Key to species of Syllidia de Quatrefages, 1865

1 Body with longitudinal, ventral dark brown band; without dorsal pigmentation.................................... 2

– Body without ventral pigmentation, anterior segments with a transverse black line; jaw outer projection markedly longer than inner one, without median projection...................................... S. liniata Hartmann-Schröder, 1962 Peru

2(1) Jaw outer and inner projections of about the same length, without median projection................................ 3

– Jaw outer projection markedly longer than inner projection, dark brown, with a median rounded projection................................................................. S. hongkongensis Ruta & Pleijel, 2006 Hong Kong and Hawaii

3(2) Jaw denticulate margin distinct, outer projection not reaching denticulate margin; inner projection tapered into a blunt tip........................................................................ S. armata de Quatrefages, 1866 France

– Jaw denticulate margin indistinct, outer projection reaching denticulate margin; inner projection slightly tapered to an acute tip............................................................................... S. amaralae n. sp. S Brazil