Cercozoa: A group of amoeboid and flagellate EUKARYOTES in the supergroup RHIZARIA. They feed by means of threadlike pseudopods.Eukaryota: One of the three domains of life (the others being BACTERIA and ARCHAEA), also called Eukarya. These are organisms whose cells are enclosed in membranes and possess a nucleus. They comprise almost all multicellular and many unicellular organisms, and are traditionally divided into groups (sometimes called kingdoms) including ANIMALS; PLANTS; FUNGI; and various algae and other taxa that were previously part of the old kingdom Protista.Haplosporida: A phylum of EUKARYOTES in the RHIZARIA group. They are small endoparasites of marine invertebrates. Spores are structurally complex but without polar filaments or tubes.RNA, Ribosomal, 18S: Constituent of the 40S subunit of eukaryotic ribosomes. 18S rRNA is involved in the initiation of polypeptide synthesis in eukaryotes.Eukaryotic Cells: Cells of the higher organisms, containing a true nucleus bounded by a nuclear membrane.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.DNA, Ribosomal: DNA sequences encoding RIBOSOMAL RNA and the segments of DNA separating the individual ribosomal RNA genes, referred to as RIBOSOMAL SPACER DNA.