Crayfish is a

The biggest phylum in regard to the number of species is

In which of the following is an open circulatory system found?
$(1)$ Arthropoda $(2)$ Annelida $(3)$ Chordata

Spiders prepare their webs with the help of:

The largest phylum of the animal kingdom is .......

In many arthropods,the head and thorax are fused to form a cephalothorax. However,in which of the following classes of animals is the body divided into head,thorax,and abdomen?