Four new species of the genus Haplostoma (Haplostomatinae) are described on the basis of females living in compound ascidians from Madagascar. These copepods and ascidian hosts are as follows: 1) Haplostoma bispinosum, in Polyclinum ?macrophyllum Michaelsen; 2) H. elongatum, in P. diaphanum von Drasche; 3) H. madagascarensis, in P. ?insulsum Sluiter; and 4) H. junctum, in Eudistoma sp. In these copepods, the armature on the antenna and legs 1–4 exopods consists of bifurcate spines, representing the main primary diagnostic features of subgroup 2 of the genus. The four new species are distinguished from the three known species of subgroup 2 primarily by the armature formulas for legs 1–4 exopods and by the characters of the caudal rami. Haplostoma junctum, new species, is the only species of the genus whose caudal rami are medially fused. The diagnosis of subgroup 2 is revised on the basis of a comparative study of seven species (three previously known, four new).