The diversity of species in the marine environment surpasses terrestrial environments. Virtually every phyla of animals is represented in the ocean and some phyla are limited to the ocean.
Phyla are major divisions of plants and animals.
Organisms are considered more closely related, in evolutionary terms, to members of their own phylum than to members of other phyla. Similarly, within a phylum, organisms are divided hierarchically in categories according to degrees of relatedness. Not all phyla are discussed and not all classes within phyla are discussed. Pictures of species are included where available. Sponges are aggregations of cells that do not form tissues or layers but are organized around a system of pores, canals and chambers.