evolution and classification of fishes
DESCRIPTION
Evolution and Classification of Fishes. Morphology of the Bony Fish. Classification. Subphylum: Vertebrata (45,000 species) -Class: Agnatha~jawless fishes (hagfish, lampreys) *May also be divided into: -- Class: Myxini (hagfish) - PowerPoint PPT PresentationTRANSCRIPT
Morphology of the Bony Fish
ClassificationSubphylum: Vertebrata (45,000 species) -Class: Agnatha~jawless fishes (hagfish,
lampreys) *May also be divided into: -- Class: Myxini (hagfish) -- Class: Cephalaspidomorphi (lamprey)Class: Chondrichthyes ~ sharks, skates, raysClass: Osteichthyes (Actinopterygii) ~ bony fishes- Class: Sarcopterygii ~ lobe-finned fishes *lungfishes (ancestors of amphibians) and coelacanths
AdaptationsBuoyancy: trap gas inside body in order to control vertical position in waterStreamlined shapeMuscular tailPaired finsMucus secretionsHighly developed senses of smell and touchLateral line system: detects vibrations
EvolutionAll classes of fishes appear to have arisen from the
jawless ostracoderms (small fish covered with bony plates) 500 million years ago – only vertebrates for 50 million years! By ~350 mya, most became extinct; survivors became ancestors of jawless fishes.
First fishes to have paired fins and jaws were the acanthodians (spiny fishes) – became extinct 270 mya.
Relatives of modern jawed, bony and cartilaginous fishes began to appear in the fossil record 400 million years ago.
EvolutionTwo adaptations seem critical to the
evolution of other vertebratespouch in the posterior portion of the mouth
that functioned as a lung (lungfish)emergence of fins supported by bony lobes
projecting from the body (lobe-finned fishes) ancestors of amphibians, as lobes evolved into
appendages and allowed for terrestrial living
Agnatha – 80 speciesCyclostomes, or “round mouths”Slimy skin with no plates or scalesNotochord (dorsal nerve cord)Eel-like shapeCartilaginous skeletonUnpaired finsMarine or fresh water
Agnatha, cont.Lampreys (Cephalaspidomorphi):
Most are parasitic, sucking blood and body fluids of other fish ~ highly developed sense of smell toothy tongue tears hole in fish; chemical is released to
prevent fish’s blood from clotting -- NO STOMACH
Hagfish (Myxini):Bottom dwellers in cold marine watersScavengers of dead and dying fish on ocean bottomSaws hole in fish with toothed tongue and eats
them from the inside out – enters through gills, skin, or anus.
- No vertebrae, but do have a cranium and an endoskeleton
ChondrichthyesMovable jaws and cartilaginous skeletons800 species of sharks, skates, and rays living
in salt waterMost are carnivores with large olfactory
organs and lateral line systems to track preySkin covered with placoid scales (small,
toothlike spines that feel like sandpaper)
SharksSwim w/ side-to-side motion of asymmetric tail
finsPaired pectoral fins behind head jut out from
the body like wings of an airplaneMouth has 6 to 20 rows of backward-pointing
teeth that can be replaced ~ one shark may use more than 20,000 teeth
SharksAcute ability to detect chemicals ~ blood from an
injured animal can be detected up to 500 m away!Well-developed lateral line systemMust swim continuously for gas exchange to occur
(Water… Mouth… Gills… Gill slits)Eggs are fertilized internally and pups are born
aliveMale grasps female with modified fins called
claspersSperm runs from male into female through grooves
in the claspers
Rays, Skates, and RatfishesFlattened bodies with winglike, paired
pectoral fins and, often, whiplike tailsRays: diamond- or disk-shaped bodiesSkates: triangular bodies
Bottom dwellersWater enters gills through two spiracles
atop their heads Most feed on mollusks and crustaceans25 species of ratfishes (chimaeras)
Osteichthyes95% of 24,000 fish speciesBony internal skeleton, scaly skin, sense
organs, fins, and diverse reproductive patternsLobe-finned fishes - (1 species - coelacanth) * Lungfishes (6 species left today) * Coelacanth (1 species left today)Ray-finned fishes ~ snake-like eels, yellow
perch, cave fish, herring, carp, walleye, etc.!!
Morphology of a Bony Fish
Anterior- Head EndPosterior- Tail EndDorsal- Top side, back bone sideVentral- Underside, belly side
External AnatomyOperculum: covers and protects the gillsCaudal fin: moves from side to side for swimmingAnterior dorsal fin (spines), posterior dorsal fin
(rays), & anal fin: keep fish upright and moving in a straight line
Pelvic fins & pectoral fins: used to steer, brake, move up and down, and move backwards
Lateral Line: Sensory cells that help fish sense vibrations and movement in the water.
***Fins are richly supplied with blood and help the fish to regulate body temperature when they are moved up or down
External Anatomy, cont.Integument (skin): covered with round scales
of modified bone Grow throughout life, creating growth rings
that allow the age of the fish to be determined
Chromatophores: pigmented cells that give the fish color pattern
Internal AnatomyDigestive System
Carnivores with sharp teeth pointing inwardAnchored tongue lined with nerve cells for
chemical detectionMuch digestion occurs in outpockets of the
stomach called pyloric cecaLiver and pancreas secrete digestive
enzymesIntestine has fingerlike extensions called villi
to increase surface area available for digestion
Internal Anatomy, cont.Circulatory System
Adapted for rapid swimmingTwo-chambered heart, blood vessels, and
blood with red and white blood cellsOxygenated blood is carried by arteries and
capillaries from gills to rest of the bodyDeoxygenated blood is carried by veins from
the body to the gills
Internal Anatomy, cont.Respiratory and Excretory System
Gills consist of four sets of curved pieces of bone
Each gill has a double row of gill filaments richly supplied with capillaries for rapid gas exchange
Gills help kidneys in excretion of nitrogenous wastes from the body; both organs function in osmoregulation (maintaining proper salt balance) freshwater fish need salt and, therefore, must
excrete excess water in order to maintain internal homeostasis
Internal Anatomy, cont.Gas Bladder (Swim Bladder)
Contains a mixture of oxygen, carbon dioxide, and nitrogen obtained from the bloodstream
By regulating the amount of gas in the sac, fish adjust overall density and, thus, move up or down in water or hover at a given depth
Internal Anatomy, cont.Nervous and Sensory System
Brain, spinal cord, and nervesBrain consists of five paired lobes
Optic lobes (largest part of brain): sight Olfactory lobes: respond to smells Cerebrum: respond to smells Cerebellum: coordinates the muscles Medulla oblongata: regulates internal organs
Internal Anatomy, cont.Reproduction
Separate sexes (dioecious)Perch: external fertilization (eggs hatch within a
few hours in warm water, many weeks in cold) Sperm from male is contained in a fluid called milt 80 to 3 million eggs may be laid, depending upon species
Some fishes bear live young after internal fertilization, e.g., guppies and mollies
Spawning: various patterns depending upon species