Question

station #3: grantia cross - section

1. label the cross - section of the grantia sponge below. label the following structures on your sketch above using the text book: osculum, choanocyte, central cavity
2. add arrows to your sketch above to illustrate the flow of water through a sponge.
3. what sponge body form is the sponge above? ascon, sycon, or leucon? (use your notes or the text book for help!)
4. what does the body form have to do with filtering ability? explain.

Explanation:

1. To label: Osculum is the large opening through which water exits. Choanocytes are collar - shaped cells that line the inner surface and create water flow. Central cavity is the large inner space.
2. Water enters through small pores (ostia) and flows towards the central cavity and then out through the osculum. Arrows should be drawn from outside in through ostia and then out through the osculum.
3. The sponge in the image has an Ascon body form which is the simplest form with a single central cavity and a thin body wall.
4. The more complex the body form (from Ascon to Sycon to Leucon), the greater the surface area for choanocytes. A larger surface area means more choanocytes can filter water, increasing the filtering ability. For example, Leuconoid sponges have a highly branched canal system and a large surface area for filtration compared to Asconoid sponges.

Answer:

1. Label osculum at the top opening, choanocytes on the inner - lining cells, central cavity as the large inner space.
2. Draw arrows entering through small pores (ostia) on the body surface and exiting through the osculum at the top.
3. Ascon
4. More complex body forms increase surface area for choanocytes, enhancing filtering ability.