CHARACTERISTICS OF VERTEBRATES

Bees are important in pollination i.e. in production of honey Members of the phylum have a notochord in early stages of development. They have visceral clefts – which are slits perforating the body wall at the pharynx.

In fish these slits become gills while in higher chordates these slits are only present in embryo. They have a dorsal, hollow nerve cord. It develops into a brain at the anterior and spinal cord at the posterior end.

The spinal cord is enclosed within the vertebral column. They have segmented muscle blocks known as myotomes on either side of the body. They possess a post-anal tail although rudimentary in some.

They have a closed circulatory system. The heart is ventrally located. They possess an internal skeleton.

The main classes of phylum chordata are;

1. Pisces,
2. Amphibia,
3. Reptilia,
4. Aves

Class Pisces

1. These are the fishes.
2. Some fish have a skeleton made of cartilage e.g. the shark.
3. Others like Tilapia have a bony skeleton.

Distinguishing Characteristics

1. They are aquatic.
2. Movement is by means of fins.
3. They have a streamlined body.
4. They have a lateral line for sensitivity.
5. Their heart has two chambers, the auricle and ventricle – simple circulatory system.

Other Characteristics

1. Their body temperature changes according to the temperature of the environment.
2. They are ectothermic (poikilothermic).
3. Body covered with scales.
4. They have gills for gaseous exchange.
5. Exhibit external fertilisation.

Class Amphibia

1. Larval forms are aquatic while adults are terrestrial.
2. Adults return to water for breeding e.g. frogs, toads, newts, salamanders.

Distinguishing Characteristics

1. Skin is soft and without scales.
2. They have four well developed limbs.
3. The hind limbs are longer and more muscular than forelimbs.
4. The limb can be used for walking, jumping and swimming
5. Gaseous exchange is through the skin, gills and lungs
6. Middle ear is present.

Other Characteristics

1. They have a three-chambered heart with two atria and one ventricle.
2. Fertilisation is external.
3. They are ectothermic (poikilotherms).

Class Reptilia

Examples are snakes, crocodiles, lizards, chameleons, tortoises and turtles. Distinguishing Characteristics

The skin is dry and is covered by horny scales. Fertilisation is internal.

Some species eggs contain a lot of yolk and have either leathery or calcareous shells.

They have a double circulatory system. The heart has three chambers – two atria and a partly divided ventricle. However crocodiles have a four chamber heart.

Other Characteristics

1. They are ectothermic (poikilothermic).
2. Have 2 pairs of limbs.
3. They use lungs for gaseous exchange.

Class Aves

These are birds. They are terrestrial and arboreal and others are aquatic e.g. flamingo, goose, ostrich, penguin, hawk, dove.

Distinguishing Characteristics

1. Body is covered by feathers and legs with horny scales.
2. They have two pairs of limbs.
3. Fore limbs modified to form wings for flight.
4. Hind limbs are for walking or swimming.
5. The mouth is a protruding beak.
6. They have hollow bones.
7. They have double circulation with a four-chambered heart (2 atria, 2 ventricles).
8. They have lungs for gaseous exchange.
9. Lungs are connected to air sacs in bones.
10. Fertilisation is internal.
11. They lay eggs with calcareous brittle shell.
12. They have constant body temperatures hence are homoiotherms (endothermic).

Class Mammalia

They are arboreal e.g. tree-squirrels, Others terrestrial e.g. humans Others are aquatic e.g. dolphins and whales.

Distinguishing Characteristics

1. They have mammary glands hence name of the class.
2. Body is covered with fur or hair.
3. Their teeth are differentiated into four types (heterodont dentition).
4. They have external ear-pinna.
5. Most have sweat glands.
6. They have a diaphragm that separates the body cavity into thoracic and abdominal.

Other Characteristics

1. Internal fertilisation – most give birth.
2. They have a double circulatory system with a four-chambered heart.
3. They are endothermic (homoiotherms) .

Eg Duck-billed Platypus (egg-laying mammal)

Eg.Kangaroo (pouched mammal)

The young are born immature and are nourished in a pouch with milk from mammary glands.

Placental Mammals

1. They give birth to fully developed young ones which are fed on milk from mammary glands.
2. Some are aquatic. e.g. dolphins, whale,
3. Others are flying e.g. bat;
4. Most are terrestrial e.g. rabbits, elephants, buffalo, giraffe, antelope, cow, human being.

Placental mammals are divided into various orders

1. Rodentia: e.g. rats, mice – have one pair 9f upper incisors.
2. Insectivora: e.g. mole-they are like rodents:
3. Carnivora: e.g. dog; lion – flesh eaters, they have long pointed canines.
4. Cetacea: e.g. whales and dolphins ¬Aquatic mammals. Forelimbs are flippers.
5. Chiroptera: e.g. bats – Forelimbs form wings.
6. Artiodactyla: e.g. antelopes, cattle – they are even toed with split hooves.
7. Perissodactyla: e.g. horse, donkey – they are odd toed with hooves.
8. Proboscidea: e.g. elephant – upper lip and nose elongated to form trunk.
9. Lagomorpha: e.g. rabbit, hare – mammals with upper and lower incisors. Have larger hind legs than forelegs.
10. Primata: e.g. gorilla, orang utang, chimpanzee, monkeys – some are arboreal, with hand and foot for grasping.
11. Human – Homo sapiens – upright gait, opposable thumb hence use of tools.

Construction and Use of Dichotomous Keys

1. Biological keys are sets of statements that act as clues leading to the identification of an organism.
2. By following the keys we can be able to place an organism in its group.
3. The most common key is the dichotomous key.
4. This is a biological tool for identification of unknown organisms.
5. The word dichotomous means branching into two.
6. A single characteristic is considered at a time.
7. Two contrasting statements are put forward to describe the characteristics in such a way as to separate the organisms.
8. This continues until all the organisms have been identified.

Rules Used to Construct a Dichotomous Key

Use morphological characteristics as far as possible e.g. type of leaf – simple or compound.

Select a single characteristic at a time and identify it by number.

1. Type of leaf. .

Use identical forms of words for two contrasting statements e.g.:

1. a) Flowers scented.
2. b) Flowers not scented.

Start with a major characteristic that divide the organisms into two large groups then proceed to lesser variations that would separate the organisms further into smaller groups.

Use positive statements especially the first one.

Avoid generalizations e.g. short plants. Be specific in your description e.g.:

1. a) Plants above 1m tall.
2. b) Plants below 1m tall.