Chordates: Phylum Chordata

An Introduction to Vertebrate Animals

IntroductionChordates (vertebrates) are the group of

animals most familiar to usEx: mammals, birds, amphibians, reptiles, fishName comes from: Notochord “Back” “Cord”

Def: a skeletal rod made of body of cells enclosed by a fibrous covering, which extends, in most cases the length of the body

Primary purpose/function: to support and stiffen the body, provide muscle support

In most vertebrates the notochord is displaced by vertebrae

Introduction

Five distinct/unique characteristics** to chordates:1) Dorsal, tubular nerve cord (anterior end becomes enlarged to

form brain)2) Notochord 3) Pharyngeal slits /pouches (will become middle ear cavity,

tonsils, parathyroid glands, etc.)4) Endostyle (becomes thyroid gland) for filter feeders 5) Post-anal tail for propulsion (vestigial structure in humans;

coccyx)

** Some of these characteristics appear ONLY in the embryonic (pre-birth) stages of vertebrates!!!

Introduction

Chordates have many characteristics that are similar to some invertebrate animals:

1. Bilateral symmetry (like mollusks, arthropods)Anterior to posterior axis , right/left halves

2. Coelom well developed (Tube-within-a-tube arrangement )

3. Metamerism (segmentation) restricted to outer body wall, head and tail and not into coelom

4. Cephalization (concentrated head region)

Introduction

Chordates have many characteristics that are similar to some invertebrate animals:5. Endoskeleton (some mollusks, arthropods)6. Paired appendages (arthropods)7. Sensory organs are highly developed

(mollusks, some arthropods)8. Three germs layers (ectoderm, mesoderm,

endoderm)9. Complete digestive system

DiversityBelong to Phylum ChordataEnormous variationLive in all ecosystems on earth

Most adaptable phylum on earthLARGE fossil record

According to fossil record, chordates are ~500 million years old

Approximately 60,000 different species

CharacteristicsEndoskeleton:

Grows as animal growsSeries of vertebrae surrounding a spinal cord Skull is attached to anterior end of backbone

(head-region)Functions:

Protection, muscle attachment, organ attachment

Characteristics

Circulation:Closed system Contain arteries, vessels, veins, ventral heartAllows for rapid circulation of bloodMost have separation of oxygenated and

deoxygenated bloodCan regulate body temperature (one of two ways)

1) Endotherms – control with internal body processes (mammals, birds)

2) Exotherms – control by outside environment (fish, amphibians, reptiles)

CharacteristicsEndocrine system:All chordates have a thyroid glandFunction: to produce hormones

Nervous system:Cephalization is presentConcentrated in anterior regionVERY highly developedAllows for much, higher-order processes Sensory receptors highly developed (eye, nerve endings,

brain processes, etc)

Classification: 3 SubphylaThree subphyla:

1) UrochordataExample: sea squirt

2) CephalochordataExamples: lanceletes

3) VertebrataExamples: birds, mammals, reptiles, amphibians

ClassificationThree subphyla:

1) UrochordataKnown as tunicatesExamples: sea squirts2000 speciesFound in all seas (shoreline to great depths) Most are sessile (permanent) adults, some are free living Name tunicate comes from “tunic”

This is a tough surrounding that protects animal May be solitary or live in colonies Hermaphrodites (contain both sexes)

ClassificationThree subphyla:

2) CephalochordataExamples: lanceletesOnly 25 speciesFound in marine environments

Sandy bottoms of coastal regionsVERY small (5-7 cm in length)Free living, swimmersSeparate sexesConsidered the evolutionary beginning to all other

chordates

ClassificationThree subphyla:

3) VertebrataExamples: mammals, birds, fish, amphibians, reptilesLargest and most diverse chordate subphylum~57,000 speciesFound in all ecosystems, environmentsWIDE range of sizesGrouped together because of the skull region (bony or

cartilaginous braincase) Tripartite brain (fore, mid and hindbrain)

Can possess both endoskeleton AND exoskeleton