Eumetazoa in the context of "Epidermis (zoology)"

Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (/pəˈrɪfərəˌ pɔː-/; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and are one of the most ancient members of macrobenthos, with many historical species being important reef-building organisms.

Sponges are multicellular organisms consisting of jelly-like mesohyl sandwiched between two thin layers of cells, and usually have tube-like bodies full of pores and channels that allow water to circulate through them. They have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. They do not have complex nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, usually via flagella movements of the so-called "collar cells".

Parazoa (Parazoa, gr. Παρα-, para, "next to", and ζωα, zoa, "animals") is an obsolete subkingdom that is located at the base of the phylogenetic tree of the animal kingdom in opposition to the subkingdom Eumetazoa; they group together the most primitive forms, characterized by not having proper tissues or where, in any case, these tissues are only partially differentiated. It generally includes a single phylum, Porifera, which lack muscles, nerves and internal organs, which in many cases resembles a cell colony rather than a multicellular organism itself. All other animals are eumetazoans and agnotozoans (Agnotozoans are possibly paraphyletic or even nonexistent in studies), which do have differentiated tissues.

Agnotozoa is a subkingdom of simple animals that is sometimes used. It is one of the three "traditional" animal subkingdoms, along with Parazoa and Eumetazoa. On some classifications, it is nearly synonymous with Mesozoa.

Agnotozoa was first used as one of the branches of the subkingdom Metazoa. It was then considered to contain only one group, Mesozoa.

A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce two or three primary germ layers. Some animals, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic. Other animals such as bilaterians produce a third layer (the mesoderm) between these two layers, making them triploblastic. Germ layers eventually give rise to all of an animal's tissues and organs through the process of organogenesis.