Question

Which one of the following is not a class of phylum Porifera?

• A. Calcarea
• B. Hexactinellida
• C. Hydrozoa
• D. Demospongiae

Answer 1

Answer: (C)

Hydrozoa

Porifera is divided into three classes based on the skeleton they possess:
a. Calcarea - e.g., Sycon. This class includes sponges with skeleton made up of calcium carbonate containing spicules.
b. Hexactinellida - e.g., Euplectella. This class includes sponges with skeleton made up of silicon containing spicules.
c. Demospongiae - e.g., Spongilla. This class includes sponges with a skeleton made up of silicon-containing spicules or spongin fibers or both. On the other hand, Hydrozoa is a class of individually very small, predatory animals belonging to the phylum Cnidaria.

Thus, the correct answer is option C.