Question

Choanocytes are the characteristic cells of
A. Sycon
B. Euspongia
C. Pennatula
D. Ctenoplana
E. Cliona

i. A and B only
ii. A, B, and C only
ii. A, B, and D only
iv. A, B, and E only

Answer 1

Hint: Collar cells or choanocytes are uniflagellate ellipsoid sponge cells with a transparent contractile collar. Collar cells or choanocytes are specific to the cells of porifera/sponges. In sponges, spongocoel and the canal are internally lined by choanocytes.

Complete step-by-step answer:
Choanocytes are also known as collar cells, they include the cilium or central flagellum, encircled by a collar of microvilli which are linked by a thin membrane. Choanocytes cells line the interior of leuconoid, syconoid, and asconoid body kinds of sponges. For example, Sclerocyte, Archeocyte, Oocyte, Porocyte, Lophocyte, Pinacocyte, and Mesohyl. Choanocytes have a circular cell body connected to the inside wall of the sponge and are also the position of the food vacuoles and cell's nucleus. Each choanocyte has one flagellum, which seems to be like a whip-like structure. This structure stretches from the centre of the cell out towards the open cavity of the sponge. All around this single flagellum is a cylindrical collar that is made up of several microvilli, which are very small finger-like projections on cells. The unique structure of choanocytes allows them to carry out various important functions within sponges. Euplectella, Cliona, and Euspongia are the different varieties of marine sponges. Spongilla is a kind of freshwater sponge.
Hence the correct answer is option d.

Note: Choanocytes are specialised cells that can offer different functions from mobility for the digestion in sponges. The main function of choanocytes is to help with circulation. The flagellum on each choanocyte whips backward and forwards, which creates water movement.