Ariunculus

''Ariunculus'' is a genus of air-breathing land slugs in the family Arionidae, the roundback slugs. Sometimes it has been considered as a subgenus of ''Arion'', and sometimes the subgenus ''Ichnusarion'' has been raised to generic rank.

Etymology

The stem of ''Arion'' plus the suffix -unculus, which is a diminutive in Latin. Hence "little ''Arion''". Pollonera justifies why "Ariunculus" is appropriate rather than "Arionculus" (cf. "homo" and "homunculus").

The subgenus name ''Ichnusarion'' is also based on "''Arion''", to which has been added "Ichnusa", a Latin name of Sardinia, where the single species of this subgenus is endemic.

Species

Only two species are currently recognised:

subgenus ''Ariuncululus''
* '' Ariunculus speziae'' Lessona, 1881 – type species of the genus; Italian Alps with one record in Switzerland
subgenus ''Ichnusarion'' Pollonera, 1890
* '' Ariunculus isselii'' Lessona & Pollonera, 1882 – Sardinia

Other species have been discounted as distinct members of the genus:
* ''A. mortilleti'' and ''A. camerani'' are considered synonyms of ''A. speziae'' (all three were originally described in the same article, but differ only in size and coloration, not genitalia);
* ''A. moreleti'' is considered a species of '' Letourneuxia'';
* ''A. pallaryi'' matches ''Letourneuxia numidica'' in its description;
* ''A. austriacus'' has been synonymised with '' Arion subfuscus'';
* ''A. tricolor'' and ''A. nigratus'' are thought to have been misidentified juveniles of a large ''Arion'';
* ''A. ischii'' was apparently a misprint for ''A. isselii''.

Diagnostic characters

Genital characters that have been proposed as diagnostic of the genus are:
* the genital pore is very anterior, anterior to the pneumostome;
* the atrium is large;
* the duct of the bursa copulatrix opens near the end of the epiphallus;
* the oviduct is long with two bends;
* the epiphallus blends imperceptibly with the vas deferens;
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''.

''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.

References

{{DEFAULTSORT:Ariunculus (Genus)
Arionidae
Gastropod genera