KINGDOM ANIMALIA – CHORDATES

1. Phylum Chordata• Organisms that belong to the phylum Chordata are called chordates.• All chordates have, at some point in their life cycle, the following characteristics:

◦ Notochord: Long, supporting rod that runs through the body just below the nerve chord.▪ Most chordates only have a notochord as an embryo.▪ Replaced by the backbone in vertebrates.

◦ Dorsal Hollow Nerve Chord:▪ Runs along the back (dorsal) part of the body.▪ Nerves branch off of this chord and connect to various parts of the body.▪ Develops into the spinal cord in many species.

◦ Post-anal Tail: Tail that extends beyond the anus▪ Can contain bone and muscle.▪ Used in swimming in many aquatic species.

◦ Pharyngeal Gill Pouches: Structures in the throat region▪ In some species these pouches develop into the gill slits.▪ In other species (such as humans) they develop into parts of the ear, face and throat.

2. Chordate Classifications• Subphylum Tunicata• Subphylum Cephalochordata• Subphylum Vertebrata

◦ Class Agnatha (Jawless fish)◦ Class Chondrichthyes◦ Class Osteichthyes◦ Class Amphibia

◦ Class Reptilia◦ Class Aves◦ Class Mammalia

3. Subphylum Tunicata• Named for the tough tunic that surrounds the adult.• Even though the adults don't much resemble an animal, they are actually very closely related to the

vertebrates.• As adults they are sessile, filter feeding organisms that live either in solitary or in colonies. • The larval stage is tadpole-like and possess all four characteristics that define chordates

(notochord, nerve chord, pharyngeal pouches, post-anal tail).◦ There is a type of tunicate that is tadpole-like throughout its life cycle.

▪ It is thought that vertebrates evolved from something like this tadpole-like adult tunicate.

4. Subphylum Cephalochordata• The cephalochordates are the lancelets, which are small (3-7 cm long), aquatic, fish-like animals

that lack a distinct head and have no cranium.• They use their tentacles to help filter food from the water.• Lancelets are interesting because they display the basic chordate characteristics in a simple and

obvious form (due to their transparency).

5. Subphylum Vertebrata• General Characteristics:

◦ Backbone (vertebral column)◦ Exhibit cephalization◦ Gaseous exchange in gills and lungs

◦ Two pairs of limbs◦ One pair of image forming eyes◦ Separate sexes

6. Temperature Regulation• Ectothermic (Poikilothermic): These organisms do not produce their own heat. They control their

internal temperature by absorbing heat from the environment.◦ They are 'cold blooded.'

• Endothermic (Homeothermic): These organisms maintain a constant internal temperature, regardless of the outside environment, by using heat released during metabolic processes.◦ They are 'warm blooded.'

7. Class Agnatha• Jawless Fish (Agnatha means “No jaw”)• Most primitive of the vertebrates• Ectothermic• Long cylindrical bodies with cartilage skeletons• Lack paired appendages• 60 species of two general types:

◦ Hagfish▪ Scavengers that bore into the bodies of dead or dying fish.

◦ Lamprey▪ Parasitic bloodsuckers

• Attach to fish with their teeth and use their rasping tongue to file away the skin and suck out blood.

• Fish will typically die due to blood loss and infection of the wound.▪ There is justice in this world though:

• Lampreys are only able to reproduce once because after they lay their eggs, their reproductive canal remains open which allows a fungus to infect it, causing its subsequent death.

8. Evolution of the Jaw• Gill arches gradually changed into jaws• The evolution of the jaw is an important step in fish evolution because it allowed fish to be able to

ingest a much wider variety of foods and to begin an active hunting life style as opposed to being apassive filter feeder or parasite

9. Class Chondrichthyes• Cartilaginous fish• Endoskeleton made out of cartilage reinforced with calcium

◦ Cartilage is lighter and more flexible than bone which allows them to float and be more agile• About 900 species• Evolved 400-450 million years ago• Examples: Sharks, rays, skates & ratfish

10. Chondrichthyes Characteristics• Well-developed jaws• Highly developed sense organs• Pectoral and pelvic fins• Rostrum: Snout that overhangs the mouth• Internal Fertilization• Tough skin plates (small tooth-like structures with the same internal anatomy of teeth)• Teeth that are continuously replaced

◦ The teeth and plates of sharks are thought to be evolutionarily related

11. Chondrichthyes Feeding Habits• Sharks are carnivorous hunters feeding off of fish & seals• Because of their diet, sharks have a unique digestive feature called the spiral valve.

◦ It is a spiraling flap of absorptive tissue which increases the surface area of the intestine◦ Sharks swallow large chunks of food and the spiral valve slows the movement of food; this

gives the enzymes time to work• Basking & whale sharks and manta rays, are filter feeders that feed off of mostly plankton• Skates eat mollusks, crustaceans and worms

12. Cloaca• Cloaca: Posterior cavity that receives the ducts of the urinary, digestive and reproductive systems• AKA: Nature's mixing bowl

13. Buoyancy & Swimming• Sharks are very streamlined, but are heavier than water (because they lack a swim bladder) and

will sink if not swimming forward.• Sharks increase their buoyancy by having a large oil-filled liver that reduces their density, but not

enough to prevent them from sinking.• Sharks must also continually swim in order to move water over their gills. They lack the necessary

mouth muscles that fish use to suck water over their gills.

