Lecture 12- Deuterostomes Phyla

Phylum Echinodermata

•  "Spiky-skinned" animals.

Phylum Chordata

• Includes all vertebrate animals, including humans.

Phylum Echinodermata

Synapomorphies:

• Aquatic organisms.

• Bilateral symmetry in larvae; radial (pentaradial) symmetry in adults.

  • Larvae are bilaterally symmetric.

  • Adults are radially symmetric.

• Endoskeleton made of calcium carbonate (CaCO3).

• Water vascular system: A network of fluid-filled tubes and chambers.

  • Water enters through a pore (madreporite).

  • Functions: Movement, respiration (gas exchange), and feeding.

• Tube feet:

  • Enable sea stars to grip prey.

  • Enable feather stars to suspension feed.

• Examples: Sea stars, sand dollars, sea urchins, sea cucumbers.

• Various feeding methods, but all possess a complete digestive tract.

Phylum Chordata

Four Synapomorphies:

All chordates possess these features at some stage of life:

1. Pharyngeal gill slits

2. Dorsal hollow nerve cord

3. Notochord

4. Muscular, post-anal tail

• Some chordates retain these features only in larval or embryonic stages (e.g., gill slits in mammals).

Subphylum Cephalochordata

(Lancelets)

• Adults retain all four chordate features.

• Notochord functions as an endoskeleton for movement.

• ~24 species.

Subphylum Urochordata

(Tunicates)

• Larvae have all four chordate features.

• Adults are sessile; larvae are motile and aid in dispersal.

• Body covered with a polysaccharide "tunic."

• Water enters/exits via siphons.

• Use pharyngeal gill slits for suspension feeding.

Subphylum Vertebrata

(Vertebrates)

• Embryos have all four chordate features.

• Two synapomorphies:

  1. Vertebrae: Column of cartilage/bone along the dorsal side.

  2. Cranium: Protective case for the brain.

• Vertebrates have evolved jaws, limbs, and reproductive modifications (amniotic egg, placenta).

Jawless Vertebrates

 (Agnathans)

• Hagfish: Marine scavengers; lack vertebrae but have a cranium.

  • Produce slime for defense.

• Lampreys: Marine and freshwater ectoparasites.

  • Attach to fish and consume blood.

  • Some are anadromous (migrate to freshwater to breed).

Jawed Vertebrates

(Gnathostomes)

• Have a well-developed cranium and vertebrae.

• Can acquire food by biting, a major advantage in mass feeding.

• Includes bony fishes, sharks, tetrapods (amphibians, reptiles, birds, mammals).

Class Chondrichthyes

(Cartilaginous Fishes)

• Includes sharks, rays, and skates.

• Cartilaginous endoskeleton.

• Evolution of paired fins.

• Some give live birth (unusual for fish).

Class Actinopterygii

(Ray-finned Fishes)

• 27,000+ species.

• Symmetrical tail (unlike sharks’ asymmetrical tail).

• Swim bladder aids in buoyancy.

• Mostly use external fertilization and are oviparous (egg-laying).

Lobe-finned Fishes

Coelacanths & Lungfish)

• Thick, fleshy fins with bones and muscle.

• Lungfish can walk along pond bottoms and breathe using lungs and gills.

Tetrapods

Transition to Land

• Fossil evidence suggests tetrapods evolved from lungfish relatives.

• Tetrapod limbs evolved from ancestral fish fins.

• Land-dwelling vertebrates with four limbs.

Class Amphibia

• Live in aquatic and moist terrestrial habitats.

• Tadpoles undergo metamorphosis into land-dwelling adults.

• Some gas exchange occurs across moist skin.

Amniotes

Evolution of Protective Egg

• Includes reptiles (birds included) and mammals.

• Evolution of the amniotic egg:

  • Protects the embryo from desiccation.

  • Four extra-embryonic layers:

    1. Amnion - Watery cushion.

    2. Yolk sac - Nutrients.

    3. Allantois - Stores waste.

    4. Chorion - Gas exchange.

• Placenta evolved in mammals to provide nutrients inside the mother.

Class Reptilia

(Reptiles & Birds)

• Includes turtles, lizards, snakes, crocodiles, alligators, and birds.

• Adaptations for land:

  • Scaly skin with keratin.

  • Well-developed lungs.

  • Amniotic eggs (leathery or CaCO3 shells).

• Bird adaptations:

  • Endothermic (generate heat metabolically).

  • Flight adaptations: Feathers, hollow bones, keel on sternum, one ovary.

Class Mammalia

(Mammals)

• Hair/fur for insulation.

• Mammary glands produce milk.

• Endothermic.

• Three major lineages:

Monotremes

• Platypuses and echidnas (Australia only).

• Lay amniotic eggs.

• Secrete milk from skin glands.

Marsupials

• Opossums, kangaroos, koalas.

• Young develop in nursing pouch (marsupium).

• Viviparous (give birth to underdeveloped young).

Eutherians

(Placental Mammals)

• Bats, dogs, whales, primates.

• Longer gestation via placenta.

Order Primates

• Monkeys, apes, humans.

• Traits:

  • Forward-facing eyes.

  • Hands for grasping.

  • Opposable thumbs.

  • Large brains and complex social behavior.

Family Hominidae

(Great Apes)

• Orangutans, gorillas, chimps, humans.

• No tail, large bodies.

Genus Homo

(Humans & Extinct Relatives)

• Bipedalism.

• Extremely large brains.

• Extensive tool use.

• Low size dimorphism between sexes.