.

Sole structure. The sole structure is like in the described Tandonia species (see T. rustica ), but instead of a uniform colouration, the sole is lighter on the lateral zones and more pigmented on the central zone.

Measurements. The measurements were done on the preserved specimen NMBE 510286. tl = 30.8 mm; sw = 4.1 mm; ml = 9.8 mm. This results in a ml/tl ratio of ~ 1/3.

Genital organs. Atrium short, spherical; accessory atrial glands are attached centrally to the atrium with several coiled tubules (Fig. 9E , arrow); inside the atrium, a short, pointed but flat stimulator (Fig. 9F , arrow) existing; penis rather long with a constriction in the middle; distal bulb containing penial papilla; penis retractor muscle attached at penis-epiphallus boundary; epiphallus tubular, widened distally; vas deferens entering asymmetrically on epiphallus.

Vagina shorter than penis; pedunculus broad and equal in length to vesicle; vesicle wider than pedunculus, spherical; female oviduct slender and long.

Spermatophore. The spermatophore was illustrated and described by Wiktor (1987: fig. 72).

Distribution.

This species is widespread in the western Palaearctic, in Portugal and parts of Spain, France, United Kingdom, etc. (see Wiktor 1987: map 3). Many of the existing populations are considered to be introductions; the original distribution remains unknown. Meanwhile, the species reached an almost global distribution.

Remarks.

The specimen from Vechigen is provisionally identified as M. gagates . The single animal depicted in Fig. 9 shows the general anatomical character states of this species; however, in our animal, the penis is considerably longer than in the specimen illustrated by Wiktor (1987: fig. 68). A comparison with all other Milax species yields no match; the only species, which might be present in the area is M. nigricans . This species differs by having a short epiphallus, and long tubules connecting the atrial glands with the atrium. Another potentially reliable distinctive character state can be found in the atrial stimulator: With only a few spines in M. gagates , and with lots of spines in M. nigricans (see Wiktor 1987; Hutchinson and Reise 2013). However, the stimulator in our specimen was completely reduced and no detailed structures were discernible. Unfortunately, no DNA could be extracted from the rather old specimen from Vechigen.

The very small specimen from Porrentruy was not only completely dried up and completely bleached but turned out to be a young juvenile without any sign of a genital pore. In fact, juvenile specimens cannot be determined on species level from exterior characters, when genital anatomy is not developed. For this reason, we suggest considering this record as Milax sp. rather than M. gagates .

Finally, there is a specimen housed in the collection of the Muséum d’histoire naturelle de la Ville de Genève, which had been identified as M. gagates (MHNG-MOLL-138933, Geneva, November 1968). The specimen was already dissected prior to our investigation and damaged. The investigation of its genital organs yielded no definite result on its specific identity; it certainly is a species from the Milacidae .

Figures

Figure 9. Anatomy of Milax gagates. A-F NMBE 510286 A lateral view right B dorsal view C ventral view D situs of genitalia E accessory atrial glands attached with coiled tubules on atrium F stimulator inside the atrium. Abbreviations: a = atrium; ag = atrial gland; bc = bursa copulatrix; ep = epiphallus; fod = free oviduct; p = penis; ped = pedunculus; prm = penis retractor muscle; spo = spermoviduct; stim = stimulator; v = vagina; vd = vas deferens.