ICSE Class 9: Phylum Invertebrata - Annelida, Arthropoda, Mollusca and Echinodermata Videos | Classification of Animals

The exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. 

The internal organs of molluscs are present in the hump.

Phylum Echinodermata includes spiny skinned organisms.

The locomotory organs of Echinoderms are called tube feet.