Page 26 - 11-Bio-10 Kingdom plantae

10. Kingdom Animalia eLearn.Punjab

Fig. 10.10 Arachtiids

4. Class Myriapoda:

The body is divided into large number of segments each having a pair of legs. A pair of antennae
and a pair of eyes are present on head e.g. centipedes and millipedes.

General organization of Arthropods

Arthropods have characteristics of higher forms such as bilateral symmetry, triploblastic, coelomic
cavity and organ systems and have reached the peak of invertebrate evolution. Two of their main
achievements are the chitinous exoskeleton and locomotary mechanism. These animals can walk,
swim and fly. The jointed appendages (limbs) have been modified or diversified for various uses in
the different sub-groups of Arthropoda.

Chitin is non-living, non-cellular and is secreted by the under lying epidermis. It is made of
polysaccharide.On the outer side of chitin,there is a waxy layer. In some Arthropods and in certain
parts in other Arthropods chitin is soft and flexible, in others it is hard. In general, it is for protection
but it also serves as lever for the movement of muscles of jointed limbs. The chitin in the jaws is
used for biting and crushing food. It also forms lens of the compound eyes the copulatory organs
and organs of defence and offence.

26
V: 1.1