Muangnua Solem, 1966

Tumpeesuwan, Chanidaporn & Tumpeesuwan, Sakboworn, 2019, Muangnua arborea, a new semislug (Gastropoda, Stylommatophora, Helicarionidae, Durgellininae) from Loei Province, northeastern Thailand, ZooKeys 894, pp. 19-32 : 19

Genus Muangnua Solem, 1966

Type species.

Muangnua limax Solem, 1966.

Diagnosis

(based on type material studied by Solem (1966)). Shell reduced, having only one remnant of coiling, which in living semislug is completely covered by fused shell laps. Mantle lobes form large cephalic shield reaching base of tentacles. Tail long and slender, with hooked caudal horn. Posterior visceral hump rounded, resting in V-shaped body groove. Jaw thin, without median projection or sculpture. Radula possesses tricuspid central, lateral, and marginal teeth. Genitalia, was studied from juvenile specimen, therefore, epiphallus cannot be differentiated. Free oviduct short, vagina rather long, dart apparatus, and other accessory penial organs absent; gametolytic sac (= spermatheca in Solem, 1966) long, finger-like, reaching two-thirds of way to albumen gland; atrium rather short.

Remarks.

The genus Muangnua was originally placed in the family Helicarionidae and tribe Durgelli by Solem (1966), after which Vaught (1989) moved it to the family Ariophantidae (Table 1 ). Panha (1996), Hemmen and Hemmen (2001), and Nabhitabhata (2009) followed Vaught’s classification. Schileyko (2002) also follows Vaught (1989), but he placed genus Muangnua into the subfamily Ariophantinae and tribe Ariophantini (Table 1 ). Recently, Bouchet and Rocroi (2005) and Bouchet et al. (2017) moved the tribe Durgellini into the subfamily Durgellinae ( Helicarionidae ). In this study, we followed Bouchet and Rocroi’s classification. Among the three genera of long elongate, small Southeast Asian semislugs ( Parmarion P. Fischer, 1856; Muangnua Solem, 1966; and Laocaia Kuzminykh, 1999), their external morphology is very similar, but they possess many different characters. Parmarion frequently covers their ear-shaped shell with a mantle lobe, whereas Muangnua and Laocaia always cover their finger nail-shaped shell and triangular shaped shell, respectively, with their mantle lobe. The caudal horn overhangs in Muangnua and Laocaia but does not overhang in Parmarion . The postero-dorsal midline keel is present in Parmarion and Muangnua whereas it is present or absent in Laocaia .