Question

Which of the following is pseudocoelomate?
(a) Nematoda
(b) Annelida
(c) Echinodermata
(d) Mollusca

Answer 1

Hint: Important characteristics of pseudocoelomate are they lack a vascular blood system, diffusion and osmosis circulate nutrients and waste products throughout the body, no segmentation, and possibly pedomorphism.

Complete answer:
In pseudocoelomate, the true coelom is not present. The blastocoel (the cavity of a blastula) is partly filled by mesodermal cells. The body cavity is lined by mesoderm only towards the body wall and mesoderm isn't present towards the gut.
Nematodes are pseudocoelomate as they show all the characters of a pseudocoelomate, they lack a vascular blood system. The diffusion and osmosis circulate the nutrients and waste products throughout the body of the organisms. No segmentation takes place in the case of Nematoda. They are possibly paedomorphism(slowing the physiological development of an organism) . E.g. Roundworms.
Annelids -The Annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms. They also have parapodia for locomotion. Species including ragworms, earthworms, and leeches.
Echinodermata - These animals possess a true coelom that is modified into a unique circulatory system called a water vascular system. The adults are organisms by their (usually five -point)  symmetry, and contain starfish, sea urchins, sand dollars, and sea cucumbers, also because of sea lilies or "stone lilies".
Mollusca - The animals in phylum Mollusca all have bilateral symmetry. Type of Coelom: Animals in Mollusca are coelomates. Examples of phylum Mollusca are Sea Hares, Sea Butterfly, Squid, Octopus, and cuttlefish.
So, the correct answer is ‘Nematoda’.

Note: In acoelomate, Coelom is absent. The blastocoel is completely occupied by mesoderm. E.g. Porifera, Coelenterate, and Flatworms (Platyhelminthes). There is only a spongocoel or coelenteron present.