1. Acentrella Bengtsson, 1912

Diagnosis.

1) Very reduced paracercus; 2) stocky mouthparts; 3) head compressed dorsoventrally; 4) presence of a complete row of long thin setae on the dorsal margin of tibia; 5) villopore present on the ventral margin of fore femora.

Remarks.

In the past, Acentrella was considered as a subgenus of Baetis ( Müller-Liebenau 1969). Confusions with species with reduced paracercus ( Baetis pavidus or the subgenus Baetis Patites) can be avoided by the examination of the mouthparts, especially of the mandibles as well as the distal margin of the tergites. The abdominal tergites also present a characteristic dark brown pattern (Fig. 3A).

Two species of Acentrella are reported in the Maghreb: Acentrella cf. sinaica Bogoescu, 1931 and Acentrella almohades Alba-Tercedor & El-Alami, 1999. Acentrella sinaica was originally described from Romania, then reported from several countries from Central and South Europe. This species is not abundant but widely distributed in North Algeria and North-West Tunisia. Maghrebian populations seem morphologically very similar to those from central Europe. However, molecular preliminary results suggest that the Maghreb populations most probably belong to a new undescribed species (Benhadji et al. 2020). Acentrella almohades is originally described from the Rif mountains and middle Atlas as well as from south-west of Spain. The two species do not seem to co-occur. They can be separated by the length of the setae of the dorsal margin of femora (longer in A. cf. sinaica than in A. almohades) and the number of regular rows of stout setae at apex of paraglossa (three rows in A. cf. sinaica, four rows in A. almohades) (Alba-Tercedor and El-Alami 1999).