Monstrilla mahahualensis sp. nov., SEM-prepared adult male from Mahahual, Mexico A antennules, ventral view indicating purported segments 3–5 B same, semi- lateral view indicating purported segments 1–5 C detail of wrinkled cuticular field on perioral surface, ventral view D purported fourth antennulary segment showing setation pattern and second integumental structure (is2) E legs 1–3 showing endopodal and exopodal rami general setation pattern, arrows indicate relatively long outer exopodal spines, ventral view F urosome with fifth legs armed with long setae, and genital complex, ventral view. Setal elements on antennule segments 1–4 labeled following Grygier and Ohtsuka’s (1995) nomenclature.