What is a Vertebrate?

Vertebrate Anatomy – Unit 1

FIRST: A Vertebrate is an ANIMAL• What is an Animal?

– KINGDOM Level of Taxonomy– Includes all organisms that possess

the following characteristics:• Multicellular• Heterotrophic• No cell walls around cells• Several other characteristics

SECOND: A Vertebrate is a CHORDATE• What is a Chordate?

– PHYLUM level of Taxonomy– Includes all ANIMALS that possess the

following characteristics:• Dorsal Hollow Nerve Cord• Pharyngeal Gill Slits• Notochord• Post-anal Tail

– A few chordates possess ALL these characteristics at all life stages, but most only possess all of these during EMBRYONIC stages.

THIRD: A Vertebrate is a VERTEBRATE• What is a VERTEBRATE?

– SUBPHYLUM level of Taxonomy• A level not normally addressed in intro bio

classes

– Includes all CHORDATES that possess the following characteristics:

• A BACKBONE that protects the nerve cord and supports the body; replaces the notochord

• This also generally implies the presence of a cranium (skull) to protect the brain.

– Some animals have ONLY the cranium, thus they are not quite true vertebrates

TRUE or FALSE?• All CHORDATES are VERTEBRATES.• All VERTEBRATES are CHORDATES.

The term Chordata comes from• The Notochord

About the Notochord• In a Vertebrate Chordate,

– the Notochord is present only during the EMBRYONIC stages of life.

– The notochord is replaced by the backbone

About the Nerve Cord• Dorsal• Hollow• Anterior end enlarged to create

the BRAIN

Pharyngeal Gill Slits• Pharynx = throat• Present in embryos• These slits in the throat area

become the gills in fish and other vertebrates that breath water

• In mammals and other land vertebrates they become structures of the lower jaw, face and throat.

Other Chordate Characteristics• Closed circulatory system

– Blood always contained in blood vessels

• Muscle blocks or segments called somites in embryos

Who are the Chordates closest relatives?•The closest INVERTEBRATE relative of the chordates are the members of Phylum Echinodermata

–The Sea Stars–The Sea Urchins–The Sea Cucumbers

•How can this be?–The embryonic development of echinoderms has a very important similarity to the embryonic development of chordates, even though the adult forms look very different.

Echinoderms and Chordates•The embryonic opening called a blastopore becomes an ANUS in both echinoderms and chordates.•In all other INVERTEBRATES it becomes the MOUTH.

Phylum Chordata – 4 subphyla• Subphylum Urochordata• Subphylum Cephalochordata• Subphylum Myxini• Subphylum Vertebrata

Subphylum Urochordata•The Tunicates•Also called Sea Squirts•The 4 Chordate characteristics are present in the larval form•The adult looks very different•Larva are free swimming with tails, etc.•Adult is sessile.

Phylum Cephalorchordata•A group called the lancelets•Most common member of this group is amphioxus•Swimmers•Possess all chordate characteristics in adult form

Phylum Myxini•New Phylum •Once thought to be vertebrates, but they do not possess a true backbone – only a true cranium•Hagfish is the only member•Hagfish sliming video

•More slime•More

Subphylum Vertebrata• WE are vertebrates; hence

humans have studied phylum vertebrata a lot.

When did the 1st vertebrates arise on Earth?

•Around 500 million years ago

What were the first vertebrates like?•The first vertebrates were DIFFERENT from vertebrates we know today.•They lacked JAWS.

–Think lampreys which are the only vertebrates that remain today who lack jaws.

•Jawed vertebrates did not appear until around 400 million year ago

•lamprey video•One more

Where did vertebrates first evolve?•Ocean

Defining characteristic of a vertebrate?•Backbone•Though others are discussed.

Vertebrates and sex•All vertebrates have separate sexes – male and female

Some terms with regard to reproduction•Oviparous

–Egg layer–Young are nourished from yolk inside an egg that is laid outside the mother’s body

Some terms with regard to reproduction•Ovoviparous

–Young develop internally, but are nourished with YOLK as though they were inside an egg.–“Live birth”

Some terms with regard to reproduction•Viviparous

–Young develop internally–Nourished directly from the mother’s bloodstream

•NO yolk

–Placenta and umbilical cord involved– icky picture warning…