A new deep-sea species of Ambilimbus nom. nov. (Copepoda, Cyclopoida, Erebonasteridae) is described from the Mid-Atlantic Ridge (hydrothermal vent site Rainbow, 36°13'N 33°54'W, depth 2285 m). This is the first record for the family Erebonasteridae Humes, 1987 from the Mid-Atlantic Ridge. Ambilimbus nom. nov. is here proposed as a replacement name for Amphicrossus Huys, 1991, as the latter is preoccupied by Amphicrossus Erichson, 1843 (Insecta, Coleoptera). The new species, Ambilimbus arcuscelestis, is similar to A. pacificus (Huys, 1991) comb. nov. and A. tuerkayi (Martínez Arbizu, 1999) comb. nov. in having the third exopodal segments of legs 1 and 2 armed with four and five inner setae, respectively (instead of three and four inner setae as in A. spinulosus (Humes, 1989) comb. nov. and A. altalis (Humes & Huys, 1992) comb. nov.). It differs from its four congeners by the lack of the inner coxal seta on leg 3. This character and the mid-ventral processes located between the intercoxal sclerites of legs 1–4 are presumed to be apomorphies of the new species.