The biggest phylum in regard to the number of species is

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

In which animals is an open circulatory system seen?

Which of the following is $NOT$ a characteristic of the phylum $Arthropoda$?

Which phylum is the largest phylum of the animal kingdom?

Moths and butterflies come under which insect order?