Abstract
Heterobranch gastropods, particularly Nudibranchia, are commonly known as sea slugs and often used for marine biodiversity assessments important for monitoring habitat health and ensuring ecosystem functions. In the Mediterranean, nudibranch species are predominantly reported from the European coast and only occasionally from the North African coast, leaving incomplete knowledge of Mediterranean nudibranch diversity and distribution. To address this sampling bias and knowledge gap, the results of a six-year biodiversity assessment project on Nudibranchia in Libyan waters are presented, with a focus on a survey area off the coast of Tripoli. The documented nudibranchs included one non-indigenous species and 17 native species belonging to 11 families: Felimare cf. orsinii (Vérany, 1846), Felimare villafranca (Risso, 1818), Felimida binza (Ev. Marcus & Er. Marcus, 1963), Felimida krohni (Vérany, 1846), Atalodoris sp., Dendrodoris grandiflora (Rapp, 1827), 1880, Berghia verrucicornis (Costa, 1867), Cratena peregrina (Gmelin, 1791), Favorinus branchialis (Rathke, 1806), Limenandra nodosa Haefelfinger & Stamm, 1958, Spurilla neapolitana (Delle Chiaje, 1841), Hancockia uncinata (Hesse, 1872), Calmella cavolini (Vérany, 1846), Edmundsella pedata (Montagu, 1816), Trinchesia sp., and Marionia blainvillea (Risso,1818). Polycerella emertoni A. E. Verrill, 1880 was the only non-indigenous species. Additionally, our study offers initial insights into habitat preferences, seasonal distribution, breeding periods, and identification traits for Nudibranchia from the understudied Mediterranean coast of Africa and provides a baseline for future studies of changing marine communities.