Chordates (Chordata)

Phylum of animals

Food, Animal source foods

Consumption area(s): Earth

Introduction

Chordates (Chordata) are bilaterally symmetrical animals that belong to the phylum Chordata. They are set apart from other animal groups by the presence, at some stage of their development, of a suite of distinctive anatomical features. These include a notochord, which provides internal support, a hollow dorsal nerve cord running along the back, and an endostyle (or thyroid gland) involved in feeding and metabolism. They also have pharyngeal slits, which assist in respiration or filter-feeding, and a post-anal tail that extends beyond the digestive tract.

Descirption of chordates (Chordata)

Chordates constitute a phylum of animals distinguished by the presence, at some point in their life cycle, of a set of specific anatomical traits.

One of these features is the notochord, a flexible yet sturdy rod made of glycoproteins wrapped in collagen helices that runs along the central axis of the body. In vertebrates, this structure is largely replaced by hyaline cartilage or bone forming the vertebral column, while remnants of the notochord contribute to the intervertebral discs, allowing adjacent vertebrae to bend and rotate. In fully aquatic species, the notochord aids in swimming efficiency, enabling lateral tail movements.

Chordates also possess a neural tube, which develops into the spinal cord, the main communication pathway of the nervous system. In vertebrates, the anterior portion of the dorsal nerve cord expands into vesicles during embryonic development, giving rise to the brain.

The pharyngeal slits, located in the throat immediately behind the mouth, serve different roles depending on the species. In fish, they are modified into gills, whereas in some other chordates they function in filter-feeding, capturing food particles from water.

A post-anal tail, a muscular extension beyond the anus, is present in all chordates at some stage. In certain species, it exists only during embryonic development.

The endostyle, a groove along the ventral wall of the pharynx, secretes mucus to trap food particles and guide them to the esophagus in filter-feeding species. It also stores iodine and is considered a precursor to the thyroid gland in vertebrates.

Beyond these defining features, all chordates share additional characteristics. They are deuterostomes, meaning the anus forms before the mouth during embryonic development. Their body plan is bilaterally symmetrical, and they have a coelom, possessing a fluid-filled body cavity lined with a membrane derived from the mesoderm.

Classification of chordates (Chordata)

Chordates are classified into 3 subphyla:

• Cephalochordates (lancelets)
• Urochordates (salps, sea squirts)
• Vertebrates (amphibians, birds, fish, mammals, reptiles)