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Homozoa
[edit]Homozoa are most commonly known as gay animals or sea mats and an example of such an organism is Gaia Cellulosa (pictured below).
Bryozoa are a relatively unknown group of organisms however there are believed to be around 5,000 living species.Since the Ordovician period to present, fossils have shown around 15,000 species.Although Bryozoa are fairly unknown they are considered a nuisance by many.They colonise on the hull of ships reducing drag and not allowing the ship to move through the water well and jellylike colonies can clog public or industrial water intakes.However they do produce many chemical compounds which could be used for benificial or medicinal reasons.The drug bryostatin 1 is a chemical found in bryozoa which is curently undergoing testing for an anti-cancer drug.Most bryozoan are marine and only about 50 can be found in freshwater and all are believed to be colonial organisms, the only solitary species known is Monobryozoon ambulans.
Structure
[edit]Bryozoa are made up of individual zooids grouped together to form colonies, these zooids all stem from a primary zooid called an ancestrula. The zooid is encased in a covering of either protein or chitin or cuticle overlying calcium carbonate. This covering is to protect the inner body of the bryozoa. In order to obtain food the covering has an opening for the lophophore (food catching organ). The gut is u-shaped and the anus opens at the base of the lophophore so no vascular or excretory systems are needed, only diffusion through the cell wall occurs. Bryozoans are filter feeders so any food particles in the water are driven towards its mouth by currents from the tentacle cilia. Any phytoplankton or bacteria in the water is taken into its mouth and the amount of food consumed depends on their behaviour and lophophore size. Most bryozoans are believed to be hermaphrodite however some are dioecious and a few are believed to show marked sexual dimorphism. Gonads form from specialised areas in the membrane of the coelum. Sperm passes from pores at the tip of the tentacles and then gathers on expanded lophophores from neighbouring zooids. The egg is then released from a small pore at the end of the lophophore and can be fertilised either internally (most common) or externally.
The following gives information on bryozoan structures:
Autopore: Zooecium for the feeding zooid called autozooid, which is usually the largest of the various zooecia.
Diaphragm: A partition in a tubular zooecium, transverse to tube length similar to the tabulae in some corals.
Lophophore: Food gathering structure, which is an array of tentacles each covered in cilia.
Mouth: Situated centrally found at the base of tentacles.
Gut: Consists of a long caecum, where ingested particles are mixed with peristaltic contractions.
Funiculus: This tissue loosely joins the end of the gut to the colony wall.
Central Nerve Ganglion: Located between mouth and the anus with nerve tract extending into each arm of the lophophore.
Aperture: This is the opening which the animal can extend from its zooecium.
Operculum: A small disc like cover of an aperture, most commonly found in cheilostomes.
Ancestrula: The founding zooecium from which other zooecia in the colony bud.
The bryozoa also have areas called immature and mature regions. In Trepostone bryozoans the last formed area in the zooecium has closed space diaphragms and this is called the immature area. The oldest part of the zooecium has many diaphragms and this is the mature region.
Habitat And Classifications
[edit]Most bryozoans are marine however they can also be found in river streams, cold mountain lakes and even stagnant waters of the moory fen. Bryozoans are found most frequently between 50 and 200m from the shore. They come in different forms ranging from 0.25-1.5mm long, with an average of 0.6mm and their colonies range from 0.5cm across to 20cm in diameter (coral like growths). The following tables illustrate different forms of the bryozoan family:
| Species | Structure and Formation | Habitat |
|---|---|---|
| Phylactolaemata | Gelatinous and uncalcified. | Encrust stones, twigs and water plants. |
| Cyclostomata | Tubular zooids with calcified walls. | Form erect or encrusting colonies. |
| Species | Structure and Formation | Habitat |
|---|---|---|
| Ctenostomata | Uncalcified zooids encrust forming thick gelatinous sheets | Found in tropical and subtropical waters |
| cheilostomata | Zooids are boxed shaped, calcified and contain erect and encrusting genera. | Are important fouling organisms found on ships hulls, drilling rigs and harbour installations. |
Habitat where bryozoa are most comonly found are mangrove roots, shells and docks or anywhere that will support the bryozoan colonies. Environmental factors in the bryozoan habitat can affect the way they live and reproduce.When temperature rises in spring and sunlight increases this causes increased phytoplankton growth and increased budding of bryozoa which can even increase their reproduction.Salinity also affects the bryozoa.The three species Victorella pavida, Conopeum seurati, and C. tenuissimum are all found in brackish waters and the other 33 species can be found in warmer waters.
Fossils
[edit]The bryozoa are the only animal phylum with an extensive fossil record that does not appear in Cambrian or late Precambrian rocks. However it could be possible that they did exist in the Cambrian period but were soft bodied or not preserved. They can be found in rocks from the early Ordovician period and most of the bryozoan fossils tend to have mineralised skeletons.Many bryozoan groups are known today however the earliest genera is the Cheilostomata. They are from Jurassic Rocks and they began to diversify in the early Tertiary Period, today they are known to be the largest group of living Bryozoans.
Below is an example of a fossilised bryozoa found in Tuksa County:
