Biology 11Higher Chordata:

Subphylum Vertebrata:The Fishes

Higher Chordata Objectives: Vertebrata

• Describe the 3 Classes and an example animal

• Anatomy of a ray finned fish

Subphylum 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 adult3. Pronounced cephalization4. A closed circulatory system

Characteristics of All Fish

• 1. breathe using gills

• 2. have 2 chambered hearts (and closed circulatory system

• 3. reproduce sexually

• 4. highly developed sensory system

Characteristics of All Fish• 1. breathe using gills

• as a fish takes water in through its mouth, water passes over the gills & then out through slits at the side of the fish

• 2. have 2 chambered hearts• One chamber receives oxygen-poor blood from the body tissues• The other chamber pumps blood directly to the capillaries of the

gills, where oxygen is picked up & carbon dioxide released

• 3. reproduce sexually • Fertilization & development is external in MOST fishes• Eggs & sperm can be released directly into the water, or

deposited in more protected areas

• 4. highly developed sensory systems• Have eyes that allow them to see objects & contrasts between light & dark in the water, but the amount of vision varies among

fishes

Class Agnatha

Jawless fishes• Much more dominant in the early oceans where

they were mud suckers or filter feeders – no articulating jaws

• Represented today by Lamprey and Hagfish

Class Agnatha

• Evolved gills to improve oxygen uptake and thus increased activity levels

• No paired appendages• have smooth, scaleless skin & long cylindrical

body • have cartilaginous skeleton • no vertebral column • only vertebrates to retain notochord through all

stages of their life

Lampreys - most are parasites

hagfish

Class Chondrichthyes

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• have a lateral line system that enables them to

sense objects and changes in their environment– is a line of fluid-filled canals running along the sides of a

fish that enable it to detect movement and vibrations in the water

• Can sense electric currents in water• Are almost all predators• Developed internal fertilization and carry eggs

internally (no nutritional connection) as young must swim when born

• They are: sharks, skates, and rays

Sharks

• have tough, leathery skin that is covered with PLACOID SCALES

• mouth is lined with 6-20 rows of sharp teeth which continuously form and move forward to replace lost or worn teeth

• swim continuously – they are denser than water – suffocate if water not moving over gills

• large, oily liver that can make up nearly 20% of its total body weight – liver oil is lighter than water and gives sharks buoyancy

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

Class Osteichthyes (bony fishes)• There are two main groups of

fish seen today:1. Ray finned fish: • true fish with ray finned

appendages • Evolved in fresh water then

moved back to the oceans• Most common fish today

(salmon, trout etc)

Class Osteichthyes

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

Class Osteichthyes (bony fishes)

• Have a calcified skeleton (bones!!)• Well developed system for motility (ray finned fish)– use their paired pectoral and pelvic fins to steer,

brake, move up and down, and even swim backwards

– air bladder – a thin-walled sac in the abdominal cavity filled with gas dissolved

gases in the blood diffuse into & out of the swim bladder• as the bladder fills up, the fish rises and when it deflates, the

fish sinks

• Have an operculum (covering over gills)

• skin is covered with thin, round scales, called CYCLOID SCALES, which overlap like shingles (can determine age by counting rings of scales

• mucus covers scales giving the fish a slimy surface

• Unlike sharks, can pump water through their gills even when motionless

Class Osteichthyes

1. Circulatory System

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

Class Osteichthyes

2. Response/nervous system•vertebrate brain and well developed senses•Eyes that detect light/dark•have two pairs of nostrils as well as chemical receptors scattered over their head and body. – Smell usually gives fish their first clues about

food, mates, and enemies•Lateral line that enables them to sense objects and changes in their environment (vibrations)

Class Osteichthyes

3. Reproduction• Have external fertilization and little if any post

natal care• Young are born able to swim and feed and must

fend for themselves4. Excretory System• Have a dorsal kidney that excretes mainly

ammonia as nitrogen waste

• End

• http://www.youtube.com/watch?v=d7WtduFycDY

• Living planet the open ocean