What are synapomorphies of chordates?

Synapomorphies are shared derived characteristics that define a particular group of organisms. In the case of chordates, the synapomorphies include:

1. Notochord: A flexible rod-like structure that runs along the length of the body, providing support and acting as a precursor to the vertebral column in vertebrates.

2. Dorsal hollow nerve cord: A hollow tube-like structure that runs along the dorsal side of the body, which develops into the central nervous system (brain and spinal cord) in vertebrates.

3. Pharyngeal slits or pouches: Series of openings in the pharynx region, which are used for filter-feeding, respiration, or as a precursor to gills in aquatic chordates.

4. Endostyle or thyroid gland: A glandular structure located in the floor of the pharynx, which secretes mucus or hormones, and is involved in filter-feeding or hormone regulation in different chordate groups.

5. Post-anal tail: An extension of the body beyond the anus, which is present in the embryonic stage and may be retained in some adult chordates, such as fish and humans.

These synapomorphies are present in all chordates, although they may be modified or lost in certain groups during development or evolution.