14. Shark Reproduction• Oviparous: Egg laying (eggs laid in cases)

◦ Dogfish, catshark, various skates & rays• Ovoviviparous: Retain fertilized eggs which hatch within the uterus

◦ Most sharks are ovoviviparous• Viviparous: Young develop in the uterus

◦ Very rare: Hammerhead sharks & bull sharks

15. Class Osteichthyes• Bony Fish• Fins are finer and provide greater maneuverability• Operculum: allows fish to suck water over their gills• They have an air bladder that allows for the fish to remain stationary at any depth• Their body is covered with flattened scales. The skin contains numerous mucous glands which

makes the fish slimy• Most are oviparous• Ectothermic

16. Types of Bony Fish• Ray-Fin Fish: tuna, bass, salmon• Lungfish:

◦ They can get up to 90% of their oxygen from the air if necessary◦ This can be very important as many of these fish live in areas prone to drought

• Lobed-fin fish:◦ This entire group was though to be extinct until the 1930s when a live one was found

▪ Named Coelacanth◦ Has a bizarre swimming style which consists of walking-like movements of the paired fins

▪ No side to side beating of the tail as in most fish◦ This species is extremely important since they are the source of the first land vertebrates

▪ Fins evolved into legs/feet of land animals

17. Evolution of Land Animals• It is thought that the ancestors of land animals started using the land as an escape from predators• Another idea is that, since at around the time of land animal evolution the oceans were very

conducive to fish, there were too many fish offspring in the water and that many were drawn to theland in order to utilize the as yet unexploited food sources

18. Evolution of the Lung• The lungs evolved from a pouch of the esophagus that was used as a swim bladder in some fish.• In fact, the lungfish uses that pouch as its lung to absorb oxygen from the air.• This “lung” in lungfish is very rudimentary retaining swim bladder features and doesn't have the

elaborate folds to increase surface area for gas exchange that higher animals have.

19. Class Amphibia• Live on both land and in the ocean (“Amphibia” means “both life”)

◦ Have terrestrial and aquatic adaptations• They have moist and highly vascularized skin.

◦ Their skin is the most important organ of respiratory exchange despite the presence of lungs◦ Lungs are quite rudimentary, still retaining swim bladder features and lacking alveoli (folds)

• Ectothermic• Still tied to water for respiration and reproduction:

◦ Nearly all reproduce and develop in aquatic habitats▪ Most frogs and toads are external fertilizers (salamanders are internal fertilizers)

◦ Most are oviparous, though some are viviparous and ovoviparous◦ Amplexus (Latin for “embrace”): Male grabs the female as if they were copulating, but the

male releases his sperm as the female releases her eggs

20. Class Reptilia• 7,000 species• Conceived, live and die on land• Needed to adapt specialized organs for land survival

◦ Their skin is dry with protective keratin scales▪ This reduces water loss

◦ Retained cloaca, but the male has a penis for copulation and internal fertilization (water not required)▪ Egg laying was brought to land▪ The eggs are porous, leathery and contain food and fluids

21. Reptilian Traits• Uses kidneys to convert nitrogen wastes to uric acid (this preserves water)• Lungs are less swim bladder like with more alveoli• Most are carnivorous

◦ Locate food by sight, heat detecting, olfactory and hearing• Ectothermic

◦ Do not use metabolism to regulate heat; this conserves energy

22. Crocodile vs. Alligator (not a fight to the death)• Crocodiles have a very long, narrow, V-shaped snout, while alligators have a wider, U-shaped

snout• Crocodiles have upper and lower jaws that are nearly the same width, so the teeth are exposed• Alligators have a wider upper jaw, so when the mouth is closed the teeth in the lower jaw fit into

sockets of the upper jaw, hidden from view so that only the upper teeth are exposed

23. Class Aves• 8,600 species• Light skeleton (many bones are hollow)• Feathers made out of keratin

◦ Evolved from reptilian scales◦ Feathers are strong for their weight due to interlocking barbs

• Lack urinary bladder, solid waste and liquid waste are added together• Endothermic: Allows them to adapt to many different environments

24. Class Mammalia• Hair made of keratin• Heterodonts: Have differently shaped teeth• Sweat and scent glands

◦ Improved sense of smell due to larger nasal cavity• Endothermic• Reproduction & Development

◦ Internal fertilization ◦ Internal development (except for monotremes)◦ Females have separate urinary and reproductive tract◦ Feed their young with milk made in mammary glands

25. Oviparous Mammals• 5 species in the order Monotremata

◦ Four species of echidna and one species of the duck-billed platypus• All live in Australia or New Guinea• Lay eggs, but have hair and nurse young

26. Marsupial Mammals• Fetuses do not fully implant in the simpler uterus• Adult females have a belly pouch (marsupium)• Newborns stay inside, attached to a nipple, for months• Examples: Possum, kangaroo, koala bear

27. Placental Mammals• Grow embryos in uterus• True placenta formed by fetus and mother

◦ Joins the embryo to the mother within the mother’s uterus◦ Embryo is nurtured by blood from the mother

• 95% of all mammals