#2
are you sure about S. serratum? there are at least several other species of this group, some of which belong to Lekanesphaera, for instance S. hookeri, S. rugicauda, L. levi. See
www.marinespecies... for the complete checklist. Were is it from? S. serratum (and L. levi), should have strongly serrated uropods (these 2 long projections at both sides of the last abdominal segment) and to me they seem to have smooth edges. Your specimen is either Sphaeroma or Lekanesphaera, but I cannot establish the species. See also
http://www.aquati..._Galil.pdf for another alien Sphaeroma species recently established from israel (wit serrated edges)