The X–ray tetra (Pristella maxillaris) is one of the few chordates with a visible backbone.
The spinal cord is housed within its backbone.
Classification of animals: There are 10 major phyla in the animal kingdom. The most important features of these major animal phyla, their classification and examples are as follows:
- Porifera : Includes the sponges.
- Coelenterata: Includes Cnidaria.
- Ctenophora: Ctenophores, commonly known as sea walnuts or comb jellies are exclusively marine.
- Platyhelminthes: Flatforms and acoelomates.
- Aschelminthes: These are also known as Pseudocoelomates/ nematods.
- Annelida : These are also said to be Protostome Coelomates. Animals in the phylum Annelida include the earthworms, leeches, and many marine worms.
- Arthropoda: Arthropods are segmented. Largest group among animal kingdom, includes cockroaches, spiders...etc.
- Mollusca: These are also said to be Protostome Coelomates. Animals in the phylum Mollusca include clams, snails, octopuses, and sea slugs.
- Echinodermata: Representatives of the phylum Echinodermata are common inhabitants of coastal tide pools (or even our local saltwater aquarium ). Sea lilies, sea stars (starfish), and most other echinoderms are sessile or slow–moving animals.
- Chordata : Chordates embody many sophisticated evolutionary adaptations. They have four major characters that distinguish them from other deuterostomes: a notochord, a dorsal nerve cord, pharyngeal slits, and a postanal tail.
Vertebrates are animals that are members of the subphylum Vertebrata (chordates with backbones and spinal columns).
Subphylum Vertebrata: Subphylum Vertebrata includes organisms with several basic features, in addition to the typical chordate characteristics. Vertebrates exhibit the most pronounced cephalization, in which the anterior portion of the nervous system (the brain) is enclosed inside a protective case (the skull). These animals all have a vertebral column (backbone) that serves to support the head, anchor muscles, and protect internal organs. The dorsal nerve cord is protected by the vertebral column, and the anterior portion of this nerve cord is protected by a cranium. Humans belongs to subphylum Vertebrata and Phylum Chordata.