Two important mechanism of respiration in pila snail

Important mechanism of respiration in pila snail are given below:

1. Aquatic respiration:

When Pila submerged in water, it is adapted for aquatic respiration. At this time the head and foot of the animal is fully extended.

Both the nuchal lobes form channel-like structure. Water current enter through left lobe, tested by osphradium, goes to the posterior part of the pulmonary chamber, baths epitenia and finally enters the branchial chamber. After some time it flows out through the right nuchal lobe.

Flow of water current is maintained by

Image Source: 185.26.182.219

(i) The alternate lowering and raising of the floor of the mantle cavity, this is brought about by alternate protrusion and retraction of the head and

(ii) By the beating of cilia on the lamellae of the ctenidium.

2. Aerial respiration:

This mode of respiration is observed in both the conditions when animal is in water or on land. When it is in water, its left nuchal lobe makes a tube-like structure called siphon and it remains near the water surface.

Air enters mantle cavity through siphon and then goes to pulmonary sac through pulmonary aperture.

Air returns back from the same path. To maintain the flow of air inside and outside the alternate expansion and contraction of the pulmonary sac takes place.

Epitenia is raised to push the mantle wall and hence air is not allowed to enter the branchial chamber. Wall contains blood vessels and sinuses whose blood takes up 0₂ of the air and gives out CO₂

When the snail travels on land for some purpose it may breath air by the pulmonary method, without forming a siphon. During aestivation it breaths only by the air which is stored in the pulmonary sac.

Generally, the two modes of respiration go on alternately but one mode of respiration may be preferred on the other depending upon the prevailing conditions.