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Introduction: You are a member of the phylum Chordata. If you think about to which organisms you are related, even distantly, it is certain you can come up with some general common characteristics you all share. However, those traits that are distinguishing among the chordates are not necessarily visible in all members of the phylum. However, they all do express these traits at some point within their lives.

All chordates have the following traits:
1. notochord - this will become the spinal cord in many vertebrates.
2. dorsal hollow nerve cord - this becomes the nervous system.
3. pharyngeal slits - in some organisms these remain as gills, while in others they become part of the jaw structure.
4. post-anal tail - many organism retail the tail, but in some organisms it is greatly reduced.

The lancelet (below) is an organism that retains all four of these traits throughout its entire life

The chordates can be further broken down into non-vertebrate chordates and vertebrate chordates. Yes, there are some members of this phylum that display all four required traits, but are considered invertebrates. These include a group of marine filter-feeders called sea squirts.

The vertebrate chordates can be classified into five main groups. These are most likely the animals about one thinks when the subject comes up. The main groups of vertebrates are the amphibians (class Amphibia), fish (class Pisces), reptiles (class Reptilia), birds (class Aves), and mammals (class Mammalia).

Directions for this Lesson: Answer the practice questions and then watch the video to learn more about the characteristics of chordates.

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