Describe in depth what makes a chordate? Does this mean that all vertebrates are chordates and why/why not?

A chordate is an animal belonging to the phylum Chordata, which includes animals with certain common features at some point during their development. These features are:

1. A notochord: This is a flexible, rod-shaped structure that is found in the embryonic stage of all chordates. It extends the length of the body, providing support, and in some species, it persists throughout life.

2. A dorsal hollow nerve cord: This is a tube-like structure located above the notochord, which develops into the central nervous system: the brain and spinal cord.

3. Pharyngeal slits: These are openings in the pharynx, the part of the body that connects the mouth to the digestive and respiratory systems. In fish and some amphibians, these develop into gills. In terrestrial vertebrates, they develop into parts of the ear and tonsils.

4. Post-anal tail: This is an extension of the body that runs past the anal opening. In many species, it reduces during embryonic development into a structure within the body, but in some, it extends beyond the anus.

Now, to answer your second question, all vertebrates are indeed chordates. This is because vertebrates, which include animals like mammals, birds, reptiles, amphibians, and fish, all share the four key characteristics of chordates at some point in their development. However, not all chordates are vertebrates. This is because the phylum Chordata also includes two invertebrate subphyla: Urochordata (tunicates) and Cephalochordata (lancelets), which do not develop a segmented vertebral column, a key characteristic of vertebrates.