Question

What is a pseudocoelom? What are the advantages of having a coelom? Name the invertebrate phylum that has a pseudocoelom.

Answer 1

Hint: Higher organisms like vertebrates have a body cavity known as a coelom that runs down centrally through the organism. The coelom is between the body wall and the intestinal canal and is completely surrounded by mesodermal tissue.

Complete Answer:
- While the coelom is within the mesoderm, the pseudocoelom is between the mesoderm and endoderm layers. It is also a fluid-filled cavity, and does surround the internal organs. During embryonic development, the blastocoel gives rise to the pseudocoelom. Unlike animals with a coelom, it cannot be compartmentalised and it does not have peritoneal tissue demarcating it.
- There is a distinct advantage to having a true coelom. Being fluid filled, it allows for a more rigid structure due to the hydrostatic properties of the fluid, making the skeletal system much more efficient. It also helps with waste removal, circulation, better digestion, shock absorption for the internal organs, and it can be compartmentalised.
- One of the most well-known coelomates is the ubiquitous earthworm. Belonging to the phylum Annelida, the earthworm’s coelom forms a proper hydrostatic skeleton to which the longitudinal and circular muscles are attached.
- One of the invertebrate phylums that have a pseudocoelom is the Aschelminthes. In this phylum there are 6 sub-phyla which include the Nematodes, Rotifers, and Acanthocephalans.

Note: Humans are also coelomates. The cavity is divided into separate sections in the body during development. As deuterostomes, the blastopore develops into the anus, while in protostomes it develops into the mouth.