Zoology Lecture 15 + 18 (BIO-2040)

Unique Characteristics of Chordates

1. Dorsal nerve cord

2. notocord

3. pharyngeal pouches/slits

4. post-anal tail

Dorsal Hollow Nerve Cord

• Other phyla have solid nerve cords

• central nervous system (brain and spine)

Notochord

• flexible, dorsal structure rod

• axis for muscle attachment, locates below nerve cord

• it persists in early chordates

• replaced by bones in vertebrates

Pharyngeal slits

similar to that of hemichordates

• originally for filter feeding, now adapted for feeding/respiration

Endostyle

A gland intimately associated with paryngeal slits, it produces mucus to trap food particles

Muscular post-anal tail

• usually related to segmented musculature

• primarly for propulsion

• works with notochord/vertebrates

• best developed in fish at larval or adult stages

Early Chordates

1. Cephalochordata

2. Urochordata

Later Chordates

Craniata

Cephalochordata

• about 23 species

• have all 4 chordate characteristics

• 5-15cm in length

Cephalochordata Locomotion

• use notochord and segemented muscles

Cephalochordata Feeding

• mouth pulls in water, goes through pharyngeal slits, food trapped by mucus, water goes into the atrium then out

Urochordata

• tunicates or sea squirts, about 3,000 species

• name from “tunic”

• look like barrets and have prominent brachial basket

• most are solitary

Urochordata Larva

have all 4 characteristics

Urochordata Adult

• gill slits remain

• notochord and tail disappear

• nerve cord becomes reduced

Urochordata feeding

Water circulation

• Incurrent Siphon → Pharynx → atrium and out

Craniata

• vertebrate (mostly)

• notochord replaced by spine

Craniata Innovation

• formation of living endo-skeleton

• not heavy, made from calcium phosphate

Craniata unique thing

They are made from calcium phosphate

Craniata radiation

1. Agnatha → no jaw

2. Gnathostomatha → with jaws

lamprey

• has cranium but only rudimentary vertebrate

• marine and freshwater (most parasitic)

Hagfish

• has cranium no vertebrate

• all marine

• slime eel

Gnathostomatha origin of jaw

from modification of first gill arch

→ first arch become main jaw

→ second arch became main support

→ first gill slit is reduced

Have cranium and well formed vertebrate

Gnathostomatha include

• fish

• amphibians

• reptiles

• birds

• mammals

Fish Classes

1. chondrichtyes (shark and ray)

2. Osteichthyes (bony fish)

Chondrichtyes

• about 850 species

• skeleton made of cartilage bones

• includes shark, ray and skates

Chondrichtyes key characteristics

• heterocercal tail

• placoid scales

• exposed gill slits

• large pectoral fins

• ventral mouth

Chondrichtyes general morphology

• sharks have jaws with rows of teeth they regrow frequently

• mouth opens to pharynx and gill slits

Chondrichtyes locomotion

• streamlined body for speed swimming 

• strong heterocercal tail and large pectoral fins

Chondrichtyes sensory organs

• great vision with enlarged view feilds

• olfactory system able to detect 1 part/ 10 billion

• lateral line to detect vibrations

Class Mammalia

hairy vertebrates with mammalia glands

subclasses of Mammalia

• monotremes

• theria

infraclasses of theria

• marsupials

• eutherian

Prototherians

monotremes

• very low diversity

• lay eggs

• platypus and echidna

• no nipples

• have a pouch for newborns and large cloaca

Metatherians

marsupials

• give birth to underdeveloped kids

• have a pouch

• kangaroos and tasmanium devil

• short gestation and long lactation

viviparous

give birth

oviparous

lay eggs

Eutherians

placentals

• over 90% of animals

• all babies have hair

• viviparous and have placenta

• short lactation and long gestation

four advanced social behaviours of eutherians

1. vocal communication

2. development of heirachys

3. friendship and sexual behaviour

4. high learning ability