Botryllophilus symmetricus is described on the basis of females living in a compound ascidian (Synoicum), collected in Madagascar. The new botryllophiline belongs to female morphotype B of the genus (urosome with more than 5 segments) and is distinguished from the five congeners of type B by the following characters: 1) body fusiform symmetrical, elongated metasome weakly 5-segmented, and short urosome 8-segmented; 2) right and left legs 1–4 (asymmetrical in morphology) symmetrically placed, with equally wide space between 2 legs on each segment, right leg exopods unimerous subrectangular; and 3) ventral anal segment lacking ornamentation. The new copepod is the only representative of morphotype B in Botryllophilus of the Humes collection in Madagascar (1963).