Chordates and Fish Unit

Learning Target Objectives:•Distinguish between the 3 major chordate divisions and between classes of chordates/fish, listing examples of each.•Compare and contrast features of organisms that make them unique or help place them in a particular class.•Identify body structures (anatomy) and functions (physiology) for each type of vertebrate.•Differentiate between types of births: oviparous, ovoviviparous, and viviparous.

Vocabulary:

Notochord * gill slits * tunicate * lancelet * vertebrate * endoskeleton * axial skeleton * appendicular skeleton * ectothermic * endothermic * cloaca * lateral lines * spiracles * olfactory sacs * viviparous * oviparous * ovoviviparous * rays * operculum * caudal fin * dorsal fin * anal fin * pelvic fins * pectoral fins * pharynx * liver * pancreas * villi * atrium * ventricle * arteries * capillaries * veins * gills * kidneys * bladder * osmoregulation * optic * olfactory * cerebrum * cerebellum * medulla oblongata * swim bladder * external fertilization * milt

Kingdom: Animalia

Phylum: Chordata

At some time in their lives, all chordates show the following characteristics:

1) A notochord – a dorsal rodlike, internal supporting structure (found only in the embryonic stage of vertebrates, later it’s replaced by a backbone)

2) A dorsal, hollow nerve cord

3) Pharyngeal pouches, or gill slits

3 Subphyla:

1) Tunicates (Subphylum Urochordata)

- soft-bodied

- marine (saltwater)

- larva resemble tadpoles, adults are sessile & lose notochord & nerve cord

- filter feeders

Ex: Sea squirts

2) Lancelets (Subphylum Cephalochordata)- Live in shallow warm, marine water- poor swimmers, usually stay mostly buried in sand- Adults show all 3 chordate characteristics- Filter feeders

3) Vertebrates (Subphylum Vertebrata)

- Spinal column of bones (vertebrae) in the advanced stages (beyond embryo) (spinal column of cartilage in sharks)

- Endoskeleton grows with organism- Spinal column surrounds dorsal nerve cord- Dorsal nerve cord swells into a brain at anterior end (cephalization) &

is protected by a skull, or cranium- Axial skeleton (backbone & skull)- Appendicular skeleton – formed where appendages (fins, arms, etc.)

join axial skeleton

Vertebrates (continued)- Heart with 2 to 4 chambers, closed circulatory system, hemoglobin- Coelom contains heart, etc.

Vertebrates may be either:

1) ectothermic – body temperature varies with environment (a.k.a. “cold-blooded”) ecto = outside therm = heat

2) endothermic – fairly constant body temperature (warm-blooded) endo=inside therm = heat

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- Cloaca – a common chamber where the reproductive tract, excretory system, and/or digestive system empty. Therefore only 1 opening is needed to the external world. This is common in vertebrates.

Section 30-1

Muscle segments

TailAnus

Pharyngeal pouches

Mouth

Hollownerve cord

Notochord

Figure 30–1 The Generalized Structureof a Chordate

Section 30-1

Nonvertebratechordates

FishesAmphibians

ReptilesBirds

Mammals

Invertebrate ancestor

Chordate Cladogram

Fish

Subphylum: Vertebrata (have backbones)

3 Classes:

1) Class Agnatha- round, “jawless” mouths- No scales, slimy skin- Notochord present in adults- eel-like shape- Cartilaginous skeleton- Unpaired fins

Ex: lamprey

Lamprey are parasites, drink blood, have no stomach, sucker mouth with teeth, a problem in the Great Lakes, lay eggs in streams – take 3 to 7 years to mature

2) Class Chondrichthyes- Cartilaginous skeleton, NO bones except in jaws on occasion- Paired fins- Good sense of smell- Lateral lines detect vibrations & chemicals- Gill slits- Placoid scales (spiny, like sandpaper) – don’t overlap like fish

scales from other classes of fish- Exs. Include: Rays, Skates, & Sharks- All have a 2 chambered heart

Rays & Skates- Flattened body- Wing-like pectoral fin- Spiracles- openings on top of head let water in for gills- Eat mostly mollusks and crustaceans- Some have poisonous or electrical tails

Sharks:

- Flattened wing-like pectoral fins

- Rows of rotating replacement teeth

- Water entering nostrils does NOT flow to gills, it passes through olfactory sacs used to detect smells. (Because our nostrils are connected to our lungs, we can’t use them for smell under water.)

