BIOL172 Exam 2: Deuterostomia

Deuterostomia

Mouth second

Echinodermata and Chordata

Archenteron (primitive gut tube) opening (blastopore) develops into anus first

Mesoderm develops from endodermal "coelomic pouches"

- fusion forms enterocoelom

Indeterminant cleavage

Why are echinoderms included in the Superphylum Deuterostomia? What kind of symmetry do they feature?

Blastopore becomes anus

Radial cleavage

Enterocoelous coelom formation

Start bilateral symmetry, become radial as adults

Entercoelom

Coelom formed by fusion of coelomic pouches budded from the endodermal lining of the archenteron

Ambulacraria: Echinodermata

Sea cucumbers, sea urchins, sand dollars, brittle stars

Prickly skin

Ossicles: tiny skeletal bones (endoskeleton) covered by epidermis, sometimes form spines: locomotion or defense

Pedicellaria: tiny stalked claws around spines: cleaning, food capture

Pentaradial symmetry

Ambulacral (water vascular) system

Hemal system (nutrient circulation): oral, gastric, and aboral rings

Ambulacraria vs. Chordates

Ambulacraria

- lack true back bone

- Echinodermata and Hemichordata

- radial

Chordates

- have true back bone

- Vertebrates, Tunicates, Lancelets

- notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail

- often cephalization

- bilateral

Chordata

Shared features (synapomorphies)

- notochord

- dorsal hollow nerve cord

- pharyngeal slits

- post anal tail

- endostyle/thyroid gland (secrete iodinated hormones)

- emergence quadrupeds in form of amphibians

- evolution in amniotic egg

Epidermal structures: scales (prevent water loss), claws, hair, feathers (insulation / endothermy)

Vertebrates

Urochordata (tunicates, salps, larvaceans)

Cephalochordata: lancelets

Dorsal Hollow Nerve Cord

Derived from the endoderm

Develops into the brain and spinal cord (CNS) in vertebrates

Notochord

Cartilaginous skeletal rod supporting the body in all embryonic and some adult chordate animals

Post-anal Tail

Locomotion, courting, balance

Reduced in humans and great apes

Contains skeletal and muscle elements

Pharyngeal Slits

Produces thyroid-like hormones

Modified into:

- gill supports or jaw supports in (jawed) vertebrate fishes

- ears, tonsils, and thymus gland (tetrapods)

Cephalochordata

Notochord extends into head

Habitat: sand of warm seas

Suspension feeders

Dioecious: external fertilization

Pharyngeal slits as food particle filters

Atrium: gill chamber, collects filtered water

Urochordata

Tunicates

Tunic: cellulose like CH covers the body

Suspension feeders

Most sessile, salps can swim

Monoecious

Food is filtered by the endostyle mucus

Vertebrata: Craniata

Myxini, Petromyzontia, and Vertebrates

have vertebrae

Vertebrae

bones that form a backbone

Replacement of the embryonic notochord

Amniotes

Eggs with 4 extraembryonic membranes

Yolk sac, amnion, chorion, and allantois

Craniata: Agnatha

Jawless fishes

Lack of jaws

Lack of paired lateral appendages (fins)

Myxini (hagfishes) and petromyzontida (lampreys)

Craniata: Myxini

Eel-like scavengers

Hagfishes

Smile glands (milky mucus)

Cartilaginous skull

Fibrous and cartilaginous skeleton

Notochord persists (not replaced by vertebral column)

Petromyzontida

Lampreys

Sucking mouth with rasping tongue

Craniata: Gnathostomates

Jawed fish + paired fins

Active predation

Chondrichthyes and Osteichthyes

Chondrichthyes

Cartilage fish

Osteichthyes

Ossified / bony skeleton

Actinopterygii (ray finned, bony rays) and Sarcopterygii (lobe finned, fleshy, bones similar to earlier tetrapods)

Amphibians

Frogs, salamanders, and caecilians

Earliest terrestrial tetrapods

Metamorphosis = aquatic and terrestrial phase

Water dependent reproduction

Skin: mucous, moist, permeable

Carnivorous

Amphibians: Urodela / Caudata

Tailed

Internal fertilization

Amphibians: Anura

Tail-less

External fertilization

Amphibians: Apoda

Legless

Caecilians

Nearly blind

internalized fertilization