Key to species of Isaea Milne Edwards, 1830

1 Accessory flagellum with 3–6 articles, carpus of gnathopod 2 long (0.50–0.65 times length of propodus) ............................................................................... 2

—— Accessory flagellum with 2 articles, carpus of gnathopod 2 short (0.15–0.25 times length of propodus) ....................................................................................... 3

2 Eyes very large; epimeral plate 3 with posterodistal tooth, posterior margin almost straight ................................................................................ I. montagui

—— Eyes medium-sized; epimeral plate 3 bearing minute posterodistal tooth with inset setule, posterior margin convex .............................................. I. elmhirsti

3 Antennae slender, with long setae on posterior margins, basis of pereopod 5 subrectangular ......................................................................................... I. concinna

—— Antennae relatively stout, with short setae on posterior margins, basis of pereopod 5 oval ........................................................................ I. concinnoides sp. nov.