Biology 11Phylum Chordata:

Subphylum Vertebrata:The Fishys

We are going to spend the next few classes talking about the Subphylum Vertebrata (AKA: the higher chordates!)

Higher ChordatesPhylum Chordata is typically divided into four subphyla:

Describe the 3 Classes and an example animal

Anatomy of the Perch

Higher Chordata Objectives: Vertebrata

Characteristics:

1. Endoskeleton of bone or cartilage which surround the dorsal nerve cord (a backbone or vertebral column)

2. Notochord absent or reduced in adult

3. Pronounced cephalization

4. A closed circulatory system

Subphylum Vertebrata

Jawless fishes

Much more dominant in the early oceans where they were mud suckers or filter feeders – no articulating jaws

Evolved gills to improve oxygen uptake and thus increased activity levels

No paired appendages

Represented today by Lamprey and Hagfish

Class Agnatha

https://www.discovery.com/tv-shows/discovery-presents/videos/hag-fish-slime

Cartilagenous Fishes

Skeleton is made of cartilage not bone (secondarily evolved)

Evolved articulating jaws by modification of anterior two pairs of gill slits

Have no operculum or air bladder

Very streamlined body with paired fins for steering

Class Chondrichthyes

Have well developed senses, especially smell

Are almost all predators

Developed internal fertilization and carry eggs internally (no nutritional connection) as young must swim when born

Much more dominant in early oceans

They are: sharks, skates, and rays

Class Chondrichthyes

Hammerhead Shark

Tiger Shark

Rays:- Kite shaped- Thin barbed tails- Spines on tail- No thorns on tail

and back- Larger- Give birth to live young

Skates:- Rounded shape- Thicker heavier tails- No spines on tail- Thorns on tail and back- Elongated nose- Smaller- Lay eggs

The Bony Fishes

Have a calcified skeleton - are dominant water vertebrate

Have an operculum and air bladder (formed as a pocket off the pharynx)

Developed the structure that evolution would select for in moving the vertebrates to land

Class Osteichthyes

1. Circulatory System

Have a two chambered heart that pumps blood to the gills then the rest of the body

2. Nervous system

Have the basic organization of a vertebrate brain and well developed senses

Behaviours begin

Class Osteichthyes

3. Reproduction

Have external fertilization and development with little if any post natal care

Young are born able to swim and feed and must fend for themselves

4. Excretory System

Have a dorsal kidney that excretes mainly ammonia as nitrogen waste

Class Osteichthyes

Class Osteichthyes

There are two main groups of fish seen today:

1. Teleosts:

true fish with ray finned appendages

Evolved in fresh water then moved back to the oceans

Most common fish today (salmon, trout etc)

Pregnant Males?

http://channel.nationalgeographic.com/wild/videos/pregnant-males/

2. Lung fish and Lobe-finned fish

These two fish evolved in fresh water at a time when periodic and severe droughts occurred

Lung fish seen today in Africa and South America

Use their crude lungs to gulp air to assist gills (usually live in stagnant water)

Class Osteichthyes

Lobe-finned fish were mostly bottom dwellers and used their more sturdy fins to grope along the bottom of the swamps and to occasionally move about the muddy shores

Both of these fish are well represented in the fossil record

Class Osteichthyes

Vertebrates faced many problems moving onto land

Problems:

1. Gas exchange (moist membrane problem)

2. Movement: loss of buoyancy

3. Obtaining food - must adapt to new food especially tough plants

Evolution to Land

4. Dessication

5. Reproduction: with motile sperm

6. Development: all animal embryos develop in water

7. Senses: land is much more transparent than water - can be seen easier - much more to detect and react to

8. Adaptation: to rapid, severe climate changes

Evolution to Land

On to Land!

The bony fish evolved from the cartilagenousfishes, probably in fresh water

During the Devonian, the land became much hotter and drier

Water habitats both shrank and became stagnant

Evolution to Land

Shallow pools of water would dry up most quickly - problem for fish

Competition for food and space also intensified as the habitat shrunk

If your pond is drying out, to survive you need to get to another pool of water

Nature would select for any structure that would aid short term movement on land

Evolution to Land

Fleshy, sturdy fins would allow the fish to “steer” a course between water holes using the muscular tail for propulsion

This is very energetically costly: crude lungs were already developing as the stagnant water had too little oxygen (which evolved into air bladders in water fish)

Nature would select for better lungs

Evolution to Land

One advantage they would discover while in transit was unlimited food (no other major animals on land)

This would encourage them to stay longer on land

The end result would be a lobe finned, lung fish capable of limited movement on land

Evolution to Land

A Coelocanth, a lobe-finned fish!