The skeleton is made entirely of cartilage in:

The animals having a two-chambered heart belong to the class:

The locomotory organs of $Echinodermata$ are:

Protochordates possess a notochord in larval forms. Appraise the use of this feature in these animals.

State the reason for the following:
$(i)$ Nematodes have a pseudocoelom.
$(ii)$ Arthropods have an open circulatory system.
$(iii)$ Echinoderms are named as such.

Identify a member of the phylum Porifera.