It is also used for axial support in lower chordates. These form in the early embryo and develop into gill slits in fish and primitive chordate, and as vocal chords in higher chordates. Clearly evident in animals such as dogs and cats. In deuterostomes, the anus forms from the embryonic blastopore. Echinoderm endoskeleton is a network of spicules.
Chordate endoskeletons are bones.
The exoskeleton servers as protection as well as provides attachment sites for muscles used in locomotion. However, arthropoda truly shows the most significant advancement of appendages. This is seen to a small degree in nematode, but to a much larger degree in annelids, arthropods and chordates. This terms describes the way that animals bodies are organized into repeating units called segments. Annelids are the first animals to show this type of organization.