Bryozoans

Bryozoa is an exclusively aquatic phylum (both marine and freshwater) and is one of the most represented taxonomic groups in marine benthic assemblages,  especially on hard bottoms.
They are colonial sessile organisms and, although generally of very small dimension, they can form colonies of a considerable size, both erected and  encrusting.
Even though Bryozoans are widespread in all environments and depths, they are dominant particularly in some benthic communities of the continental shelf  that live on hard  and detritic bottoms (i.e. "praline " and "maerl" facies). Some of the bryozoan species play an important role as bioconstructors specially in the Coralligenous biocoenosis.
Many species are epiphytes on plants (algae and sea grasses), others are abundant in confined environments, like underwater caves, lagoons, coastal lakes and harbours. The Bryozoans are also the main component of marine fouling.
The Bryozoan fauna of the Mediterranean sea includes over 450 species, of which 341 have been found in the Italian Seas. The most represented taxon is the Cheilostomata order, with 262 species or subspecies reported. Individuals are named zooids. Each zoide has a body wall named cystid that includes the lophophore with tentacles and the internal organs, which together constitute the polypide. Individuals that are able to feed themselves are defined autozooids, whereas others zooids without tentacles and digestive tract variously reduced and modified, are defined eterozooids and perform other functions.