Chordates

Unique characteristics of chordates

Dorsal nerve cord
Notochord
Pharyngeal pouches/slits
Post

Dorsal hollow nerve cord

becomes the central nervous system

Notochord

Flexible, dorsal rod
Axis for muscle attachment

Pharyngeal slits

Opening of pharyngeal cavity
Adapted for feeding/ respiration

Endostyle

Gland associated with pharyngeal slits
Produces mucus to trap food particles

Muscular post

anal tail

Chordate classification

Early and advanced

Early chordates

Cephalochordata and urochordata

Advanced chordates (vertebrates)

Craniata

Cephalochordata

Lancelets/ amphioxus
Have all 4 characteristics
Live on sandy seafloors

Cephalochordata movement

Use their notochord and segmented muscles

Cephalochordata feeding

Mouth pulls in water
Goes through pharyngeal slits
Food trapped by mucus
Water goes to atrium and out

Urochordata (tunicates, sea squirts)

Look like barrels and have prominent brachial basket
Most are solitary, some colonial

Urochordata larva

All 4 characteristics

Urochordata adult

Gill slits remain
Notochord and tail disappear
Nerve cord becomes reduced

Adult tunicates feeding

Water circulation
(Incurrent siphon, pharynx, atrium and out)

Craniata (vertebrates) general characteristics

Nerve cord, pharyngeal slits and tail remain
Notochord disappears (replaced by vertebrae)

Main innovations of chordates

Formation of living endoskeleton (cranium + vertebrae)
Calcium phosphate skeleton

Why is the calcium phosphate skeleton important

Not heavy + grows with body

Two branches of craniata

Agnatha
Gnathostomatha

Agnatha

Jawless

Gnathostomatha

With jaws

2 types of agnatha

hagfish and lampreys

Lampreys

Cranium
Rudimentary vertebrae

Hagfish

Cranium
Without vertebrate

Gnathostomatha origin of jaws

Modification of first two gill arches

First arch

Became main part of jaws

Second arch

Became main support

Jaw shape and arrangement allowed

Adaptive radiation

Gnathostomatha include

Fish
Amphibians
Reptiles
Birds
Mammals

Two main types of fish

Chondrichtyes and osteichthyes

Chondrichtyes (Cartilaginous Fish)

Sharks and rays

Osteichthyes (bony fish)

Common fish

Five key characteristics of cartilaginous fish

Heteroceral tail
Placoid scales
Exposed gill slits
Large pectoral slits
Ventral mouth

Shark morphology

Sharks have jaws with rows of teeth that they renew regularly
Mouth opens to pharynx and to gill slits

Shark locomotion

Streamlined body for speed swimming + strong heterocercal tail and large pectoral fins

Sharks highly developed sensory organs

Great vision with enlarged view fields
Great olfactory system
Lateral line to detect vibrations