Most animals move from place to place in search of food.

Major phyla are:

  1. Platyhelminthes (Tapeworm).
  2. Nematoda (Ascaris).
  3. Annelida (Earthworm).
  4. Mollusca (Snails).
  5. Arthropoda
  6. Chordata



Phylum Arthropoda

Distinguishing Characteristics of Phylum Arthropoda

  1. They have jointed appendages, which are specialised for various functions.
  2. Their body is covered by a hardened exoskeleton made of chitin.
  3. It is shed at intervals to allow for growth.
  4. They have jointed body parts.
  5. Most are divided into head, thorax and abdomen.
  6. Some have two body parts,



General Characteristics of  phylum Arthropoda

  • Body is segmented.
  • They have bilateral symmetry.
  • Gaseous exchange is through tracheal system, book lungs or gills which opens to the outside through spiracles.
  • Aquatic forms use gills.
  • Reproduction is mainly sexual.
  • They have an open circulatory system.


Phylum Arthropoda divided into five classes;

  1. Crustacea,
  2. Arachnida,
  3. Chilopoda,
  4. Diplopoda
  5. Insecta

This division is based on:

  1. The number of limbs.
  2. Presence and number of antennae.
  3. Number of body parts.



Class Crustacea

  • Most of them are aquatic, a few are terrestrial found in moist places e.g., woodlouse.

Distinguishing Characteristics of Class Crustacea

  1. Two body parts head and thorax are fused to form cephalothorax and an abdomen .
  2. They have two pairs of antennae; one is small and branched, the other is long.
  3. They have five or more parts of limbs.
  4. Some of these are modified for other functions e.g., locomotion, feeding and defence.
  5. Exoskeleton hardened with deposits of calcium carbonate i.e. carapace.

Other Characteristics of Class Crustacea

  1. Mouthparts include a pair of mandibles and two pairs of maxillae.
  2. Gaseous exchange is through gills.
  3. They have a pair of compound eyes.
  4. Most crustaceans are free-living but a few are parasitic e.g., barnacles.
  5. Examples are cray-fish and crab.



Class Arachnida

Members are carnivorous and paralyse prey using poison produced from poison claws.

Distinguishing Characteristics of Class Arachnida

  1. The body has two parts: cephalothorax and abdomen.
  2. Cephalothorax is head fused to thorax.
  3. A pair of chelicerae, on ventral side of cephalothorax.
  4. They have four pairs of walking legs.
  5. They have no antennae.
  6. Instead they have a pair of short pedipalps which are sensitive to touch.
  7. Most arachnids use book lungs for gaseous exchange.
  8. Other characteristics include simple eyes.
  9. Examples include garden spider, ticks, scorpions.


Class Chilopoda e.g. Centipede

Distinguishing Characteristics of Class Chilopoda

  1. The body has 2 body parts, a head and trunk.
  2. The body is elongate, and has 15 or more segments.
  3. Has a pair of legs on each segment.
  4. The body is dorso-ventrally flattened.

Other characteristics include:

  1. Head has a pair of antennae.
  2. Gaseous exchange through tracheal system.
  3. Are carnivorous.



Class Diplopoda e.g. Millipede

Distinguishing Characteristics of Class Diplopoda

  • Has two parts: head, short thorax and a trunk.
  • Body elongate with 9-100 segments.
  • Has two pairs of legs on each segment.
  • They have a cylindrical body.
  • Gaseous exchange is by tracheal system.

Other characteristics:

  • Head has a pair of antennae.
  • Are herbivorous.


Class Insecta

Distinguishing Characteristics of Class Insecta

  • Body is divided into three body parts head, thorax and abdomen.
  • They have three pairs of legs ..
  • Most insects have a pair or two of wings.

Other characteristics include:

  • A pair of antennae.
  • They breathe through spiracles, and gaseous exchange is through tracheal system.


The class is divided into several orders based on:

  1. Mouth parts- – type e.g. biting or piercing.
  2. Position of mouthparts – ventral or anterior.
  3. Wings – presence or absence; number of wing types, structure, texture.
  4. Size of legs.


Order Orthoptera

  1. Have biting and chewing mouthparts.
  2. Hind legs longer than other legs e.g. fore wings, leathery and longer than hind legs. e.g. locusts and grasshoppers .
  3. Swarming – locusts are a menace to farmers and the environment as they destroy crops and vegetation.


Order Diptera

  • True flies e.g. houseflies, and mosquitoes have sucking and piercing mouthparts, 1 pair of wings.
  • The second pair is vestigial- acts as balancer.
  • Mouthparts are ventral.
  • These are disease vectors e.g., female anopheles mosquito transmits malaria.


Order Lepidoptera

  • Butterflies and moths have sucking mouthparts,
  • Two pairs of wings covered by scales.
  • This group is important to farmers in pollination.


Order Hymenoptera

  1. Bees, wasps, ants.
  2. They have sucking mouthparts, two pairs of wings which are membranous.
  3. Some are non-winged e.g. some ants.
  4. Bees are important in pollination i.e. in production of honey.


Order Isoptera – Termites

  1. They have biting mouthparts which are anterior.
  2. Most are wingless,
  3. Those with wings they are membranous and of the same size.
  4. They are important in nutrient cycling as they feed on cellulose.


Order Coleoptera – Beetles

  1. Have biting mouthparts,
  2. Two pairs of wings,
  3. Fore wing hardened enclosing membranous wings.
  4. Destruction of stored grains and legumes (pulses)


Phylum Chordata

  1. This name is derived from the term notochord.
  2. This is a long flexible rod-like structure.
  3. The more familiar chordates are known as vertebrates.
  4. In vertebrates the notochord exists only in embryonic stages of development which in later stages is replaced by a vertebral column.


See also




Scheme of work


Leave a Comment

Your email address will not be published. Required fields are marked *

Get Fully Funded Scholarships

Free Visa, Free Scholarship Abroad

           Click Here to Apply