Deroceras riedelianum Wiktor, 1983 Fig. 62 Deroceras riedelianum – Wiktor 1983 a: 162–164, figs 14–21 – Algeria: Skikda (= Philippeville); Djebel Edough near Annaba (= Bône) between Seraïdi (= Bugeaud) and Sainte-Croix-d’Edough; Annaba (= Bône) ruins of Roman town Hippona; between Skikda (= Philippeville) and Stora. Wiktor 2000: 368, 393, 500, 502, 511–512, 518–519, 580–582 figs 581–588 – Algeria: Skikda (= Philippeville) and Annaba (= Bône). Material examined. No specimens in our samples. Diagnosis. Body length ≤ 23 mm. Colouration pale coffee with dark spotting on the mantle and posterior body. Mantle is attached distally, allowing its anterior portion to be bent upward at ~ 2 / 3 of its length. Elongated penis, medially constricted; enlarged distal part; proximal part equipped with one smooth process which probably constitutes the penial gland; on the opposite side, there is an appendix-like distension. The vas deferens opens laterally between the process and the distension. The musculus retractor penis is attached between the process and the distension, but apically. The stimulator is cone-shaped, connected with a big fold running toward the proximal penis. Distribution. So far, known only from the type locality: surroundings of Skikda and Annaba (northwestern Algeria). Ecology. This species has been found in brushwood, cork oak forests, ruins, and rock piles; it takes refuge in wet litter and under tree trunks (Wiktor 2000). Remarks. Bourguignat (1862 b) described Limax subsaxanus as characterised by a stocky anterior body and a sharp and slender back, pink body, and white foot, similar to the genus Krynickia (= Krynickillus (Agriolimacidae)) due to the mantle being large and much detached in its anterior portion. The description in Bourguignat (1861) and the figure of the shell and body in Bourguignat (1864: pl. 3, figs 13–16) allow us to attribute L. subsaxanus to the genus Deroceras. Deroceras subsaxanum, described from Constantina (ca 85 km southwest of Annaba and Stora), may be a senior synonym for D. riedelianum. However, the relationship of D. subsaxanum to both D. riedelianum and D. cf. brondelianum can only be clarified by the study of topotypical specimens. Castillejo (1996, 1997) and Borredà and Martínez-Ortí (2017, 2022) considered D. riedelianum a junior synonym of D. ponsonbyi (Hesse, 1884). Following Wiktor (2000), we disagree with this view: Wiktor (2000) highlighted that D. ponsonbyi has a bifurcated penial retractor muscle, with one insertion in the distal penis and the other one in the proximal penis, while D. riedelianum has only one insertion in the proximal penis; secondly, the penial appendix appears different in the two species. In addition, D. ponsonbyi shows glandular tissue covering the distal penis distention (absent in D. riedelianum). We regard D. ponsonbyi, known from the Gibraltar area, as an endemic species to southern Spain and D. riedelianum as endemic to northeastern Algeria (Kabylia). The Deroceras species recorded (under D. agreste) by several nineteenth-century authors in western Algeria (Oran) and northern Morocco require further research (Terver 1839; Morelet 1853; Hesse 1884; Heynemann 1885; Pollonera 1891).

Published as part of Ramdini, Ramdane, Liberto, Fabio, Sadouk, Ghania, Gregorini, Armando & Colomba, Mariastella, 2026, Contributions to the knowledge of slugs and semi-slugs (Gastropoda, Pulmonata, Stylommatophora) from Algeria, pp. 307-348 in ZooKeys 1270 on pages 307-348, DOI: 10.3897/zookeys.1270.156458