Question

Limax and Helix respire with the help of
(a)Ctenidia
(b)General body surface
(c)Pulmonary sac
(d)Buccal Cavity

Answer 1

In terrestrial molluscs the respiring organ is reduced. The respiring organ is an evolved structure in all terrestrial organisms. Respiration takes place in the respiratory (mantle) cavity. The inner surface of this cavity is highly vascularised. Terrestrial molluscs belong to the class Gastropoda.

Complete answer:
Gastropoda includes all the land snails and land slugs. Helix pomatia is a land snail. Limax cinereoniger is a land slug. Terrestrial molluscs respire with the help of pulmonary sac. The pulmonary sac is a hollow organ situated in the mantle cavity with a contractile exterior opening that functions as a lung in terrestrial molluscs.

Additional Information: -Rasping organs, radula are present in molluscs.
-The circulatory system is open type.
-A ctenidium is a respiratory organ or gill found in molluscs.
-A ctenidium is shaped like a comb or a feather, with a central part from which many filaments are lined up in a row which protrudes hanging into the mantle cavity and thus increasing the area available for gaseous exchange.
-The respiration taking place through the buccal cavity is called buccopharyngeal respiration. The buccal cavity is rich in moist mucous membrane and is richly supplied with blood capillaries.
The oxygen is absorbed via partial diffusion.
So, the correct answer is ‘Pulmonary sac’.

Note: -Respiratory organs of aquatic molluscs consist of numerous ctenidia usually provided with osphradium at the base whereas the lung (pulmonary sac) is only developed in the terrestrial forms.
-General body surface respiration is found in lower organisms like in annelids and nematodes.