Sea slug night fever: 39 new records of elusive heterobranchs in the western Mediterranean (Mollusca: Gastropoda) Author Salvador, Xavier 0000-0003-3039-7566 Author Fernández-Vilert, Robert 0000-0002-2812-4414 Author Moles, Juan 0000-0003-4511-4055 text Journal of Natural History 2022 2022-05-18 56 5 - 8 265 310 http://dx.doi.org/10.1080/00222933.2022.2040630 journal article 83506 10.1080/00222933.2022.2040630 38f6df24-838f-409a-90df-b56087e6a9bc 1464-5262 6758438 Aplysiopsis elegans Deshayes, 1853 ( Figure 5 (f)) Material examined Cova de l’infern ( Spain ), 42°19 ʹ 2.75”N , 3°19 ʹ 12.74”E , 19 November 2017 , 1.2 m depth , 5 spcs, adults and egg masses, L = 15–20 mm ; Cala Maset caves, Sant Feliu de Guíxols ( Spain ), 41°47 ʹ 10”N , 3°2 ʹ 44”E , 13 September 2019 , 1.3 m depth , 1 spc., adult, L = 15 mm ; Punta de la Mona , Andalucía ( Spain ), 36°43 ʹ 12.9”N 3°43 ʹ 43.1”W , 19 September 2020 , 3 m depth , 1 spc., adult and egg masses, L = 20 mm . External morphology Body elongate, narrow, background colour white with longitudinal dark red lines on dorsum and lateral body parts. Cerata long, smooth; background colour green with white punctuation, dark red vertical lines, pink on tips. Ecology Specimens were found feeding on the green alga Cladophora prolifera (Roth) Kützing, 1843 . The egg mass is whitish, cylindrical, found associated with algae. The specimen observed in 2019 was found at night crawling over algae, while the 2017 specimens were hidden inside algae. This could mean that slugs are mostly nocturnal, hiding among algae during the day. Distribution Greece ( OBIS 2021 ); Croatia ( Mavrič et al. 2014 ); Spain : Canary Islands ( Ortea et al. 1998 , 2001 ), Balearic Islands ( Ballesteros and Templado 1996 ), Catalonia (this study). Remarks This species is rarely observed. It is found among algae, especially Cystoseira , Cladophora and Halopteris scoparia (Linnaeus) Sauvageau, 1904 ( Mavrič et al. 2014 ), and probably feeds on them.