Hydras are a genus of the Cnidaria phylum. Borrelia is a genus of bacteria of the spirochete phylum. Mammalia is a class of animal within the phylum Chordata. A chordate () is an animal of the phylum Chordata. Enterococcus is a large genus of lactic acid bacteria of the phylum Firmicutes. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. Hemichordates form a sister phylum to the echinoderms. Molluscs have more varied forms than any other animal phylum. The idea of body plans originated with vertebrates, which were grouped into one phylum. It is uncertain whether the phylum is monophyletic. Among the phytoplankton are members from a phylum of bacteria called cyanobacteria. This is characteristic of the phylum now called the "Cnidaria". Chlamydia is a phylum of intracellular parasites. They have been regarded as a paraphyletic phylum, from which the higher animals have evolved. An earthworm is a tubular, segmented worm of the phylum Annelida.