• 1.2 Phylum Chordata

    Discussion corner
    1. Look up the meaning of the following words; backbone, notochord, exoskeleton and endoskeleton from reference materials provided.
    2. Write the meaning of the words in your notebook.
    3. Share your findings with classmates.
    4. Did you all get the meanings right? I have discovered that …. The term ‘chordata’ comes from theord chorda which means chord. Organisms in this phylum, at one time in their life have a chord-like structure called notochord. The facts We differ from other organisms because we have a backbone that enables us to stand upright. The main characteristics of organisms in phylum Chordata are:
    1. Presence of a chord like structure called notochord. The notochord supports the body in lower
    chordates while in higher chordates (vertebrates) it is present only during embronic stages. It is replaced by a vertebral column.
    2. Presence of a vertebral column which forms part of an internal skeleton. Vertebral column is a bony structure made up of vertebrae. It protects the spinal cord.
    3. Presence of a nervous system with a brain which is connected to a hollow nerve tube or a single tubular nerve cord. The nerve tube runs along the back and forms a brain anteriorly.
    4. Bilateral symmetry: this means that the body can be divided along one plane into two equal halves that are roughly mirror images of each other.

    Look at these pictures below. Can you state all the similarities and differences among the organisms.

    All the animals in the picture belong to phylum chordata. Based on this, what can you say about phylum chordata? Organisms in the phylum Chordata can further be subdivided into 5 different
    classes. These are:
    • Pisces (fishes)
    • Amphibia
    • Reptilia
    • Aves (birds)
    • Mammalia
    Class Pisces
     Latin word ‘Piscis’ which means fish. Therefore, the class pisces is made up of the fish family. The class consists of all type of fish such as:
    • Tilapia • Nile perch
    • Cod fish • Shark
    • Ray fish • Mud fish

    Activity 1.2: To examine external features of fish
    Requirements
    • Tilapia or any other type of fish (freshly killed)
    • Hand lenses
    • White tiles
    • Gloves
    • A pair of forceps
    Procedure
    1. Using the hand lens, observe the body surface of the fish and note the arrangement of the scales.
    2. Put on the glove on one hand and place the hand on the anterior part; slowly move your hand over the body surface of the fish towards the tail region. How do you feel?
    3. Using a pair of forceps, gently lift the flap-like structure (operculum) covering the gill chamber to expose the gills.
    4. Note the shape of the body of the fish.
    Study questions
    Discuss the following questions in your groups then present to the rest of the class.
    (a) State the observable external features which all fish possess.
    (b) Draw the arrangement of scales on fish.
    (c) Draw the structure of a gill.
    (d) What is the function of the gills bserved in the gill chamber?

    The facts
    Main characteristics of animals in class Pisces
    1. All fishes are aquatic. They live in places such as seas, lakes, oceans, rivers and dams.
    2. The skin of the fish is covered with scales which overlap backwards.
    3. Fish have gills which are used for gaseous exchange. The gills are located in a space called gill cavity on the side of the head. The number of gills in a fish ranges from 4 - 7 pairs.
    4. Fish have fins that aid in movement. The fins on the sides of the body are usually found in pairs, for example, the pelvic and pectoral fins. The dorsal, ventral and tail fins are usually unpaired.
    5. Fish are poikilothermic: Their body temperature is dependent on environmental temperature because they cannot regulate their own body temperature.
    6. Fish exhibit external fertilisation where eggs are first laid by the female then the male sheds sperms over them.
    7. Fish have a lateral line on their body for sensitivity.
    8. Fish have a single circulatory system with a two chambered heart.



    Note: Fish use gills for gaseous exchange except lung fish that lives in oxygen deficient swamps and use lungs for breathing.
    Adaptation of fish to aquatic environment How does fish survive in water?
    Research Activity
    1. Using reference materials such as textbooks and the internet, research on the adaptive features
    of a fish. Use the following questions as a guideline.
    a) What kind of body symmetry does fish have?
    b) Describe how the following structures enable fish to live in water:
    i) Body shape
    ii) Arrangement of scales
    iii) Fins
    iv) Gills
    v) Scales
    2. Compare your finding to the ones below.
    The facts
    The following features enable fish to survive in water.
    1. Gills Fish use gills to breathe under water. Most fish have to swim constantly. This enables water to pass through the gills to allow for gaseous exchange.
    2. Streamlined body The body shape of a fish is well suited to its particular habitat. Most fish have
    a streamlined body to allow water to easily pass over them, reducing friction (resistance) as they swim.
    3. Fins and tails
    Fins and tails allow fish to move through water. The tail propels the fish while fins guide their movement in water by controlling their direction and balance.
    4. Lateral lines
    The lateral line allows fish to detect vibrations in water, alerting them of predators.
    5. Huge number of eggs
    A single fish can lay more than a million eggs, which can all be fertilised. However, a lot of eggs are eaten by predators while others are washed away by water currents. A large number of eggs ensures that at least some will survive to maturity.
    Class Amphibia
    The word amphibia comes from the word ‘amphi’ which means ‘dual’ or ‘two’. This class of chordates can live both on land and in water. Most adult amphibians live on land. However, they go back to the
    water to breed. Examples are:

