Question

Rhagon type of larva is found in
A. Spongilla
B. Leucosolenia
C. Sycon
D. All of the above

Answer 1

Hint:-Larva is the active, but immature stage of an animal which will undergo a metamorphosis during its lifetime. The larval stage can be seen in most of the lower animals like sponges, insects, and chordates like frogs etc. It is the developmental stage which may or may not resemble the adult organism in morphology. They are usually seen in aquatic habitats.

Complete Answer:-
Spongilla is an organism coming under Phylum Porifera commonly known as sponges. Spongilla is a freshwater sponge. Sponges have indirect development. Common larval forms seen in sponges are parenchymula, amphiblastula etc. But the larvae of Spongilla are known as Rhagon type of larvae as they have a Rhagon type canal system.
The sponges arising from the rhagon stage have a broad base and it is conical in shape with a single osculum at the summit. They have a basal were called hypophare which lacks flagellated chambers. Upper wall has flagellated chambers called spongophare. Sponge of seal is bordered by oval flagellated chambers opening into it by apopyles.
Dermal pores or Ostia open into subdermal spacers which extend below the entire surface of the body. Branching incurrent canals lead from subdermal spaces into small flagellated chambers formed from radial canals. From flagellated chambers, excurrent canals lead into the spongocoel. Spongocoel opens by a single osculum.
Sycon have amphiblastula larva and Leucosolenia have parenchymula larva.

The correct answer is Spongilla, option (A).

Note:- Rhagon is the canal system seen in Spongilla larva. All the cavities or pores in the body of sponges, traversed by the water currents which nourish it from the time it enters through the pores until it passes out by osculum is collectively called a canal system. Different types of canal system are seen in different sponges. They are asconoid type, syconoid type, leuconoid type and rhagon type.