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Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike all other known metazoans, sponges' bodies consist of a non-living jelly-like mass (mesoglea) sandwiched between two main layers of cells.
Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as "basal lamina").
Demosponges use spongin, and in many species, silica spicules and in some species, calcium carbonate exoskeletons.
Demosponges constitute about 90% of all known sponge species, including all freshwater ones, and have the widest range of habitats.
Sponges were first to branch off the evolutionary tree from the common ancestor of all animals, making them the sister group of all other animals.
Sponge biodiversity and morphotypes at the lip of a wall site in 60 feet (20 m) of water.
All sponges have ostia, channels leading to the interior through the mesohyl, and in most sponges these are controlled by tube-like porocytes that form closable inlet valves.
Pinacocytes, plate-like cells, form a single-layered external skin over all other parts of the mesohyl that are not covered by choanocytes, and the pinacocytes also digest food particles that are too large to enter the ostia, Glass sponges present a distinctive variation on this basic plan.
Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells.
A few species of sponge that live in food-poor environments have become carnivores that prey mainly on small crustaceans.