FISH

FISHES

• a limbless cold-blooded vertebrate animal with gills and fins and living wholly in water. "the sea is thick with fish"

Chordata: Subphylum Vertebrata

• Vertebrates constitute the vast majority of living chordates, and they have evolved an enormous variety of forms.

• possess a backbone (aka vertebral column spine)
• vertebrae=Dorsal row of hollow skeletal elements(usually bone)
• nerve cord=spinal chord,protected by vertebrae.(part of nervous system)ends in brain
• bilateral symmetry,endoskeleton

AGNATHANS(AGNATHA)

• It is came from the Greek word[4] ἀ-γνάθος "no jaws") is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species.

• Agnathan, (superclass Agnatha), any member of the group of primitive jawless fishes that includes the lampreys (order Petromyzoniformes), hagfishes (order Myxiniformes), and several extinct groups. 

Kingdom:Animalia

Phylum:Chordata

Subphylum:Vertebrata

Superclass:Cyclostomata

Class:Myxini

Order:Myxiniformes

Family:Myxinidae

HAGFISH :(order Myxiniformes)

• Hagfish, of the class Myxini (also known as Hyperotreti), are eel-shaped, slime-producing marine fish (occasionally called slime eels). They are the only known living animals that have a skull but no vertebral column, although hagfish do have rudimentary vertebrae.
• Hagfish are widely considered the most disgusting animals in the ocean, if not on earth. The eel-shaped creatures use four pairs of thin sensory tentacles surrounding their mouths to find food—including carcasses of much larger animals.
• The estimated 76 species of hagfishes live in cold waters around the world, from shallow to as deep as 5,500 feet (nearly 1,700 meters).
• Hagfish can absorb nutrients straight through their skin.
• They are sometimes called “slime eels”—but they are not eels. They are in the class Agnatha, designated for fish without jaws (around 100 species in total).

CLASS CEPHALASPIDOMORPHI

• Cephalaspidomorphs are a group of jawless fishes named for Cephalaspis of the osteostracans. Most biologists regard this taxon as extinct, but the name is sometimes used in the classification of lampreys, because lampreys were once thought to be related to cephalaspids. 

Scientific name: Cephalaspidomorphi

Extinction status: Extinct Encyclopedia of Life

Rank: Class

Higher classification: Craniate

Phylum: Chordata

LAMPREY: (order Petromyzoniformes)

• Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes, placed in the superclass Cyclostomata.
• The sea lamprey is a fish that is eel-like in appearance. 
• It has a skeleton made of cartilage and lacks a jaw.
• This species has seven gill openings, two fins along its backs, and no side fins. 
• The sea lamprey has a large, round mouth with sharp, curved teeth
• Ocean-dwelling sea lamprey can grow up to 47 inches (120 cm) in length. Freshwater sea lamprey can grow up to 25 inches (64 cm) in length.

GNATHOSTHOMES

• Jawed vertebrates with teeth develop from modication of skeletal rods between pharyngeal gill slits.
• other features of gnathothomes:

1. additional duplication of hox genes
2. enlarged forebrains-enhanced sense of vision and smell.

*Leteral line system-rows of microscopic organs sensitive to vibrations in the water.

Example:sharks,rays,ray finned and lobe finned fish.

 *SHARK:

*RAYS FISH

*RAY FINNED FISH

*LOBE FINNED FISH

TWO EARLY GROUPS OF GNATHOSTHOMES:

*class chondrichthynes

*class osteichthynes

Chondrichthyes: Cartilaginous Fishes

-Chondrichthyes consists of sharks, rays, and skates, together with sawfishes and a few dozen species of fishes called chimaeras, or “ghost,” sharks.

-Chondrichthyes are jawed fishes that possess paired fins and a skeleton made of cartilage.

-Most sharks are carnivores that feed on live prey.

-Sharks have well-developed sense organs that aid them in locating prey, including a keen sense of smell and electroreception. 

• Rays and skates comprise more than 500 species and are closely related to sharks. 
• sharks, rays and skates have a cartilaginous skeleton.
• Most species are marine and live on the sea floor, with nearly a worldwide distribution.

Osteichthyes: Bony Fishes

-the Osteichthyes, also called bony fish, are characterized by a bony skeleton. The vast majority of present-day fish belong to this group, which consists of approximately 30,000 species, making it the largest class of vertebrates in existence today.

-A few groups of Osteichthyes, such as sturgeons and paddlefish, have primarily cartilaginous skeletons, but retain some bony elements. 

-bony fish have a lateral line system that detects vibrations in water.

• Bony fish are further divided into two extant clades: Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish).

-Actinopterygii, the ray-finned fish include many familiar fish, such as tuna, bass, trout, and salmon, among others. 

- Sarcopterygii are fleshy and lobed, supported by bone. Early Sarcopterygii evolved into modern tetrapods, including reptiles, amphibians, birds, and mammals.

Actinopterygii and Sarcopterygii