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,[2][3][4] and sometimes the subgenus Ichnusarion has been raised to generic rank.[5]

Ariunculus
A live individual of Ariunculus speziae, coin diameter is 16.25 mm
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Subclass: Heterobranchia
Superorder: Eupulmonata
Order: Stylommatophora
Family: Arionidae
Genus: Ariunculus
Lessona, 1881[1]
Type species
Ariunculus speziae
Lessona, 1881
Diversity
2 species, each in its own subgenus

Etymology

The stem of Arion plus the suffix -unculus, which is a diminutive in Latin. Hence "little Arion". Pollonera[6] 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:[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]

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]

Diagnostic characters

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]

References
  1. Lessona, M. (1881). "Sugli Arion del Piemonte". Atti della Reale Accademia delle Scienze di Torino. 16: 185–197 + 1 plate.
  2. Heynemann, D.F. (1905). "Die geographische Verbreitung der Nacktschnecken". Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft. 30: 1–92 + 2 plates. doi:10.5962/bhl.title.46556.
  3. Ehrmann, P. (1956). "Vol. 2.(1). Kreis: Weichtiere, Mollusca". In Brohmer P.; Ehrmann P.; Ulmer G. (eds.). Die Tierwelt Mitteleuropas. Leipzig: Quelle & Meyer. pp. 1–264 + plates 1–13.
  4. Welter-Schultes, F.W. (2012). European non-marine molluscs, a guide for species identification. Göttingen: Planet Poster Editions. ISBN 978-3-933922-75-5.
  5. Schileyko, A.A. "Treatise on Recent terrestrial pulmonate molluscs. Part 15: Oopeltidae, Anadenidae, Arionidae, Philomycidae, Succineidae, Athoracophoridae". Ruthenica. Suppl. 2: 2049–2210.
  6. Pollonera, C. (1890). "Recensement des Arionidae de la Région Paléarctique". Bollettino dei Musei di Zoologia ed Anatomia Comparata della Reale Università di Torino. 5 (87): 1–42.
  7. Hutchinson, J.M.C.; Reise, H. (2015). "Mating in Ariunculus isselii, an arionid slug without a spermatophore". Journal of Molluscan Studies. 81 (2): 247–258. doi:10.1093/mollus/eyu086.
  8. Bishop, M.J. (1976). "I molluschi terrestri della provincia di Novara". Atti della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano. 117: 265–299.
  9. Rüetschi, J.; Stucki, P.; Müller, P.; Vicentini, H.; Claude, F. (2012). Rote Liste Weichtiere (Schnecken und Muscheln). Gefährdete Arten der Schweiz, Stand 2010. Neuenburg: Bundesamt für Umwelt, Bern, and Schweizer Zentrum für die Kartografie der Fauna.
  10. Lessona, M.; Pollonera C. (1882). Monografia dei limacidi italiani. Turin: Ermanno Loescher. doi:10.5962/bhl.title.10743.
  11. Castillejo, J.; Rodríguez, T. (1991). Babosas de la Península Ibérica y Baleares: inventario crítico, citas y mapas de distributión (Gastropoda, Pulmonata, Terrestria nuda). Monografías da Universidade de Santiago de Compostela no. 162 (PDF). Santiago de Compostela: Universidade de Santiago de Compostela, Servicio de Publicacións e Intercambio Científico.
  12. Reischütz, P.L. (1980). "Ariunculus austriacus Babor synonym zu Arion (Mesarion) subfuscus (Drapanaud)". Mitteilungen der zoologischen Gesellschaft Braunau. 3: 297–298.
  13. Germain, L. (1930). Faune de France, Vol. 21: Mollusques terrestres et fluviatiles. Part 1 (PDF). Paris: Lechavalier.
  14. Platts, E.A.; Speight, M.C.D. (1988). "The taxonomy and distribution of the Kerry slug Geomalacus maculosus Allman, 1843 (Mollusca: Arionidae) with a discussion of its status as a threatened species". Irish Naturalists' Journal. 22 (10): 417–430. JSTOR 25539243.
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