Chordates Part 2: Origins and Evolution of Jawed Vertebrates
Intro- relationships of major vertebrate groups
Diversity is uneven: Some
groups are extremely successful,
others are not. Some, like lampreys, may never have
been diverse. Others, like coelacanths, are relicts of
groups that were once more successful.
o Coelacanth – 2 species
o Lungfish – 6 species
o Lamprey – 40 species
o Hagfish – 60 species
o Sharks and kin – 1050 species
o Ray-finned fish – 30.000 species
o Tetrapoda – 30,000 species
Agnatha – Jawless fish
Hagfish (Myxini)
o Blind, eel-like fish. Have a dorsal and ventral fin
like advanced fish, but lack either jaws or eyes.
Have a cartilaginous skull (cranium) but uniquely
among vertebrates, no vertebrae.
o Deep water scavengers: hagfish tend to live in
cold, dark environments where the lack of eyes
isn’t an issue. The eel-like body and lack of bones
, allow them to slither inside carcasses of dead fish
& whales and devour them.
o Lack true jaws, but the tongue bears toothlike
spines that can close like a book to seize
meat/prey
o Can tie themselves in knots - then work the knot
down the body to rip off flesh
o Also have the ability to absorb food through the
skin, like a tapeworm. Can simply burrow inside a
dead animal and feed by osmosis
o Slime Eel: rapidly secrete proteins that create a
thick mucus/slime as a defence – sharks attempt to
bite hagfish but back off after slime clogs their
mouths & gills
o Hagfish thrive on adversity and have survived
multiple mass extinction events with minimal
changes to their form/ecology – Myxinikela, a 300
million year old hagfish
Lampreys
o Like hagfish, have a long, slender body with a
dorsal and ventral tail fin, and a cartilage skull.
o They are more sophisticated than hagfish in 2 ways
– they have vertebrae and eyes.
o Lampreys have long been classified as vertebrates,
and the simpler hagfish has been classified as
craniate – almost but not quite a vertebrate
o Larval lamprey look and live a lot like Amphioxus –
they are filter feeders that bury their bodies in the
sand and stick their heads out to filter-feed. Can
also see the chordate groundplan – muscle bands,
post-anal tail, nerve cord, notochord, etc.
o Parasites – lampreys have a sucker-like oral disk
armed with spines that they can use to attach to
Intro- relationships of major vertebrate groups
Diversity is uneven: Some
groups are extremely successful,
others are not. Some, like lampreys, may never have
been diverse. Others, like coelacanths, are relicts of
groups that were once more successful.
o Coelacanth – 2 species
o Lungfish – 6 species
o Lamprey – 40 species
o Hagfish – 60 species
o Sharks and kin – 1050 species
o Ray-finned fish – 30.000 species
o Tetrapoda – 30,000 species
Agnatha – Jawless fish
Hagfish (Myxini)
o Blind, eel-like fish. Have a dorsal and ventral fin
like advanced fish, but lack either jaws or eyes.
Have a cartilaginous skull (cranium) but uniquely
among vertebrates, no vertebrae.
o Deep water scavengers: hagfish tend to live in
cold, dark environments where the lack of eyes
isn’t an issue. The eel-like body and lack of bones
, allow them to slither inside carcasses of dead fish
& whales and devour them.
o Lack true jaws, but the tongue bears toothlike
spines that can close like a book to seize
meat/prey
o Can tie themselves in knots - then work the knot
down the body to rip off flesh
o Also have the ability to absorb food through the
skin, like a tapeworm. Can simply burrow inside a
dead animal and feed by osmosis
o Slime Eel: rapidly secrete proteins that create a
thick mucus/slime as a defence – sharks attempt to
bite hagfish but back off after slime clogs their
mouths & gills
o Hagfish thrive on adversity and have survived
multiple mass extinction events with minimal
changes to their form/ecology – Myxinikela, a 300
million year old hagfish
Lampreys
o Like hagfish, have a long, slender body with a
dorsal and ventral tail fin, and a cartilage skull.
o They are more sophisticated than hagfish in 2 ways
– they have vertebrae and eyes.
o Lampreys have long been classified as vertebrates,
and the simpler hagfish has been classified as
craniate – almost but not quite a vertebrate
o Larval lamprey look and live a lot like Amphioxus –
they are filter feeders that bury their bodies in the
sand and stick their heads out to filter-feed. Can
also see the chordate groundplan – muscle bands,
post-anal tail, nerve cord, notochord, etc.
o Parasites – lampreys have a sucker-like oral disk
armed with spines that they can use to attach to
