Question

Ascon type canal system is found in:
a. Grantia
b. Leucosolenia
c. Hyalonema
d. Euspongia

Answer 1

Hint: Porifera is the phylum which includes animals that have a porous body. They have diploblastic body type. In case of sponges, the body is vase shaped and it has many pores. They are called ostia. A terminal opening called ostium is present. A cavity is present called spongocoel, it acts as a common space for food and gaseous exchange.

Complete answer:
To answer this question, we must understand canal system:
A complex system of pores and canals is called a canal system. It is also called a water transport system. Water enters through ostia and then it can flow through the body, leading to spongocoel and it moves out through the osculum. Sponges are found in oceans except Spongilla.

The outer layer of cells is flat and are called pinacocytes.
Sponges show canal systems. It has few types which are-
Ascon type, Sycon type and Leucon type.
This canal system is based on the location of collar cells or choanocytes. Collar cells are spherical and have projection-like collars.

In case of ascon type, collar cells lie in spongocoel. It is the simplest type of canal system.
Example: Leucosolenia and other homocoela. Body has a large number of inner pores which are intracellular.

In case of sycon type, lie in radial canals. These are canals that are seen all along the body.
Example: Scypha and Grantia. It is more complex than ascon type. Ascon type is found in developmental stages which later develops to sycon type. There are incurrent and radial channels.

In leucon type, the collar cells lie in flagellated chambers. It is the most complex type of canal system. Canal system becomes irregular and in flagellated chambers. Water from exterior enters through ostia, into the incurrent canals through prosopyle, they reach the flagellated chambers. And then each the excurrent canals and then leaves the body through the osculum.
Example: Spongilla

Hence, The correct answer is option (B).

Note: The canal system is not an evolutionary trend. Canal system becomes complex to increase the body size. The efficiency of collar cells to manage water transport increases. The size of spongocoel is reduced in size.