which Animl have peculiar sermatozoa
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Moss animal, also called bryozoan, any member of the phylum Bryozoa (also called Polyzoa or Ectoprocta), in which there are about 5,000 extant species. Another 15,000 species are known only from fossils. As with brachiopods and phoronids, bryozoans possess a peculiar ring of ciliated tentacles, called a lophophore, for collecting food particles suspended in the water. The bryozoans are a widely distributed, aquatic, invertebrate group of animals whose members form colonies composed of numerous connected units called zooids (hence the term Polyzoa, which means “many animals”). Individual zooids are usually no more than one millimetre (0.04 inch) long, although colonies of some species can exceed 0.5 metre (about 20 inches) in diameter. Until the mid-18th century, bryozoans, like corals, were regarded as plants; hence the name, which means “moss animals.” Seventy-five years later, the bryozoans were distinguished from the cnidarians, and the characteristic structure of the zooid was first described.
Bryozoans are separated into three classes: Phylactolaemata (freshwater dwelling); Stenolaemata (marine); and Gymnolaemata (mostly marine). The order Cheilostomata (class Gymnolaemata), containing 600 genera, is the most successful bryozoan group.
General Features
Distribution and abundance
Bryozoan colonies are found in both fresh and salt waters, most commonly as growths or crusts on other objects. Freshwater bryozoans live among vegetation in clear, quiet, or slowly flowing water. Marine species range from the shore to the ocean depths but are most plentiful in the shallow waters of the continental shelf. They cover seaweeds, form crusts on stones and shells, hang from boulders, or rise from the seabed. Bryozoans readily colonize submerged surfaces, including the hulls of ships and the insides of water pipes. A few types of bryozoans form nonattached populations on sandy seabeds.
The zooid walls, which constitute the most permanent portion of the colony, generally are calcareous (i.e., impregnated with calcium carbonate), giving bryozoans a fossil record that dates from the Ordovician onward (i.e., from about 500 million years ago).
Size range and diversity of structure
Although the component zooids rarely exceed one millimetre in length, bryozoan colonies—formed of numerous asexually budded zooids—vary greatly in size. In the gymnolaemate genus Monobryozoon, which lives between marine sand particles, a colony consists of little more than a single feeding zooid less than one millimetre in height. Colonies of the European Pentapora, however, can reach one metre (3.3 feet) or more in circumference; a warm-water gymnolaemate genus, Zoobotryon, which hangs from harbour pilings, and the freshwater phylactolaemate Pectinatella each produce masses that may be one-half metre across. Colonies that form crusts generally cover only a few square centimetres; erect colonies may rise only two to five centimetres (0.8–2 inches).