Gnathastomes (jaw mouth)

  • Have true, hinged jaw

  • Extremely novel trait!

  • Can not chew/rotate

  • Allows for biting, grasping and tearing food

  • Bigger bites > increased food ingestion > more energy available > larger body, faster speed, etc.

  • Have paired pectoral fins and paired pelvic pins (anal fins)

  • Balance and quick turns

  • These two novel traits allowed fish to become active feeders

  • Less turbulence in water

  • Two classes: Chondrichthyes (cartilaginous) and Osteichthyes (bony)

Class Chondrichthyes

  • Almost marine species

  • Cartilaginous bone, jawed fish

  • Endoskeleton composed of cartilaginous bone

  • Dorsolaterally flattened, sleek fusiform bodies

  • They are generally fast, active swimmers

  • Almost exclusively carnivorous but some are filter feeders

  • Intestine has spiral valve that slows food passage

  • Allows greater absorption of nutrients

  • Have rectal gland that secretes high concentration of sodium chloride

  • Helps kidneys with osmoregulation

  • Pulls salt out from blood, released in feces

  • Have placoid scales (cut)

  • Teeth evolve from placoid scales

  • Scales do not grow as animal grows; animals produce more scales

  • Their cartilaginous bodies are denser than water

  • Have large livers that contain bouyant oils, less dense than water

  • Large pectoral fins provide lift

  • Have heterocercal caudal (tail) fin

  • Not same length, more mass above backbone

Well-developed sensory system:

  • Excellent eyesight but colorblind

  • some have binocular vision (cant see them in front of them)

  • Acute sense of smell

  • Two nares/nostrils under the snout

  • Water flows into each nostril, through nasal sac and then out of nostril

  • Inside of nostril line with olfactory epithelium cells

  • Ampullae of Lorenzini allow for rapid electromagnetic field detection

  • Pores in on the head and ventral side

  • Each pore connects gel-filled cells that detect electric fields

  • Lateral line to detect water motion

  • Receptors are same as hair cells found in ears of terrestrial animals

  • Cilia bend in response to changes in water pressure

  • Sense vibrations ā€œhearingā€

  • Smell is used first]

  • Hunt/bite through lateral line, ampullae

  • Additional eyelid is used to cover for protection when biting

Respiratory System: Gills

  • Thin tissues filaments with extensive folding

  • Increased surface area ensures that enough oxygen can be absorbed from water

  • All water contains dissolved oxygen

  • Remember, diffusion occurs from high concentration to low concentration

  • Blood and water move in counter-current

  • Oxygen-poor blood flows countercurrent to the flow of water across gills

  • Although dissolved oxygen is in low concentration in water, it is at a much higher concentration than the oxygen-poor blood.

  • Therefore, oxygen diffuses from water into the blood

  • Carbon dioxide is removed in the opposite way: carbon dioxide diffuses from high concentrations in the blood to low concentration in the water

Reproduction:

  • Sexual reproduction with internal fertilization

  • Males have claspers (penis)

  • During reproduction, the male inserts one clasper at a time into the female. Muscles push sperm into female oviduct.

  • Chondrichthyes produce relatively few offspring at a time

  • No parental care provided offspring

Offspring development:

Oviparous:

  • All skates, some sharks

  • Females lay fertilized eggs. Embryo receives nutrition from egg yolk

  • Eggs covered in leathery case

Viviparous:

  • All rays, most sharks

  • Egg sac with embryo attaches to motherā€™s oviduct and embryo gets nutrition from mother

  • Live birth

  • Most are a special type of viviparous, called ovoviviparous

Ovoviviparous:

  • Fertilized eggs develop in mother, embryo receives nutrition from egg yolk, hatch and develop in utero, mother gives birth live.

  • Some species, young cannibalize each other

  • Relative fitness of mother increases, extra nutrients, how to hunt, safety, bigger and smarter.

Subclass Elasmobranchii (Only sharks)

  • Holocephali is a second subsclass that includes chimeras

  • Shark mouth armed with rows of serrated, pointed enameled teeth.

  • Phosphatized mineralization

  • Teeth in the first row are the current functional teeth

  • Replacement teeth behind first row

  • Never run out of teeth

Superorder Batoidea (rays)

  • Mostly bottom-dwellers

  • Have spiracles (behind eyes) that allow them to bury in the sand and still breathe

  • manta rays, devil rays, are extremely large and are pelagic

  • Mostly filter feeders

  • Pectoral fins are enlarged and fused with the head

  • Pectoral fins provide propulsion/thrust

  • Caudal fin is adapted into a whip-like tail with jagged edge and sharp spine with venom glands (at least one barb)

  • Used for defense- they lash/puncture

  • Teeth are modified into flatten, spiky bars that crush (exoskeleton)

  • Eat crustaceans, molluscs, small fish (mostly sessile prey)

  • Like sharks, they continuously replace teeth

Class Osteichthyes

  • Osseous bone, jawed fish

  • Have endoskeleton made of osseous bones

  • Both marine and freshwater species

  • General body shape: laterally flattened

  • Have overlapping teleost scales

  • The scales grow larger as the fish grows larger

  • Bigger fish have bigger scales

  • Carnivorous, herbivores, and omnivorous

  • Their osseous bodies are denser than water

  • Swim bladder to control buoyancy

  • Gas enters swim bladder from digestive system or from blood

  • More gas= greater buoyancy, less gas = reduced buoyancy

  • Scales wont cut

Well-developed sensory system:

  • Excellent eyesight, most see color

  • Shallow water species see more color

  • Acute sense of smell

  • Same as Chondrichthyes

  • No ampullae of Lorenzini

Osteichthyes Subclasses

Actinopterygii

  • Predominant subclass

  • Ray-finned fish

  • Have long, thin endoskeletal bones in fins

  • Muscles that move the fins are located in the body

Sarcopterygii

  • Only a few extant species, very ancient

  • Lobe-finned fish (bendy)

  • Have short, fleshy fins with thick bones and muscle in fins

  • Thought to have given rise to terrestrial tetrapods

  • Move one pod to another by walking

Reproduction:

  • Almost exclusively external fertilization via courtship spawning

  • Embryos develop within the egg

  • Spherical shaped eggs with yolk for nourishing embryo

  • Some species guard their eggs, most do not

  • No parental care

  • Sea horses are an example of internal fertilization

  • Ovoviviparous

  • Females lay her eggs in maleā€™s pouch, he releases sperm into the pouch

  • Embryos develop within the egg, inside the fatherā€™s pouch

  • When the embryos hatch the father releases them from his pouch

  • He provides protection to newly hatched offspring

  • Can also come back to the pouch

  • Leafy dragon fish

Circulatory System

  • 2 chambered heart

  • One atrium and one ventricle

  • Only deoxygenated blood in the heart

  • Single circuit: blood flows from heart to gills to body, back to heart

  • Deoxygenated blood from body enters atrium, flows from atrium into ventricle. Ventricle pumps blood to gills where it is re-oxygenated (gill circulation). Blood flows from gills to body then returns back to atrium, deoxygenated. systematic circulation.

  • Heart squeezes by water pressure to pump