- Internal fertilization with 3 birth possibilities:

1) Viviparous – young develop in mother & are born alive. Embryo is nourished through a placenta (like humans).

2) Oviparous – slimy eggs are laid shortly after fertilization.

3) Ovoviviparous – eggs remain inside mother,

embryo is nourished by the egg yolk. After

hatching in mom, young are born live.

3) Class Osteichthyes (Bony Fish)

a) Lobe-finned fish have fleshy base to fins/tail; almost extinct Example: Coelocanth

b) Lungfish have lungs to breathe in air AND gills for breathing in water.

c) Ray-finned fish

- Rays = long bones that support fins.

- Scales overlap each other

Examples within this group: eels, seahorses & most all other fish

Fish Anatomy (structure)

Operculum – hard covering over gills at back of head region. Water enters mouth, flows over gills, exits

out back of operculum.

Fins:

Caudal fin – tail fin, moves side-to-side

Dorsal Fins (usually 2) – are on top of fish’s back; the front fin is the anterior dorsal fin, the back fin is the posterior dorsal fin (posterior dorsal fin has rays-other fin has spines)

Anal fin – on ventral surface (helps keep fish upright and moving in straight line)

Pelvic fins (paired) – found behind (“posterior to”) & below (“ventral to”) the pectoral fins

Pectoral fins (paired) – located on sides of body just posterior to the operculum

Internal Anatomy:

Digestive system: Mouth pharynx (throat cavity) esophagus stomach intestine anus

Liver – makes/secretes bile (aids digestion, especially of fats) (gallbladder stores bile)

Pancreas – secretes insulin (regulates blood sugar) and digestive enzymes

Villi – projections of the intestinal wall that increase surface area for better nutrient absorption

Section 30-2

Muscle

Kidney

Vertebra

Stomach

Pyloriccecum

Swimbladder

Esophagus

Spinalcord

GillsBrain

Urinarybladder

Anus

Reproductiveorgan

Intestine

Pancreas

Liver

Gallbladder

HeartOperculum

Mouth

Figure 30–11 The Anatomy of a Fish

Circulatory System2 heart chambers:

1) Atrium – receives blood from body

2) Ventricle – pumps blood to body

Arteries carry blood from heart to gills & other body organs. This blood is high in oxygen after leaving the gills so it is bright red.

Capillaries – small blood vessels where oxygen is exchanged with carbon dioxide (CO2). (Oxygen is taken in and carbon dioxide is released by cells back into the bloodstream)

Veins – carry blood from organs back to heart

Excretory System (removes liquid & nitrogenous waste)

Gills release nitrogen wastes in the form of ammonia (Gills are also part of the respiratory system)

Kidneys concentrate liquid nitrogenous wastes in urea, then pass it to the bladder where it’s stored until release, passing to a cloaca (combination of urinary tract just before urogenital opening) and out an opening behind the anus.

Gills & kidneys also release excess salt or water for fish osmoregulation.

Ventral view: Pectoral fin pelvic fin anus urogenital opening

anal fin

Nervous SystemBrain & spinal cord

Brain = 5 paired lobes:

- optic lobes – largest lobes, located toward middle of brain, receive impulses from eyes (sight)

- olfactory lobes – furthest anterior lobes, used for smell

- cerebrum – just anterior to optic lobes, center for instinct & intelligence

- cerebellum – just posterior to optic lobes, used for muscle coordination

- medulla oblongata – controls internal organs cerebrum

Swim Bladder – thin walled sac filled with air to control the fish’s depth in water. Not present in sharks!

Reproductive System- External fertilization usually; some fish, such as guppies

& mollies, bear live young & fertilization is internal.- Separate sexes- Male testes produce sperm (milt)- Female ovaries produce eggs- Sperm & eggs are released through urogenital opening

during external fertilization