The phylum Chordata includes thousands of species found worldwide, but this guide will only cover a few classes. First, all chordates share the following four primary characteristics.
Since these phylum characteristics cover a wide variety of organisms, it is interesting to note that although two species may look very different, they can still be related. For instance, sea squirts first develop with a dorsal hollow nerve cord, meaning they are more related to humans than a sea slug!
As you read through the chordates in this section you will notice that they are grouped by classes, all of which are found in the subphylum Vertebrata. The following five classes are explored in the guide.