phylum: chordata

Phylum: Chordata

All chordates have (at some point)

A notochord A dorsal hollow nerve cord Gill slits Muscle blocks Bilateral symmetry Coelom Segmentation

Not all of these characteristics are apparent in adult organisms and may appear only in the embryonic or larval stages.

Chordates: Can be with or without a backbone

Invertebrate Chordates – Sea Squirts (tunicates), Lancelets

Vertebrate Chordates – Birds, fishes, mammals, amphibians, reptiles

1. Notochorda flexible, rodlike structurea flexible, rodlike structure

Extends the length of the body and is an anchor Extends the length of the body and is an anchor point for muscles – allows for powerful movement point for muscles – allows for powerful movement

In invertebrate chordates and the jawless vertebrates In invertebrate chordates and the jawless vertebrates (ex. Lamprey) the notochord is present throughout (ex. Lamprey) the notochord is present throughout life (no backbone)life (no backbone)

However, in the jawed vertebrates it is replaced by However, in the jawed vertebrates it is replaced by the vertebral column (the backbone)the vertebral column (the backbone)

2. Dorsal Hollow Nerve Cord (DHNC)

Develops from ectoderm that rolls into a hollow tube

The anterior end of nerve cord is enlarged in vertebrates into a brain

The posterior end of the nerve cord is the spinal cord.

3. Gill Slits

Gills slits are paired openings in the pharynx/behind the mouth

The gill slits are used as a filter feeding device in sea squirts and lancelets

Gills slits in fish develop into internal gills

Gills slits disappear in humans as they develop

Humans – embryonic gill slits

Lancelet

4. Muscle Blocks

Modified body segments of stacked muscle layers

Muscle blocks anchor to the notocord

Fish meat = muscle blocks

Muscle blocks develop into more developed muscle tissue in humans and other animals

Lancelet – V shaped muscle blocks

Fish muscle blocks

5. Bilateral Symmetry:a single plane divides body into two mirror images

6. Body Cavity: Coelom

The coelom is a cavity entirely surrounded by mesoderm.

A coelom provides a tube-within-a-tube arrangement which has many advantages: Allows visceral organs to grow independently of

the body wall

7. Segmentation

Divided into a series of parts

8. Tailan extension of the body past the

anal opening

The postanal tail allows some organisms to swim and its efficiency has been enhanced by the addition of fins.

The postanal tail is present only in vestigial form in humans (the coccyx) although tails as a whole are widespread among vertebrates.

Subphyla: Urochordata

Urochordates- example: tunicates or sea squirts

Invertebrate chordates p. 796 Fig. 29.9 Tunicates exhibit the dorsal hollow nerve cord,

notochord, gill slits and muscle block in the larval (immature) stage.

Sessile and colonize as adults—gill slits are the only chordate characteristic maintained as an adult.

Filter feeds

0147.jpg

Synoicum pulmonaria  a colonial sea squirt

Subphylum: Cephalochordata

Cephalochordata- example: lancelets p. 707 Fig. 29.10

Invertebrate chordatesExhibit notochord, dhnc, muscle block and

gill slits throughout their lifefilter feed

Lancelets

small (3-7 cm long) fishlike animals that inhabit sandy sediments of coastal waters.

They lack a distinct head and have no cranium.

There are 29 species, five of which occur in North American coastal waters.

Figure 23.09a

Subphylum: Vertebrata

Vertebrata-fish, amphibians, reptiles, birds and mammals

Exhibit notochord, dhnc, muscle blocks and gill slits at some point of development.

dorsal hollow nerve cord becomes the spinal cord notochord becomes the backbone (vertebral column) gill slits present in all embryos and maintained in fish and

some amphibians and reptiles at different stages of development.

muscle blocks and tail present embryonic in all vertebrates, present in the adult form in some vertebrates

Chordates have sophisticated equipment including . . .

a closed circulatory system with a multi-chambered heart

bilateral symmetry with lots of cephalization (and sophisticated sense organs)

an internal skeleton that grows with usan extraordinary immune systema digestive tract with lots of specialized

portions