Morphological diagnostic characters used to discriminate the 11 species of Oncaeidae present in the Gulf of Naples (*measured using traditional method).

The species investigated in the present work are indicated in bold. List of characters [11]: 1 = body size ≥ 1mm; 2 = body size 1mm; 3 = exoskeleton moderately chitinised; 4 = exoskeleton heavily chitinised; 5 = leg 4 endopod with distal conical process; 6 = leg 4 endopod without distal conical process; 7 = prosome with conspicuous dorso-posterior projection in lateral view; 8 = prosome without conspicuous dorso-posterior projection in lateral view; 9 = prosome to urosome ratio; 10 = genital double-somite length to width ratio; 11 = anal somite length to width ratio; 12 = caudal ramus length to width ratio.