    Activity 1.3: To examine external features of amphibians
    Requirements
    • Preserved specimen of toads and frogs or freshly killed.
    • Photos and illustration of newts and salamanders. Procedure
    1. Examine the external features of the specimen provided. Note the following:
    (a) The nature of the skin.
    (b) Presence or absence of scales.
    (c) Number of legs.
    2. Draw a labelled diagram of a toad, a newt and a frog. Caution: Do not touch the warty skin of toads. It contains glands which produce poison. Study questions
    a) What is the difference between a toad and a frog?
    b) Do these amphibians have scales on their skins?
    c) How many legs do these amphibians have?
    d) Share your findings with the rest of the class.
    The facts
    Main characteristics of animals in class Amphibia
    1. They have mucus glands under the skin to keep it moist.
    2. The skin has no scales unlike that of fish and reptiles. (Reptiles will be,discussed later in this unit).

    3. Adult amphibians use the lungs, moist skin and mouth cavity for gaseous exchange. However, their
    young ones use external gills for gaseous exchange while in water.
    4. The adult female amphibians always lay their eggs in water.
    5. They exhibit external fertilisation.
    6. They have two pairs of limbs.
    Class Reptilia
    The term ‘Reptilia’ comes from a latin word, ‘Reptilis’ which means ‘crawl’. The animals in this class move by creeping or crawling. Unlike amphibians, reptiles do not breed in water because they lay
    eggs with leathery shells; hence cannot dry out. Examples of reptilia are; snakes, turtles, tortoises, crocodiles and lizards


    Activity 1.4: To examine external features of reptiles
    Requirements
    • Live specimens of non-poisonous reptiles such as lizards
    • Preserved specimens
    • Photos and pictures
    • Films and videos on lives of reptiles
    Procedure
    1. Observe the specimens, photos and illustrations provided carefully.
    2. Do the following:
    (a) Note the nature of the skin.
    (b) Note the presence and number of limbs.
    (c) Count the number of limbs and the terminating digits.
    Caution: Do not attempt to catch live animals like snakes or even go close to them because they are
    poisonous and dangerous. Study questions
    a) How are the scales attached onto the skin?
    b) Is the skin of reptiles moist or is it dry?
    c) Compare the scales of reptiles to those of fish.
    d) Which reptile does not have legs?
    e) How many legs do the other reptiles have?
    f) What is the habitat of each of the reptiles studied?

    The facts
    Main characteristics of animals in Class Reptilia
    1. They have a dry scaly skin. Some like the tortoise have scales which have hardened to form a shell.
    2. They are mostly terrestrial with a few being partially aquatic.
    3. They undergo internal fertilisation, where the male introduces sperms into the female body. The eggs laid thereafter are covered with a shell.

    4. Most of them have two pairs of legs except the snake.


    Class Aves (birds)
    The term ‘aves’ comes from a Latin word ‘Avis’ which means bird. Animals in this class consist of birds such as the humming bird, ostrich, fowl, sparrow, hawk, eagle, sea gull, parrot, crow and ibis.
    Look at the following pictures. Have you ever see them?
    Activity 1.5: To examine external features of birds
    Requirements
    • Photos and illustrations of different kinds of birds.
    • Live specimen of caged or domestic birds.
    Procedure
    1. Examine the birds, photographs and illustrations carefully.
    2. Note the following:
    (a) The nature of the skin
    covering on their body.
    (b) The skin on their legs.
    (c) Number of limbs.
    (d) Adaptation of the limbs to their function.
    (e) The nature of the feathers.
    3. Draw and label different parts of the bird.


