Question

Sponges are mostly
(a) Radial
(b) Biradial
(c) Asymmetrical
(d) Bilateral

Answer 1

Hint: Sponges belong to the phylum Porifera. They are underwater organisms that lack true tissues and organs. They do not have a digestive or circulatory system and respiration takes place by water diffusion. And their life functions take place through central cavities and pores by diffusion. Hence, their symmetry will be decided by their functions and structure.

Complete step by step answer:
- Sponges, the representative organisms of phylum Porifera, are underwater multicellular animals full of pores and channels to allow water flow through them.
- They do not have a nervous, digestive, or respiratory system, and rely only on the flow of water through their entire body for the ingestion of food and the elimination of wastes.
- They have no real body layers except for the outer epidermis and the inner layer that consists of cavities.
So, the correct answer is ‘Asymmetrical’.

Additional Information:
- True animals can be divided into three groups based on their symmetry. The types of symmetry are radial symmetry, the arrangement of body parts around a central axis, like the pieces of a cake; bilateral symmetry, where the plane of division divides the animal into two equal halves; and asymmetry which is seen in Porifera.
- Sponges have both sexual and asexual methods of reproduction - the asexual reproduction occurs in three ways: after fragmentation, by budding, and by producing gemmules. In sexual reproduction, they behave as hermaphrodites. Sperm production and sometimes egg production is carried out by choanocytes. The released sperm from one sponge travels and if it comes in contact with another sponge, the fertilized eggs are formed. These fertilized eggs have different methods of being released, travelling, and forming new sponges.
- The structure of the sponge is held together by a soft endoskeleton known as mesohyl.

Note: - Some animals like sea stars start life with one type of body symmetry, but develop into a different type as adults. For example, in the case of sea stars, it is observed that at their adult stage they show radial symmetry still they are classified as bilaterally symmetrical. Flounder fish larvae are bilaterally symmetrical and adult fish are asymmetrical.
- The internal skeleton of sponges is made of spongin or spicules of calcium carbonate or silicon dioxide.
- Sponges are sessile, i.e., they do not have any movement.