o level biology notes

Phylum Arthropoda
PHYLUM ARTHROPODA

This is the phylum with the most number of animals  (arthras-jointed ,pod-feet.

Characteristic  features

Have jointed appendages which include legs and other body out growths e.g antennae
Have an open blood circulatory system
Have bodies which are segmented i.e with distinct divisions
Have a bilateral symmetry
 Have a developed nervous system located ventrally on the body
They shed off their exo skeleton to allow growth
This phylum is divided into four classes basing on;

 Number of limbs
 Number of body divisions
 Presence of antennae
 Number of antennae
The four classes of this phylum are;

Insecta

Arachnida

Myriapoda

Crustacea



CLASS EXAMPLES NUMBER OF BODY DIVISIONS NUMBER OF LEGS NUMBER OF ANTENNAE
Insecta Grasshoppers ,housefly, bees ,beetles 3 6 2
Arachnida Spiders, ticks, mites, scorpions 2 8 None
Crustacea Woodlice, crayfish,  lobsters, water flea 2 10 or more 4
Myriapoda Centipedes, millipedes Many body segments with head Many 2
CLASS INSECTA

Insects have the following characteristics

The body is divided into three body parts, namely; head, thorax, and abdomen
They have three pairs of legs on the thorax
They have a pair of compound eyes except the soldier termites
Adults have one or two pairs of wings except some few members
They breath through the spiracles and gases reach the body cells through the tracheal system
The thorax is divided into three main parts i.e. prothorax, mesothorax, and metathorax


CLASS ARACHNIDA

Arachnids have the following characteristics

They do not have wings
Its body is divided into two parts i.e cephalothorax and abdomen
It has four pairs of legs attached to the cephalothorax
It has no antennae
It has simple eyes
It breathes by means of the lung book located in the abdomen
Its mouth parts are segmented and end in

CLASS CRUSTACEA

They have the following characteristics

They are aquatic or live in damp places
They use the gills and body surface for breathing
They have two pairs of antennae
They have two body divisions namely; cephalothorax and abdomen
CLASS MYRIAPODA

They contain the following characteristics

It has an elongated body with many legs
It has one pair of antennae
It breathes through the spiracles
It lives on land
It has many body segments
It has simple eyes
DIFFERENCES BETWEEN CENTIPEDES &MILLEPEDES

CENTIPEDES MILLEPEDES
Have fewer body segments Have many body segments
Have one pair of legs per segment Have two pairs of legs per segment
Have poison claws Have no poison claws
Are carnivorous Are herbivores
Do not coil They coil