Question

Choose the organism which has true coelom:

• A. Tapeworm
• B. Wuchereria
• C. Planaria
• D. Nereis

Answer 1

The correct option is D Nereis

Coelom is a cavity lined by mesoderm and is present between the alimentary canal and body wall. The organisms that have true coelom are triploblastic, i.e. ectoderm, mesoderm, and endoderm. All the organisms in phylum Annelida and its following phyla have true coelom. Organisms in the phylum Annelida are the first coelomate animals. Nereis belongs to phylum Annelida.

Organisms in phylum Platyhelminthes and Aschelminthes are also triploblastic but they don’t have a true coelom. Tapeworm and Planaria are flatworms and are a part of phylum Platyhelminthes. They are acoelomates, i.e. body cavity is absent. Wuchereria is a part of phylum Aschelminthes and is a pseudocoelomate, i.e. the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm.