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Fish Class Agnatha, Chondrichthyes, & Osteichthyes Subphylum Vertebrata ● All vertebrates are divided into two Superclasses ● Superclass Agnatha - Jawless vertebrates (2 living species) ● Superclass Gnathostomata Jawed vertebrates (all other vertebrates) Vertebrate Reproduction ● Oviparous ○ Lay eggs outside the body so they may develop and hatch ● Ovoviviparous ○ Egg remains in mother until offspring hatch ○ The offspring are born alive ● Viviparous ○ Embryo receives nourishment from mother ○ The offspring are born alive Early Amphibian (Ancestor of all Tetrapods) Lungfish Coelacanths Ray-Finned Fish Lobe-Finned Fish Cartilaginous Fish Bony Fish Hagfish & Lampreys Placoderms Ostracoderms Superclass Agnatha ● First appeared in the Cambrian Period about 500 mya ● No jaws ● No paired appendages ● Notochord provides primary protection and support for nerve cord ● Fertilization & development are carried out externally Ostracoderms ● Earliest vertebrates ● Evolved just after the Cambrian explosion ● Jawless - fed by filter feeding ● Covered in armor made of bony plates ● Totally extinct group of fish (P-T extinction) Hagfish and Lampreys Lampreys ● Live mostly in coastal and fresh waters ● Always return to freshwater to reproduce ● Though jawless, the mouth is lined with sharp teeth able to tear flesh ● Ectoparasitic Lampreys ● Begin life as burrowing, toothless larvae ● After 5 to 7 years, they undergo an incredible metamorphosis to turn into pelagic, adult parasites ● Attach to fish, secrete an anticoagulant, and feed on blood Hagfish ● Jaw is partially movable horizontally, but still considered Agnathans ● Entirely marine - never found in freshwater ● Able to change sex to meet population needs - many species exist in a 100:1 female-to-male ratio ● No larval stage Hagfish ● Able to secrete copious amounts of thick slime to deter or evade predation ● Clean off the slime by tying themselves in knots ● Endoparasites - feed by burrowing into the mouth, gills, or anus of a host fish and consuming their prey from the inside out Superclass Gnathostomata ● Jaws ● Paired appendages Early Amphibian (Ancestor of all Tetrapods) Lungfish Coelacanths Ray-Finned Fish Lobe-Finned Fish Cartilaginous Fish Bony Fish Hagfish & Lampreys Placoderms Ostracoderms Class Placodermi ● Among the first jawed fish along with the ancestors of Class Chondrichthyes ● Went extinct along with the Ostracoderms ● Head and thorax were covered by bony plates ● 320 mya fossil shows earliest example of viviparous birth Class Chondrichthyes ● Cartilaginous skeleton ● Notochord provides a large portion of back support ● No operculum ○ Must swim constantly to allow oxygenated water to move across gills ● No swim bladder ○ They are unable to regulate their buoyancy levels Buoyancy ● Cartilaginous fish must also constantly swim to keep from sinking. They use dynamic lift to maintain a constant level in the water column ● Liver oil and the ability of some sharks to swallow air allow them to obtain some level of buoyancy Class Chondrichthyes ● Respire with the use of 5 to 7 exposed gill slits ● Skin covered with dermal denticles - tooth-like structures that protect the skin and cause it to feel like sandpaper when rubbed against the grain ● Denticles also reduce small vortices produced during movement that cause hydrodynamic drag increase swimming efficiency Sharks ● The largest of all fish is the whale shark. It is a filter feeder ● Most sharks are simple carnivores ● Teeth are anchored into flesh rather than bone and they rip out and are replaced very rapidly Shark Anatomy Sexual Dimorphism in Sharks Sharks ● Although most fish are exothermic, the shortfin mako shark and the great white shark are slightly endothermic ● Most sharks are ovoviviparous. They carry their eggs internally until the young hatch and are born alive and fully functional Sharks ● Sharks have electroreceptor organs called the Ampullae of Lorenzini that detect the electromagnetic fields that all living things produce. This assists sharks in hunting and in navigation ● Sharks also have a very keen sense of smell and can detect 1:1,000,000 blood in water Skates & Rays Skates & Rays ● Possess 5 gill slits that are located underneath the pectoral fins rather than on the side of the head as in sharks ● Eggs laid in little pouches you may find on the beach Skates & Rays ● Wide distribution of group members. Tropical to coldwater species exist ● Most are benthic (live on the seafloor) and respire by moving water in through their spiracles towards their gills ● Manta ray is an example of a rare pelagic ray Skates & Rays ·Skates and rays are very similar. However, skates tend to have a more shovel-shaped head than rays and they lack spines in their tails. Early Amphibian (Ancestor of all Tetrapods) Lungfish Coelacanths Ray-Finned Fish Lobe-Finned Fish Cartilaginous Fish Bony Fish Hagfish & Lampreys Placoderms Ostracoderms Class Osteichthyes ● Boney fish - Actually called endochondral bone because it is formed by the ossification of cartilage ● Comprise the most various and largest class of vertebrates on Earth today ● Includes the vast majority of all fish Class Osteichthyes ● Swim bladder present Allows a fish to adjust its buoyancy and thus its position in the water column ● Operculum present - Allows fish to pump water across the gills without having to physically move through the water ● Lateral line – senses vibrations in the water Oxygen Exchange at the Gills Countercurrent Exchange Osteichthyes Evolution Osteichthyes Classification Subclass Actinopterygii ● Ray-finned fish ● Comprised of most members of class Osteichthyes ● Fins attach to body of the fish with multiple, small bones ● All members have homocercal tails Caudal Fins General Osteichthyes Anatomy Subclass Actinopterygii ● Bichirs ● Also known as ropefish ● Live in freshwater environments in Africa and around the Nile delta ● Identified by noting the unique 12+ dorsal fins ● Sister group of all other ray-finned fish Subclass Actinopterygii ● Sturgeon & Paddlefish ● The most ancient living bony fish with shark-like heterocercal tails & partially cartilaginous skeletons ● Sturgeons lack normal scales seen on other bony fish but they have armor plates along their sides ● Paddlefish lack the armor plating but have paddle-like rostrums the detect electromagnetic fields Subclass Actinopterygii ● Gar ● Fresh, brackish, & marine fish of the Americas ● Almost as old and primitive as the sturgeons & paddlefish ● Thicker scales than other bony fish but not as heavily armored as the sturgeons ● Identifiable by noting the long, skinny snout Subclass Actinopterygii ● Bowfin ● Only a single surviving species in this entire family of fish is native to eastern US & Canada ● Closest relative to the teleost fish ● Known for their long dorsal fins that cover most of their back ● Considered a trash fish - not very edible Subclass Actinopterygii ● Teleost Fish ● The most advanced of all fish ● Almost 30,000 species - more than all other vertebrate species combined ● Almost any fish you can name belongs to this group ● Extremely important as food sources for humans and many other animals Subclass Sarcopterygii ● Lobed fins joined to the body at a single bone ● Two dorsal fins with separate bases and diphycercal caudal fins ● There are only 8 living species in this subclass ● ● These include lungfish and coelacanths Subclass Sarcopterygii ● Sauropterygians are able to utilize a primitive lung to breathe air when their ponds dry out or the water becomes anoxic ● Lungfish are known to use their fleshy pectoral fins like legs and crawl to new ponds when their previous ponds dry out Structure of Lungs ● The Trachea leads down to the lung ● Separates into two bronchi leading to each lung ● Tubing terminates into little sacks called ALVEOLI that allow for gas exchange Subclass Sarcopterygii ● ·The subclass split into two main groups long ago with the coelacanths staying in the ocean and the lungfish & tetrapodomorphs moving to freshwater environments ● Tetrapodomorphs further evolved into land vertebrates Fish Scales The End!