A large inventory of tanaidaceans is reported from an upstream-downstream transect in tidal channels of the Gulf of Gabès (Tunisia), collected during a 2016–2017 seasonal sampling campaign. Eight species were identified from a collection of 2,896 individuals, including four species of the genus Apseudopsis. One species belonging to Apseudopsis has recently been described from this material, while four other species are newly recorded from Tunisian waters. Most of the individuals were sampled in Winter and from a single channel polluted by the release of phosphogypsum waste. This unusually high diversity in shallow waters is discussed from a taxonomic point of view, taking into account the misidentification of the species Apseudopsis latreillii, which is the only species of the genus mentioned in the most widely used identification keys. Most of the reports on the geographical distribution of this species need to be re-assessed taking into account the species described recently in the North Atlantic Ocean including the Mediterranean Sea.