![]() Class Scyphozoa allows for the medusa stage to be dominant. Class Scyphozoa is the final class within phylum Cnidaria. Coral, sea pens, and sea anemones are some examples of this class. Class Anthozoa allows for the organisms to be a polyp for its entire life. For instance, class Hydrozoa allows for the organism to be polyp for most of its lifetime. There are three different classes within this phylum that contains different life cycles and different stages of polyps and medusas. One of the main components to this phylum is that the undergo something called "Alteration of Generation." This is when the organism is a polyp for a bit of its life and then it alternates into becoming a medusa. This phylum now contains 2 true tissue layers, making them diploblastic and they also have radial symmetry. Cnidarian literally translates to "nettle", implying that they sting and that they include a nervous system. Cnidarians are the second most primitive, multicellular organisms known. Phylum Cnidaria is one step above the Porifera's, when it comes to advancements. Organisms in the Porifera phylum are found on ocean floors or in fresh bodies of water. A sperm is released from the sponge and travels to another sponge where and archaeocyte greets it and guides it to the egg. Sexual reproduction is done by internal fertilization. Once the conditions are favourable, the gemmules will grow into an adult sponge. Gemmules are only produced when there is harsh environmental conditions. Budding is when a sponge breaks a bit of itself off, then the broken bit settles to the sea floor and grows into an adult sponge. Asexually, the sponge produces a budding or producing gemmules. ![]() Reproduction is done either sexually or asexually. ![]() All functions are carried out by the specialized cells and for protection, toxins are released whenever a sponge feels in danger. Since Porifera's are so primitive, this means that they don't have and organs that are used for a nervous system. The movement of water helps circulate water through the body without the use of special tissues or organs. Circulation also relies on water to carry out it's body function. Oxygen is dissolved into the water and then it diffuses into the surrounding cells (collar cells) in the "sac" of the sponge. Respiration takes place as water moves through the body. They are diffused out of the sponge through water. Excretion also uses water to preform its function as CO2 and other wastes are diffused into the water and carried out of the sponge through the osculum. Archaeocytes then receive the nutrients from the collar cell and they complete the process by spreading and transport these nutrients through the sponge. Collar cells line the inside of the cell. This takes place inside the sponge as the collar cells trap and engulf the microscopic particles that float in along with the water. Sponges are "filter feeders", meaning that they sift food from the water that enters the sponge through the incurrent pores. Nutrition, respiration, circulation and excretion are require water in order to perform their duties to the sponge. Water is a HUGE component to this phylums survival. This leads to poorly developed organs and the body plan becoming a "sac-plan." Choanocytes, osculum, spicules and archaeocytes are just a few of the specialized cells that allow the sponge to survive. Sponges are acoelomates meaning that they do not have a coelom or a body cavity. With no tissue layers, this phylum only uses specialized cells such as spicules and spongins to make up the organism's structure. The word Porifera means "pore-bearing" making most of the organisms in this phylum to be sponges. Phylum Porifera contains the most primitive organisms that are known.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |