Bryozoans are tiny colonial aquatic animals that generally build stony skeletons of calcium carbonate. There are about 5000 living species known. They superficially resemble corals, and are sometimes called “moss animals”. Known to occur worldwide, they prefer warm tropical waters. Bryozoan phylum consists of three classes: 1) Stenolaemata, 2) Gymnolaemata, 3) Phylactolaemata which can be found in marine habitats and freshwater habitats, respectively. The marine species are distinguished by their soft-anatomy while the freshwater species are distinguished by the lack of zooid polymorphism, and calcification. There hasn’t been a mineralized fossil by this class, but there are some fossil records of tubes in deposits in the Tertiary age. Phylactolaemata, can overcome winter easily by forming overwintering structures (Statoblasts).
Stenolaemata have tubular zooids with calcified walls and their lophophore extends from body by annular muslcles and has five orders.
Gymnolaemata on the other hand have cylindrical or flattened zooids and their lophophore projects by muscles pulling on the frontal wall.
It should also be noted that Bryozoa phylogeny has been very limited, and is still being analyzed.
*~ Classification*~
+Class: Stenolaemata
O. Cyclostomata
O. Hederellida
O. Trepostomatida
O. Cystoporida
O. Cryptostomida
O. Fenestrida
+Class: Gymnolaemata
O. Ctenostomata
O. Cheilostomata
+Class: Phylactolaemata
O. Plumatellida
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