Briozoi - Bryozoa
Bryozoa phylum (Briozoi) or more correctly Ectoprocta is made up of small aquatic invertebrates, almost exclusively marine, living in arborescending columbians anchored to a submerged substratum.
Etymology From the Greek brion = moss and zion = animal, since the appearance of the colonies remembers that of the moss.
Distribution and Habitat The Briozoi live on rocky, but also sandy and lush vegetation, prefer tropical marine environments, but for their worldwide distribution they can be called cosmopolitans.
Description A Briozoi colony is made up of individuals, called zooids, which reach a maximum of half a millimeter. Each living zoo is enclosed in an elongated casing, a double wall, limestone or chitosan, said zooecio, sometimes closed by an operculum.
Each individual consists of a part permanently inside the teacup, called the cystite, and one that comes out, called the polypipe. The latter is equipped with a ridge detected, the loophore, which carries a crown of tentacles around the mouth opening, which act as organs for nutrition, breathing and perception of external stimuli. The cystide constitutes the fundamental part of the animal as it is itself securing the zooecio and regenerating the polypide if necessary.
The loophore in the marine Briozoi has circular shape, while in the freshwater it is a form of horsehair.
The polypide can be quickly portrayed in a zoo through a muscle retractor and can then be extracted with parietal muscles. Eversion takes place much more slowly, according to two different mechanisms:
If the zoo is not so calcified and therefore elastic, the parietal muscles connected to the cystide contract, deforming the body of the animal and increasing the pressure of the internal fluid, which causes the polypide to collapse into the hole. If, however, the zoo is very calcified and therefore rigid, it can not be deformed and therefore another mechanism is exploited: an inner bag full of water and communicating with the outside (asco) is expanded by contraction of muscles connected to it. That its volume expansion causes the increase in pressure of internal liquids and the collapse of the polypids. The Briozoids do not have a circulatory system. They have a curved U-shaped digestive system, with mouth close to the anus at the top and stomach and intestine in the lower one.
Some species have, like nervous system, a nervous ganglion under the loophore.
Colonies are generally polymorphic, ie zooids may assume a different morphology depending on their function. The characteristics are the aviculari and the vibraculari. The avoculars have a shape that remembers the head of a bird (hence the name), with the modified operetto to form a beak with defensive function. The vibrations, however, have a considerably elongated and muscled operation that pass on the colony to clean it off the debris.
Biology These animals reproduce both sexually and sexually. The founder of the new colony, called ancestrula, originates from the other zooids, which consequently have all the same genetic heritage. Within the same colony, however, there is a large morphological differentiation between different individuals according to their role (cleaning, reproduction, defense, etc.).
Briozoons are generally hermaphrodites. Most marine species belonging to this phylum retain the embryo in an incubator chamber attached to the zoo, feeding it through a placental tissue. From the embryo develops a trocar-like ciliary lizard called the typhoon, which has the appearance of a flattened cone with apex limb. The larvae, after hatching, descend to the seabed and, with the tip pointing downward, fasten on a substrate by founding a new colony for cramping.
In addition, it should be noted that Bryozoa also includes the Entoprocta subtype, with mouth and anus opening inside the loophore. Of these forms there is no fossil testimony, since they are without skeleton.
Supply The Briozoi bake of plankton and organic particles that capture by filtering the water.