These are the most successful group of animals. They outnumber all other animals in population strength. The body is segmented. It is covered by a hard exoskeleton made of chitin. During growth the exoskeleton is shed (moulting of ecdysis). The legs or paired appendages are jointed.
Phylum : Arthropoda :-
These are the most successful group of
animals. They outnumber all other animals in population strength. The body is
segmented. It is covered by a hard exoskeleton made of chitin.
During growth the exoskeleton is shed (moulting of ecdysis). The legs or paired
appendages are jointed. The head region has a pair of prominent compound
eyes. Each compound eye is made up of several photoreceptor sub units called
They have an open circulatory system without
vessels. The body cavity is filled with a fluid called haemolymph.
Such body cavity is known as haemocoel. These are unisexual, exhibiting sexual
dimorphism. The young forms produced are invariably called the larvae.
The larvae undergo metamorphosis and develop into adults.
This Phylum comprises five Classes, Class
Onychophora: It includes small worm like Peripatus. Peripatus shows
Annelidan and Arthropoda characters. Hence this may be considered as a connecting
link between the two groups.
Class Crustacea :- The examples for this class are prawns, crabs and lobsters.
The dorsal body surface is covered by a sheild like carapace.
Class Myriapoda :- It includes centepedes and millipedes.
These organ-isms have a distinct head and simple eyes. The centepedes have a
pair of poison claws. The body consists of numerous segments,
bearing pairs of legs.
Class Insecta :- It comprises the common insects. The body
is divided into head thorax and abdomen.In several insects, the
adults have two pairs of wings on the thorax. Respiration happens through the
Class Arachnida :- It includes scorpions, spiders, ticks and mites.
The body is divided into cephalothorax and abdomen.
There are four pairs of legs attached to the cephalothorax.
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BIOLOGY (ZOOLOGY) Standard XI first year 11th text book Assignment topics question and answer Explanation Definition : Phylum : Arthropoda |