The Ascetosporea are a group of protists that are parasites of animals, especially marine invertebrates. There are two groups, the haplosporids and paramyxids, which are not particularly similar morphologically but consistently group together on molecular trees, which place them near the base of the Cercozoa. Both produce spores without the complex structures found in similar groups (such as polar filaments or tubules). A 2009 study concluded that Haplosporidium species form a paraphyletic group and that the taxonomy of the haplosporidians needs a thorough revision.