Classifying Animals into Phyla Study Guide (page 2)

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Updated on Sep 22, 2011

Classifying Animals into Phyla

Phylum Porifera: sponges

    Collections of individual cells, with no tissues or organs, and no nervous system or skeleton.

Phylum Coelenterata: jellyfish, sea anemones, coral

    Usually very beautiful forms, their bodies are two-layered and symmetrical in a circular fashion with rudimentary organs and systems, but no skeleton.

Phylum Platyhelminthes: flatworms, tapeworms

    Their bodies are symmetrical in a left/right fashion (like humans). Their bodies have three layers and have very rudimentary nervous tissue.

Phylum Nematoda: roundworms

    They are symmetrical like the flatworms and have three body layers. Many are beneficial soil organisms, whereas some are parasites (such as hookworms and pinworms).

Phylum Annelida: segmented worms

    These have bodies similar to other previous worms but with some more advanced characteristics, including sensory organs and a relatively developed nervous system. Their bodies are divided into segments; earthworms are the best example of animals in this category.

Phylum Echinodermata: sea stars and sea urchins

    Their bodies have a circular symmetry with five body parts being arranged around a central axis. They have calcium spines or plates just under the skin and a unique water vascular system that is a series of fluid-filled vessels that provide body support and allow for locomotion.

Phylum Mollusca: snails, clams, and octopuses

    These have a well-developed circulatory system, nervous system, and digestive system; octopuses have particularly well-developed brains with highly maneuverable tentacles.

Phylum Arthropoda: crustaceans, spiders, and insects

    This phylum has more species than the other phylums, mostly because of all the insect species. Their bodies have exoskeletons, and most undergo metamorphosis (a transformation that allows them to grow by shedding their exoskeleton and developing into a larger or more adult form). They often have specialized body parts (antennae, pinchers, etc.), and they are well adapted to many environments.

Phylum Chordata: amphibians, reptiles, fish, birds, and mammals (including humans)

    These are the most familiar animals, and we all share four characteristics: a notochord that often develops into the vertebral column in vertebrates; a nerve cord that runs along our backs; gill slits at some point in our development; and a tail or at least a vestigial tail (humans have the tailbone or coccyx).

In Short

As multicellular animals, animals must come up with solutions to several basic problems. These solutions give animals a different appearance from plants. These problems fall into several broad categories: surface-area-to-volume issues, body support and protection, locomotion, and sensory integration. Animals are also organized into several phyla.

Practice problems of this concept can be found at: Classifying Animals into Phyla Practice Questions

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