Fish
The earliest evolution of fish has been dated back 500 million years to the Cambrian Explosion era. The earliest fish were like worms. Th earliest fish had the original features which are now crucial to this specifc class. Fish are bilaterally symmetrical, contain a nerve cord and a distinct head and tail. However, fish now contain V-shaped muscles which can be shown clearly on your dinner plate.
The evoltuion of fish has develop from a jawless, cartilaginous species to the oldest known living vertebrate species classed as Cephalaspidomorphi. Present day Lampereys are such a species, which are jawless and have the cartilaginous segmenst surrounding the notochord and partly over the nerve cord.
As mineralization developed, Conodonts became the first vertebrates that contained skeletal parts in the mouth and pharynx. With the development of bones and teeth through mineralization, a new class of fish with jaws evolved and is classified as the Gnathostomes. These skeletal supports derived from the paryngeal slits. With the development of a mineralized endoskeleton, the gnathostomes developed paired swim appendages to aid in maneuverability and defense. A sub-class of this species noted by the cartilaginous skeleton in sharks, and rays developed secondary to the ancestral mineralized skeleton.
These species which developed primarily a cartilage skeleton are considered Chondrichthyans. The second sub class deriving from the Gnathostomes is called the osteichthyes. These species consist of a bony endoskeleton and are esentially all the species we consider fish. Fish have the ability to breathe underwater through their gills which enable them to obtain oxygen which is dissolved into water. Tiny blood vessels absorb the oxygen as water enters the fishes mouth and runs over the gills, then the carbon dioxide is released with the water through the gills out of the fish.
Fish contain a two chambered heart. The atrium of a fish heart receives de-oxygenated blood and passes it onto the ventricle, the second chamber, which then pushes the blood over to the gills to be reoxygenated. The gas exchange occurs over the gills within the blood vessels and the oxygenated blood is pumped through the body until it returns back to the atrium. This cycle is then repeated over. Fish also have a swim bladder, an air sac, which helps control and aids them in their bouyancy underwater. Fish are an ectothermic species and therefore in order to regulate their body temperature they must continually try and find warmer water or colder depending on the temperature.
The evoltuion of fish has develop from a jawless, cartilaginous species to the oldest known living vertebrate species classed as Cephalaspidomorphi. Present day Lampereys are such a species, which are jawless and have the cartilaginous segmenst surrounding the notochord and partly over the nerve cord.
As mineralization developed, Conodonts became the first vertebrates that contained skeletal parts in the mouth and pharynx. With the development of bones and teeth through mineralization, a new class of fish with jaws evolved and is classified as the Gnathostomes. These skeletal supports derived from the paryngeal slits. With the development of a mineralized endoskeleton, the gnathostomes developed paired swim appendages to aid in maneuverability and defense. A sub-class of this species noted by the cartilaginous skeleton in sharks, and rays developed secondary to the ancestral mineralized skeleton.
These species which developed primarily a cartilage skeleton are considered Chondrichthyans. The second sub class deriving from the Gnathostomes is called the osteichthyes. These species consist of a bony endoskeleton and are esentially all the species we consider fish. Fish have the ability to breathe underwater through their gills which enable them to obtain oxygen which is dissolved into water. Tiny blood vessels absorb the oxygen as water enters the fishes mouth and runs over the gills, then the carbon dioxide is released with the water through the gills out of the fish.
Fish contain a two chambered heart. The atrium of a fish heart receives de-oxygenated blood and passes it onto the ventricle, the second chamber, which then pushes the blood over to the gills to be reoxygenated. The gas exchange occurs over the gills within the blood vessels and the oxygenated blood is pumped through the body until it returns back to the atrium. This cycle is then repeated over. Fish also have a swim bladder, an air sac, which helps control and aids them in their bouyancy underwater. Fish are an ectothermic species and therefore in order to regulate their body temperature they must continually try and find warmer water or colder depending on the temperature.
Reference:
Vertebrate Zoology, "Perch Dissection", Retrieved from website April 13, 2013, http://www.savalli.us/BIO370/Anatomy/3.PerchDissectionLabel.html
Picture retrieved form Website April 13, 2013, http://0.tqn.com/d/cookingfortwo/1/0/_/E/-/-/jerk-mahi-mahi12-500.JPG
Picture retrieved form Website April 13, 2013, http://0.tqn.com/d/cookingfortwo/1/0/_/E/-/-/jerk-mahi-mahi12-500.JPG