Which phylum includes the largest number of animals?

To which of the following classes does $Limulus$ belong?

$A$ student has identified a triploblastic,coelomate,segmented animal as an arthropod. Which additional character should the student have verified before identifying that animal as an arthropod?

Exoskeleton of which phylum consists of a chitinous cuticle?

Which one of the following belongs to phylum $Arthropoda$?

Identify the gregarious pest.