    Main characteristics of Class Aves
    1. Their bodies are covered with feathers.
    2. Their legs are covered with scales.
    3. Their front limbs are modified to form wings. The hind legs are used for walking, running, swimming mamong other uses.
    4. They have hollow bones that make them light for flight.
    5. They have toothless jaws covered by a horny beak or bill.
    6. They lay eggs with a hard shell madeof calcium.
    7. They carry out internal fertilisation.


    Adaptations of birds to their environment
    Discussion corner
    1. Using text books and the internet find out the adaptive features of birds.
    2. Answer these questions:
    a) Why do birds have wings?
    b) What is the importance of birds having a streamedlined body?
    c) Why do birds have hollow bones?
    d) Why do birds have beaks?



    1. The forelimbs of birds are modified to form wings for flight. The sternum of pectoral girdle is expanded for attachment of flight muscles.
    2. Flight birds are light in weight. Their bones are air-filled and therefore have low density to enable ease of flight.
    3. Birds lay eggs with hard calcareous shells to avoid drying out.
    4. The beaks of birds are modified for different modes of feeding, for example:
    • Seed eaters – like sparrows have short thick conical bills for cracking seeds.
    • Flesh eating birds – like hawks have sharp curved beaks for tearing meat.
    • Nectar eating birds – like humming birds have long slender beaks to probe the flowers.
    • Insect eaters – like bee-eater have thin pointed beaks.
    • Filter feeders – have serrated beaks to filter food from muddy water. An example is the duck and flamingoes.
    • Water plant eaters – like ducks have flat beaks to strain small plants and animals  the water.

    Activity 1.6: To Identify the mode of feeding of the birds whose beaks are shown below.
    Use a table like the one given below.
    Table 1.1: Birds and their mode of feeding


    5. Birds have different types of feet to  them to their different environments. These include:
    • Feet for grasping – like those of a kingfisher. They are large and curved to grasp a prey tightly.

    • Feet for scratching – like those of chickens. They have  nail-like toes to scratch the soil for food.
    • Swimming birds – like ducks have webbed feet used like paddles.
    • Perching feet – like that of a robin. They have long back toes to grab and perch tightly on a tree branch or bark.
    • Feet for running – like those of ostrich. They have three toes to enable stability when running.

    Activity 1.7: Identify the adaption of the bird's feet shown below. Use a table like the one given below.
    Table 1.2: Birds and their feet adaptation

    2. Draw the expected type of feet to match the type of beak in birds.
    Use a table like the one given below.
    Table 1.3: Matching birds beaks to feet

    Class Mammalia
    The term Mammalia is derived from the Latin word ‘mammalis’ which means ‘mammal’ or ‘mamma’ which means milk secreting organ of female mammals. Most mammals are terrestrial except a few like dolphins and whales which are aquatic.
    • Name some organisms in this class.

    Activity 1.8: To examine theexternal features of mammals
    Requirements
    • Live specimen of animals in class Mammalia in the school compound such as rabbits or rats.
    • Photos of aquatic mammals.
    • Illustrations and videos of other members of class Mammalia.
    Procedure
    1. Examine the animals of class Mammalia found in your school compound or in the school
    surroundings.
    2. Recall a goat or a cow in your home or at your neighbour.
    3. Note the following:
    • Presence of mammary glands.
    • Presence of hair or fur on the skin.
    • The nature of the ears.
    4. Locate a mammal with young one(s). For instance a rabbit with its litter.
    • What is the behaviour of the mother towards its young ones?Study questions
     (a) What is the importance of mammary glands in a mammal?
    (b) What is the covering on the skin of mammals?
    (c) Describe the ears of mammals.


    Main characteristics of animals in Class Mammalia
    1. They have mammary glands. They suckle and take care of their young ones.
    2. Their bodies are covered with fur, hair or wool.
    3. They give birth to young ones except the duck-billed platypus and spiny ant-eater which lay eggs.
    4. They have external ears. These arethe only class of chordates that have the external ears.
    5. They exhibit internal fertilisation.
    6. They are Homeothermic. Their body temperatures do not depend on the environment. It  ismaintained constantly.
    7. They have differentiated teeth (i.e incisors, canines, pre-molars and molars) each with different function. They are therefore referred to as heterodonts. Others with uniform teeth differing only in size are homodonts.

     



    Unit 1: Classification of Kingdom Animalia1.3 Phylum Arthropoda