What is the phylum chordata?

Chordate, a phylum of animals which includes all animals with backbones and several other types of animals: mammals, fish, amphibians, reptiles, birds; salps, sea squirts and lancelets.

Chordates form a phylum of creatures that are based on a bilateral body plan and is defined by having at some stage in their lives all of the following:

1. A notochord, in other words a fairly stiff rod of cartilage that extends along the inside of the body.
   Among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail.

   The final destination in mammals is the nucleus pulpous of the intervertebral disc.

   1. A dorsal neural tube. In fish and other vertebrates this develops into the spinal cord, the main communications trunk of the nervous system.

   2. Pharyngeal slits. The pharynx is the part of the throat immediately behind the mouth. In fish the slits, are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live.

   In mammals the most anterior pharyngeal arch gives rise to the oral jaw. The second arch becomes the hyoid and jaw support.
   And the anterior arches develop into components of the ear, tonsils, and thymus.

   1. Post-anal tail. A muscular tail that extends backwards behind the anus. In humans it forms the sacrum and coccyx.

   2. An endostyle. This is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus. It also stores iodine, and may be a precursor of the vertebrate thyroid gland.