Most animals move from place to place in search of food.
Major phyla are:
- Platyhelminthes (Tapeworm).
- Nematoda (Ascaris).
- Annelida (Earthworm).
- Mollusca (Snails).
- Arthropoda
- Chordata
Phylum Arthropoda
Distinguishing Characteristics of Phylum Arthropoda
- They have jointed appendages, which are specialised for various functions.
- Their body is covered by a hardened exoskeleton made of chitin.
- It is shed at intervals to allow for growth.
- They have jointed body parts.
- Most are divided into head, thorax and abdomen.
- 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;
- Crustacea,
- Arachnida,
- Chilopoda,
- Diplopoda
- Insecta
This division is based on:
- The number of limbs.
- Presence and number of antennae.
- 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
- Two body parts head and thorax are fused to form cephalothorax and an abdomen .
- They have two pairs of antennae; one is small and branched, the other is long.
- They have five or more parts of limbs.
- Some of these are modified for other functions e.g., locomotion, feeding and defence.
- Exoskeleton hardened with deposits of calcium carbonate i.e. carapace.
Other Characteristics of Class Crustacea
- Mouthparts include a pair of mandibles and two pairs of maxillae.
- Gaseous exchange is through gills.
- They have a pair of compound eyes.
- Most crustaceans are free-living but a few are parasitic e.g., barnacles.
- 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
- The body has two parts: cephalothorax and abdomen.
- Cephalothorax is head fused to thorax.
- A pair of chelicerae, on ventral side of cephalothorax.
- They have four pairs of walking legs.
- They have no antennae.
- Instead they have a pair of short pedipalps which are sensitive to touch.
- Most arachnids use book lungs for gaseous exchange.
- Other characteristics include simple eyes.
- Examples include garden spider, ticks, scorpions.
Class Chilopoda e.g. Centipede
Distinguishing Characteristics of Class Chilopoda
- The body has 2 body parts, a head and trunk.
- The body is elongate, and has 15 or more segments.
- Has a pair of legs on each segment.
- The body is dorso-ventrally flattened.
Other characteristics include:
- Head has a pair of antennae.
- Gaseous exchange through tracheal system.
- 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:
- Mouth parts- – type e.g. biting or piercing.
- Position of mouthparts – ventral or anterior.
- Wings – presence or absence; number of wing types, structure, texture.
- Size of legs.
Order Orthoptera
- Have biting and chewing mouthparts.
- Hind legs longer than other legs e.g. fore wings, leathery and longer than hind legs. e.g. locusts and grasshoppers .
- 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
- Bees, wasps, ants.
- They have sucking mouthparts, two pairs of wings which are membranous.
- Some are non-winged e.g. some ants.
- Bees are important in pollination i.e. in production of honey.
Order Isoptera – Termites
- They have biting mouthparts which are anterior.
- Most are wingless,
- Those with wings they are membranous and of the same size.
- They are important in nutrient cycling as they feed on cellulose.
Order Coleoptera – Beetles
- Have biting mouthparts,
- Two pairs of wings,
- Fore wing hardened enclosing membranous wings.
- Destruction of stored grains and legumes (pulses)
Phylum Chordata
- This name is derived from the term notochord.
- This is a long flexible rod-like structure.
- The more familiar chordates are known as vertebrates.
- In vertebrates the notochord exists only in embryonic stages of development which in later stages is replaced by a vertebral column.