Specific diagnostic characters are reviewed and redefined for the genusPolymastiain northern New Zealand waters, to provide a framework for the recognition of new species, and for the revision and redefinition of other Polymastiidae. Eight new species ofPolymastiaare described, andPolymastia fuscaBergquist,P. hirsutaBerquist, andP.cf.massilisCarter are redescribed in the light of new material. Species ofPolymastiawhich contain exotyles and centrotylote oxea in addition to the usual megasclere complement, provided the opportunity to redefine the polymastid generaProteleia, andTylexocladus, which would typically have been reserved respectively, for sponges with these spicules. Anew species ofTylexocladusis described from the Chatham Rise in southern New Zealand, providing a first record of the genus from this location. A new genusAcanthopolymastiais established for southern ocean Polymastiidae with acanthose centrotylote oxea, withAtergia acanthoxaKoltun from Antarctica as the type species. Two additional species from New Zealand and the Norfolk Ridge, New Caledonia are described, and all are compared to Atlantic species of the same genera. Suggestions for partitioning of shallow‐waterPolymastiaspecies are put forward.