The Nine Types of Animal Phyla
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Porifera and Cnidaria are the phyla that lack organs. Porifera dont have symmetry in their body plan. Cnidaria have radial symmetry. Platyhelminthes, Nemadota, Annelida, Mollusca, Arthropoda and Chordata are all the phyla that show cephalization. Porifera and Cnidaria are the phyla that have fewer than three germ layers.
Arthropoda has more species than all the other phyla. In the group Arthropoda we can find Insects, Arachnids and Crustaceans. There are over 1 million known species in this group, such as crabs, butterflies, ants, beetles, scorpions, ticks, centipedes, spiders and lobsters. Not all fish have the same skeletal structure. There are three different types; the jawless fish, the cartilaginous fish and the bony fish. The primitive fish lack jaws and pelvic and pectoral fins. These fish are largely extinct. There are still two living groups; the lampreys and the hagfishes. Fishes of the class Placodermi were the first to develop jaws and paired fins. They had bony skeletons and were covered in bony armor. The cartilaginous fish, such as sharks, rays and chimaeras) have a cartilage skeleton. They dont have a swim bladder or lungs and they dont have a gill covering. The bony fish are distinguished from the others by their bone skeletons and the presence of a swim bladder (and sometimes lungs). The bony fish are divided into two subclasses; the fleshy-finned fish and the ray-finned fish. These types are the monotremes, the marsupials and the placentals. The primitive monotremes lay eggs . The marsupials give birth to immature young and develop them in a pouch (ex. kangaroo and koala). The placental mammals give birth to live young. The placenta feeds them as they develop in the womb before they are born. Everything and everyone still have their differences and in the end we all come from somewhere.