Species Names: Ciona intestinalis Oikopleura Branchiostoma (Amphioxus).

Urochordata – marine subphylum of chordates Sea squirts (eg. Ciona), pelagic forms (eg. Oikopleura) Cephalochordata – marine subphylum of chordates - lancelets

Explosion of invertebrate evolution in the lower Cambrian period (Beginning 570 million years ago) - lasted 10 million years. - Melting glaciers => more water/places to live Retinoic acid (a vitamin A-deirved morphogen) a possible component for their evolution. => too much or too little of it during embryo development could lead to mutations => evolutionary change Evolved from lancelets Notochord ( a cartilaginous rod along the back) No jaws

At some point in the invertebrate chordate life they have… A flexible, fibrous notochord that gives support. A hollow dorsal nerve cord in the back. Gill slits in the pharynx (throat area). Muscular tail which prolongs past the anus. (for locomotion and balance).

Urochordata Endoskeleton Cephalochordata Endoskeleton Endoskeleton- an internal skeleton made of bone or cartilage.

Urochordata are filter feeders. 1.) Water enters into the incurrent siphon 2.) It goes to the slits in the pharynx 3.) Food filtered by the pharynx moves to the stomach 4.) Undigested moves to anus 5.) And exits through excurrent siphon.

Cephalochordata are also filter feeders. 1.) Water is drawn by cilia into the mouth. 2.) It moves to the pharynx. 3.) The pharynx traps food particles from the water. 4.) Food enters the intestine for digestion 5.) The water leaves through atriopore. (An opening in the body).

Pike - Worlds first known chordate - large carnivorous, bony fish - genus Esox in the family Esocidae.

- Fish: the first vertebrates. - Example: Myllokunmingia, found from fossil deposits in China. -Earliest fish - lampreys and hagfishes -Ordovician period -jaws -=> major advancement -Earliest jawed fishes were covered in bony armor b/c of strengthening predatory race. => Placoderms => extinct - Jawed fishes that survived became: ChondrichthyesChondrichthyes (cartilaginous fishes) Osteichthyes (bony fishes). Osteichthyes

- About 99% of the animals in the world are invertebrates? -They are usually darker color on the top and lighter on the bottom to protect them from predators/enemies. - Their body shape is streamlined to allow it to move through water more rapidly. -They can change their color in an instant with color and reflective cells in their pigmentation! -Scales protect the fish and reduce the friction while they swim. -Fish are very diverse species… -Size range from 1 inch to 16 feet long!!! -They can be almost any color in nature

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