In which group of animals is the coelom filled with blood?

Which among the following have an open circulatory system?
$(i)$ Arthropoda
$(ii)$ Mollusca
$(iii)$ Annelida
$(iv)$ Coelenterata

The locomotory organs of $Echinodermata$ are:

Identify the phylum for the following characteristics given:
$(a)$ Organisms with jointed appendages.
$(b)$ Organisms are generally flatworms.
$(c)$ Body is segmented.
$(d)$ Skin of organisms is full of spikes.

Identify and write the names of the parts labeled as $A, B, C$ and $D$ in the given figure of a seahorse in your answer book.

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