Question

Asymmetrical sponges mostly occur in
(a)Calcarea
(b)Hexactinellida
(c)Demospongiae
(d)All of the above.

Answer 1

Sponges are the simplest multicellular organism and make up the phylum Porifera. They are pore bearing aquatic invertebrates.

Complete answer:
Sponges of class Demospongiae have mostly asymmetrical sponges. The correct answer is Demospongiae.
Some examples of Demospongiae are cliona, chalina, euspongia, oscarella, etc. These are sponges with soft bodies that cover a hard massive skeleton. They have a different shape from the glass sponges if they contain spicules.

Additional Information: Let us know more about each class of sponges given in the question-
-Demospongia: These are mostly asymmetrical sponges containing a hard and massive skeleton. They include almost 76% of sponges. They are economically important as bath sponges that we use are made from them.
-Calcarea: These sponges are characterized by spicules made out of calcium carbonate. Commonly these spicules have three points but some species may have two or four points as well. They have a vase or cylindrical body and are radially symmetrical. Leucosolenia is an example of Calcarea.
-Hexactinellida: These sponges have a cup-shaped body and can be radially symmetrical. They have a skeleton made of 4 or 6 pointed siliceous spicules. An example of Hexactinellida is the glass rope sponges.
Therefore, the correct answer is demospongiae.

Note: The 3 classes of sponges are based on the composition of their spicules and skeletal fibers. Only Demospongiae are asymmetrical whereas the other two classes have symmetrical body structure. Demospongia is the most abundant living sponges containing 90% of known species of sponges. It is because their skeleton often consists of spongin fiber instead of spicules. Spongin is less rigid than the spicules.