Corals are

Which group of animals have haemocoel?

Justify giving one reason: crocodiles have a four-chambered heart,but are still classified as reptiles.

State whether the following statement is true or false:
The animals belonging to phylum Nematoda contain only tissues and no real organs.

You are given leech,Nereis,Scolopendra,prawn,and scorpion; all have a segmented body organization. Will you classify them in one group? If no,give the important characters based on which you will separate these organisms into different groups.

State reasons for the following:
$(a)$ Mammals have mammary glands.
$(b)$ Annelids have a true body cavity.
$(c)$ Fish possess gills.