The phylum bryozoans, literally « moss animals », includes over 4,000 species.

The term bryozoan is currently synonymous with ectoprocts as it now only includes species from this phylum. Bryozoans are divided into 3 classes, one of which contains only fossil species, the stenolomes. Among the remaining two, the first, the phylactolomes, contains freshwater species, while the second, the gymnolomes - the larger group - is primarily marine.

As for the class of gymnolomes - the one that interests us the most as divers - it is divided into two orders: the ctenostomes and the cheilostomes.

Bryozoans are very small animals - on the order of a millimeter - characterized by a crown of tentacles with cilia surrounding their mouth. This crown of tentacles is called the lophophore and allows bryozoans to filter seawater in search of food.

In the case of marine species, the crown of tentacles is circular in shape, while it takes the form of a horseshoe for freshwater species.

The body of the animal is primarily made up of a U-shaped folded digestive tract: it begins with the mouth located at the center of the lophophore and ends with the anus, which is located outside the crown of tentacles. Bryozoans are primitive animals lacking respiratory and circulatory systems. The various exchanges occur through diffusion.

Some scientific terms to describe our little friends, the bryozoans ! Bryozoans are triploblastic and coelomate metazoans ! Let's go back a moment… Metazoans because bryozoans are multicellular animals and triploblastic, as they have three germ layers at the embryonic stage: the ectoderm, endoderm, and mesoderm. Finally, coelomate because bryozoans always have an internal cavity at the embryonic stage, which allows for the later development of the animal's vital organs.

Bryozoans live in colonies called zoaria. The colony is made up of a multitude of rigid cavities called zooecia, within which each individual, called a zooid, lives. The zooid itself consists of two parts: the cystid and the polypide or polyp.

Grouped together, bryozoans form colonies with very varied shapes, but characteristic of a given species. Sometimes encrusting, the colonies cover the entire substrate or sometimes they stand upright in the water in tubular form or as branched structures.

Bryozoans are widely distributed and can be found in all oceans and seas across the globe. The warm waters of tropical oceans and seas likely host the greatest variety of bryozoan species !

Under our latitudes in the Mediterranean sea, one of the most well-known bryozoans is certainly Neptune's lace !

Bryozoans live in colonies fixed to almost all types of substrates. This substrate can be mineral, such as rocks, sandy bottoms, wrecks or vegetal, like algae. It is also possible to find them fixed on sponges or even gorgonians.

Bryozoans particularly favor areas sheltered from light !

Bryozoans feed on particles and microorganisms suspended in the water through passive filtration of seawater.

Bryozoans exhibit:

• sexual reproduction, which results in the birth of a new zooid after fertilization and the development of the egg, followed by a larva
• asexual reproduction through the budding of a new zooid.

Bryozoans are preyed upon by many predators ! Among them are numerous mollusks, including nudibranchs, sea urchins and certain crustaceans.

Some species of bryozoans could prove to be very invasive, like the case of the bryozoan Trieellaria inopinata, which made its first appearance in Venice in 1982! Since then, this bryozoan has been reported at various locations along the Atlantic coasts of Europe. Several hypotheses have been proposed to explain the initial vector of this bryozoan's appearance: transported by pleasure boats, commercial ships, or live mollusks imported and introduced into the natural environment for commercial purposes… the mystery remains !

Be careful, some species of bryozoans can be mistaken for corals, such as false coral (Myriapora truncata).

Minuscule, the bryozoan is imperceptible ! Grouped into colonies, bryozoans appear in various shapes and forms, much to the delight of divers !