Limacus

There remains a difference of opinion whether Limacus should be its own genus or a subgenus of Limax. A 2026 molecular phylogeny^[3] indicated that Limacus and Limax form sister clades (forming a polytomy together with Turcomilax), so both treatments are equally valid. Formerly, if Limacus was considered a subgenus of Limax, Limacus maculatus had to be known as Limax ecarinatus (because another species was formerly known under the name Limax maculatus),^[4] but a ruling by the ICZN has now made Limax maculatus correct.^[5]

Two extant species are known and one fossil.

• Limacus flavus (Linnaeus, 1758), the type species;^[6] synonyms = Limax flavus Linnaeus, 1758; Limacus breckworthianus Lehmann, 1864
• Limacus maculatus (Kaleniczenko [uk], 1851); synonyms = Limax maculatus (Kaleniczenko, 1851), Limax ecarinatus Boettger, 1881; Limax grossui Lupu, 1970; Limax pseudoflavus Evans, 1978
• † Limacus crassitesta (Reuss, 1868)

The two extant species are hard or impossible to distinguish on external characters, so identification relies on a character of the genital anatomy, requiring dissection. They are large slugs up to 130 mm long, yellowish with mottled darker markings and blue-grey tentacles.^[8] Like other limacid slugs they have a pointed tail, and the pneumostome is in the hind part of the mantle. Genetic information suggests that the species may hybridise.^[9] Both species have spread from their native ranges in South-eastern Europe and Asia, with L. flavus occurring worldwide as a synanthrope.^[10][11]