Two species of marine actinosporeans with spores that develop in groups of four rather than eight within a pansporocyst are described. In other respects, including triradial symmetry, three polar capsules each enclosing a coiled polar filament, parasitic in invertebrates, they conform with other actinosporeans. Both new species were found in the coelom of tubificid oligochaetes collected from Moreton Bay, Queensland, Australia. Spores of Tetraspora discoidea n.g. n.sp. are disc-like, almost round in apical view and dorso-ventrally compressed in side view, whereas spores of Tetraspora rotundum n.sp. are spherical. The novel development of these two marine actinosporeans may signify other variations in the life-cycles of marine Myxozoa.