Monstrilla mahahualensis sp. nov., holotype adult male from Mahahual, Mexico A cephalic region showing weak reticulation pattern, dorsal view B perioral area showing oral cone (oc), cuticular processes and ornamentation, ventral view C antennule segments 2 and 3 showing setation pattern and position of integumental structure D urosome showing fifth legs and genital complex, lateral view E third and fourth antennule segments showing setation pattern and position of integumental structure (is) F fourth and fifth antennule segments showing setation pattern and position of integumental structure G fifth antennule segment showing setation pattern Scale bars: 50 μm (A–G).