Figs 5–24. Variability of the ligula within and between morphotypes of A. ater s.l. (5–10 – FR; 11–15 BR; 16–21 – AR) and A. vulgaris (22–24). Figures on the left show schematic views of the atrium, indicating the intra-morphotype range of configurations of the ligula base on the inside of the atrium: each variant configuration is distinguished by a different pattern of hatching or spotting. The ridge on the inside of the atrium is indicated with a dashed line and the site of attachment of the retractor muscle with horizontal hatching. Figures on the right show the range of shapes of the flattened-out ligula (viewed from the inside), distinguishing the base (attached to the atrium or oviduct wall) from the surrounding free-hanging flange. In the FR and BR morphotypes of A. ater s.l. a spongy funnel-shaped area of the ligula is shown; at the tip of the funnel is the oviduct opening, but this is often difficult to discern. In the AR morphotype the opening of the oviduct is usually instead surrounded by a circular swelling, and the opening is more apparent (Figs 19–21). Abbreviations: ovo – oviduct opening, lbrf – ligula base, right flank, lblf – ligula base, left flank

Published as part of Reise, Heike, Schwarzer, Anne-Katrin, Hutchinson, John M. C. & Schlitt, Bettina, 2020, Genital morphology differentiates three subspecies of the terrestrial slug Arion ater (Linnæus, 1758) s.l. and reveals a continuum of intermediates with the invasive A. vulgaris Moquin-Tandon, 1855, pp. 1-34 in Folia Malacologica 28 (1) on page 11, DOI: 10.12657/folmal.028.001, http://zenodo.org/record/4615365