Eight new species belonging to the family Porcellidiidae (Harpacticoida: Copepoda) are described from the southern coast of New South Wales, Australia. All live on the surface of seaweeds in the eulittoral and sublittoral zones. Characteristic features of the family are described and redefined. The genus Porcellidium is redefined and subdivided into three groups on the setation of the female caudal ramus and structure of the male antennule. Four of the new species, Porcellidium hormosirii, P. ocellum, P. pulchrum and P. erythrogastrum have been assigned to the "Hormosirii" group, and P. naviculum and P. phyllosporum to the "Naviculum" group. A new genus, Acutiramus, is defined and two new species, A. rufolineatus and A. quinquelineatus, assigned to it. The relationship between the new species and previously described species of Porcellidium is discussed. Porcellidium viride (Phillipi, 1840) and P. sarsi (Claus, 1863) are placed in the 'Naviculum' subgroup, P. rubrum Pallares, 1966, P. hartmannorum Tiemann, 1978, P. erythrum Hicks, 1971 and P. algoense Hicks, 1982 are placed in the subgroup 'Hormosirii', and P. fimbriatum Claus, 1889 is placed in a subgroup of its own. Porcellidium acuticaudatum Thompson & Scott, 1903, P. brevicaudatum Thompson & Scott, 1903 and P. ovale Geddes, 1968 (not Haller) have been placed in the new genus Acutiramus.