Ariunculus

Only two species are currently recognised:^[7]

subgenus Ariuncululus

• Ariunculus speziae Lessona, 1881^[1] – type species of the genus; Italian Alps^[8] with one record in Switzerland^[9]

subgenus Ichnusarion Pollonera, 1890^[6]

• Ariunculus isselii Lessona & Pollonera, 1882^[10] – Sardinia

Other species have been discounted as distinct members of the genus:^[7]

• A. mortilleti and A. camerani are considered synonyms of A. speziae (all three were originally described in the same article,^[1] but differ only in size and coloration, not genitalia);^[8]
• A. moreleti is considered a species of Letourneuxia;^[11]
• A. pallaryi matches Letourneuxia numidica in its description;^[7]
• A. austriacus has been synonymised with Arion subfuscus;^[12]
• A. tricolor and A. nigratus are thought to have been misidentified juveniles of a large Arion;^[11]
• A. ischii was apparently a misprint for A. isselii.^[7]

Genital characters that have been proposed as diagnostic of the genus are:

• the genital pore is very anterior, anterior to the pneumostome;^[10]
• the atrium is large;^[10]
• the duct of the bursa copulatrix opens near the end of the epiphallus;^[10]
• the oviduct is long with two bends;^[13][14]
• the epiphallus blends imperceptibly with the vas deferens;^[10]

At least in one species of Ariunculus, this last character reflects that sperm is transferred naked rather than in a spermatophore formed in the epiphallus; this is a fundamental contrast with Arion and Geomalacus.^[7]

Ariunculus differs from Geomalacus, and is similar to Arion, in that the caudal gland is prominent and the mantle contains only calcareous granules rather than a shell plate.^[6]