(Fig. 2 f)
Habitat. 10 specimens were collected from oyster beds.
Locality. Bizerta lagoon (37° 13' 19.29" N; 9° 55' 49.94" E), lagoon of Tunis (36° 48' 23.53" N; 10° 16' 04.63" E).
Localities in Tunisia from bibliography. Bizerta lagoon (Gammoudi et al. 2011; Gammoudi & Tekaya 2012). Other localities in the world. Sicily (Blanchard 1847); Gulf of Naples (Lang 1884); the coast of Catalonia (Novell 2001); Mauritania (Palombi 1939); North Atlantic (Noreña et al. 2015).
Remark. The polyclad Discocelis tigrina was found usually in association with the cultivated oyster Crassostrea gigas (Thunberg, 1793) in Bizerta lagoon. In some cases, the flatworm was collected inside empty shells or shells containing a rest of bivalve viscera suggesting a likely predator-prey association. This hypothesis is supported by the fact that many acotyleans are known to be predators of commercial bivalves (Galleni et al. 1980; Gammoudi et al. 2016a).