Bryozoan Fossils

Actinolite Picture

The Bryozoan, commonly known as moss animal, is a member of the Bryozoa phylum, which possesses more than 5000 species in the group. These species are aquatic and invertebrate, which is usually found in the tropical water and sometimes in the oceanic trenches. One of the most abundantly found fossils is the Bryozoan fossil. The first appearance of Bryozoan in the fossil records was approximately 450 million years ago during the Ordovician era. The other synonyms are Polyzoa and Ectoprocta.

Fossils were first found in the Ordovician period near the rocky areas and the oldest Bryozoan, which possessed a soft body compared to the others in this phylum, was found at the beginning of that period, Around 251 million years ago, during the Paleozoic era, marine fossils possessed an erect posture.

The Bryozoan reproduction process is carried out in both ways, sexually and asexually. In the asexual reproduction, the process called budding helps to produce the Zooid (progeny) which remains intact and connected, and develops a colony. Gradually the budding process causes the colony to enlarge, which in turn helps the Zooid to mature sexually to produce the spermatozoa and eggs.  In sexual reproduction, the gametes are produced and the fertilized eggs turn into swimming larvae. The Bryozoans are usually hermaphroditic, which means each living organism consists of both the ovary and the testes. Some species discharge eggs and sperms at the same time into the water where they fertilize. But sometimes, eggs are also fertilized inside the Ovicells, a special chamber, by capturing the sperms swimming freely in the water with the help of the tentacles, to fuse the eggs. After the fertilization, the eggs escape the chamber and then turn into a free swimming larvae.

The Bryozoan is aquatic animal and most of them are marine organisms except the newly discovered species known as Phylactolaemata which is often found in the fresh waters. The Bryozoan is always attached to hard surfaces like wood, rock, sand, shells, kelp blades and grains. Sometimes other organism like algae are also found covered abundantly with the Bryozoan. There are certain Bryozoan that do not grow on any hard substrates, but prefer to settle down on the sediment by forming colonies. It prefers any locations, and can be seen in polar waters, deep trenches as well as shallow waters. It has a record of living at 8200 meters depth. Most types of Bryozoans are immobile whereas some in the colony form are  seen to be creeping around the sand grains.

The Bryozoans feed on the tiny Planktonic particles flowing in the water. They are referred as filter feeders for sieving food particles with the help of Lophophore tentacles. The water is drawn towards the funnel top by the beating of the long cilia and the water is thus pushed out of the tentacles. This helps the food particle, present in the water to reach near the mouth. The process of digestion and food absorption is carried out in the stomach, whereas the undigested food is expelled through the body as a fecal pellet.

Respiration and Circulation
The Bryozoan organism does not have heart, respiratory organs or blood veins and vessels, but instead, by the process of diffusion, the Zooids carry out the process of oxygen intake and exhalation of  the carbon dioxide. The diffusion process is carried out by using a fine membrane or by the use of Psuedopores situated on the outer part of the Zooids. For the circulation of nutrients and oxygen, different methods are adopted by different species of Bryozoans. In some Bryozoans, the circulation is carried out with the help of large gaps situated in the body walls that allow the coelomic fluid to carry the nutrients, freely and in the others, the Funiculi or the internal threads are connected with the help of small pores present in the wall of the body to exchange the nutrients.

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