Lec 34: Vertebrates

Chordates

bilateral animals, belong to a clade known as deuterostomia

• has a spine

• one-way gut

• triploblastic

four key characteristics of chordates

• notochord

• dorsal, hallow nerve cord

• pharyngeal slits or clefts

• muscular, post- anal tail

Notochord

• longitudinal, flexible rod between digestive and nerve cord

• provide skeletal support

Dorsal, hallow nerve cord

• develops from a plate of ectoderm that rolls into a tube dorsal to the notochord

• nerve cord develops into the central nervous system: the brain and spinal cord

Pharyngeal slits or clefts

• suspension-feeding structures in many invertebrate chordates

• gas exchange in vertebrates

• develop into parts of the ear, head, and neck in tetrapods

Post-anal tail

• the tail contains skeletal elements and muscles

• provides propelling force in many aquatic species

Lancelets

• example

• bladelike shape

• marine suspension feeders

• have characteristics of chordate body plan

Tunicates - Urochordata

• marine suspension feeders, sea squirts

• closely related to chordates

• Larvae- free-swimming, non feeding

• adult- only have pharyngeal gill slits

Derived characters of vertebrates

• vertebrates enclosing a spinal cord

• an elaborate skull

• fin rays in aquatic forms

Lampreys

• oldest living lineage of vertebrates

• jawless vertebrates

• inhabit marine and freshwater habitats

Origins of bone and teeth

• mineralization originated with vertebrate mouthparts

• jawed vertebrates or gnathostomes

Gnathostomes

• additional duplication of Hox genes

• enlarges forebrain, enhance smell and vision

• in aquatic, the lateral line system = sensitive to vibrations

Chondirchthyans

• have a skeleton composed primarily of cartilage

• largest and diverse group

• include sharks, rays, and skates

Shark egg fertilize

• Oviparous: egg hatch outside the mother’s body

• Ovovivparous: the embryo develops within the uterus and is nousidhed by the egg yolk

• Vivparous: the embryo develops within the uterus and is nourished through the yolk sace placenta from the mother’s blood.

Osteichthyes

• bony fish and tetrapods

• have bony endoskeleton

• fishes breathe by drawing water over gills protected by an operculum

Tetrapods

• four limbs and feet with digits

• ears for detecting airbone sounds

Amphibians

• “both ways of life” not good, limited to both

• represented about 6,150 species of organisms in three orders

• skin that complements lungs for gas exchange \

• fertilization by eggs

Amniotes

• are tetrapods: reptiles, birds and mammals

• amniotic egg= contains membrane that protect embryo

• extra embryonic membranes are the amnion chorion yolk sac and allantois

Reptiles

• includes tuataras, lizards, snakes, turtles, crocodilians, birds, extinct dinosaurs

• have scales for waterproof

• are ectothermic, absorbing body heat

• birds are endothermic, keeping body warm through metabolism