Question

Spongilla is
(a) Brownish
(b) Greenish
(c) Whitish
(d) Purplish

Answer 1

Hint: Spongilla belongs to phylum Porifera whose colour is influenced by its symbiotic relationship with an alga that lives intracellularly in its host. Phylum Porifera is commonly known as pore-bearing animals or sponges.

Complete answer:
Spongilla is a freshwater sponge which is found both in clear sunlight or under the rocks and logs. When growing in the sunlight, Spongilla is bright green due to the presence of Zoochlorella, which are green algae that live symbiotically with any invertebrate or protozoans. Zoochlorellae use CO₂ and nitrogenous and phosphorus wastes, offering oxygen and beneficial nutrients to their hosts.
Some important characteristics of Porifera are as follows:
- Level of organisation: Sponges are primitive multicellular animals with a cellular grade of organisation.
- Body form: Their body is porous with mainly two types of pores i.e. inhalant pores referred to as Ostia and exhalant pores referred to as oscula. Ostia leads to a central cavity, spongocoel, through a system of canals. Spongocoel opens to the external environment via one or two oscula.
- Skeleton: An internal skeleton is present which may consist of calcareous(of Calcium) or siliceous (of Silica) spicules or of fine spongin fibres.
- Canal System: A complex canal system in Spongilla maintains continuous water current flowing into the spongocoel. The canal system helps in nutrition, excretion, reproduction and respiration.
So, the correct answer is ‘greenish’.

Note: Spongilla which grow on the undersides of rocks or logs are usually pale coloured due to the absence or low densities of zoochlorellae as they are not well exposed to the sunlight. Zoochlorella in green Spongilla is found to be predominantly intracellular, i.e. reside in membrane-bound vacuoles of the host(in this case Spongilla). Sometimes the zoochlorellae are digested by the host which may have entered the cavity through the water canal system.