Hint: It is a characteristic feature of metazoans. It is formed during the embryo development from the three germinal layers. It is a fluid-filled body cavity that is present between the alimentary canal and the body wall. It also has a mesodermal origin which is lined by mesoderm.
Scorpion - The true body cavity that is coelom is possessed by the Scorpion belongs to the group Arthropoda. It is the body cavity that is present between the mesoderm and the endodermal layer. It provides a hydrostatic skeleton and helps in absorbing the shock. The muscles of the body wall grow independently with the help of coelom.
Octopus - They are the most intelligent and flexible of all the invertebrates. They are cephalopod mollusks of the order Octopoda. The true coelom is possessed by all the advanced invertebrate phyla.
-Octopus has an internal body cavity that is a true coelom that is enclosed by measuring thermal membranes. Sometimes It is reduced to a small space around the heart known as a hemocoel.
Additional Information: Tapeworm - The worms that are flat in shape belong to the phylum Platyhelminthes and most of them are parasitic in nature.
-Parenchyma is the tapeworm middle tissue layer which is a loose mesoderm and splits into a cavity.
-The tapeworm and the other animals in this phylum without a coelom are known as acoelomates.
Cnidarians - They don't have coelom because they are diploblastic means they don't have mesoderm tissue.
-This file is generally composed of aquatic animals like jellyfish, anemones, and corals.
-They have cnidocytes, a type of stinging cell.
So, the correct answer is, “C and D have a true coelom”.
Note: -The main body cavity in most animals is known as coelom which is present inside the body to surround and include the digestive tract and other organs.
-In the embryonic mesoderm, it arises as a cavity. The true coelom is present in Echinodermata, Annelida, and Arthropoda, Chordata, mollusk.
-The phylum Coelenterata and the phylum Platyhelminthes don't have a true coelom, that is they are acoelomates.