Complete information on the morphology pila

Pila is commonly known as apple snail. It is found in Oriental and Ethiopia regions.

Systematic Position:

Phylum – Mollusca – because of having soft body enclosed by a mantle.

Class- Gastropoda – Asymmetric body with a spirally coiled shell.

Genus – Pila

Species – globasa

Habitat:

Pila is fresh water mollusca. It lives in ponds, tanks, rivers, wells and paddy fields. It also lives in land. So it is an amphibious animal.

Habits:

Pila is herbivorous. It creeps very slowly with its massive foot. It respires with gills when in water and with lungs when on land. It can stand long periods of droughts by remaining dormant within its shell, buried in mud (summer sleep) sexes are separate. Breeding takes place in the rainy season. Fertilization is internal. Development is direct (No larval stages).

Morphology:

Shell:

The soft body of pila is covered by a Calcareous shell. It is spirally coiled. The coils of the shell are called whorls. The upper whorl is called apex. The apex is the first formed whorl. The lower most whorls are larger called body whorl. The body whorl is the youngest whorl. The line contact between whorls called sutures.

The surfaces of the whorls are marked by vertical ridges called lines of growth. A few lines of growth are prominent and they are called varices (singular-varix). The varices represent seasonal cessation of shell secretion by the mantle. The shell opens out by a large opening called shell mouth. The margin of the mouth is called peristome or lips. It is formed of inner lip and outer lip.

If the shell is held with the apex away from the observer, the mouth is towards right. The shell of pila is dextral. Rarely it may be sinistral i.e. the mouth is towards the left. The shell mouth is closed by a lid called operculum. The outer surface of the operculum contains concentric lines of growth around a central nucleus. The inner surface of the operculum has a boss, an elliptical area surrounded by a shallow groove.

The boss serves for the attachments of muscles that operate the operculum. The collumella, the central axis of the shell, is hollow and twisted. It opens to the exterior by a small opening called umbilicus. This opening is located near the inner lip of the peristome.

Body:

The body of pila is soft. It is divisible into 3 parts- anterior head, ventral foot and dorsal visceral mass. The head and fott are protruded from the shell for creeping but the visceral mass always remains within the shell. The body is firmly attached with shell by a strong columellar muscle.

Head:

The head beals two pairs of tentacles: anterior cephalic tentacles and posterior true tentacles. The head also bears a pair of eyes. The eyes are borne on a stalk called ommatophores.

Foot:

The foot is ventral and highly muscular. It has a flat smooth ventral surface called sole. The sole is applied to the substratum for creeping. The foot has two parts: anterior protopodium and posterior metapodium. The operculum is attached to metapodium.

Visceral mass: The visceral mass is the largest part of the body. It is coiled spirally like the shell. During embryonic development one side of the visceral mass grows faster than the other. The uneven growth causes the visceral mass to rotate up to 180 degrees. So that anus and mouth remain at the same side. This is called torson. Torson is the most distinctive characteristics of the class gastropoda (e.g. pila) during embryonic development. The visceral mass contains all the organ systems.

Mantle of Pallium:

The entire visceral mass is covered by a fold of skin known as mantle or palium- a characteristic organ of mollusca. The mantle secrets the shell. On the either side of the head, the mantle is produced into a highly contractile process called nuchal lobe or pseudo-epipodium. The left pseudo-epipodium is larger and rolls into a tubular respiratory siphon for air breathing.

Mantle or Palial Cavity:

Between the free margin of the mantle and the body there is a wide space known as mantle cavity. The mantle cavity contains a number of organs.

Pallial complex: The mantle cavity contains a number of organs collectively called mantle complex or pallial complex and includes epitaenia, pulmonary sac or lung, ospharadium. Ctenidium or gills, rectum, genital duct and anterior chamber of the kidney.

1. Epitaenia: It is a prominent ridge. It runs from the base of right nuchal lobe to the posterior end of the cavity. It divides the mantel cavity into two unequal regions: a right branchial chamber and a large left pulmonary chamber.

2. Pulmonary sac (lung): It is a large bag hanging in the mantle cavity from the roof of the mantle. It opens to the mantle cavity by a pulmonary aperture.

3. Osphradium: It is a small leaf like structure attached to the roof of the pulmonary chamber near the left nuchal lobe. It is olfactory in function.

4. Ctenidium or gill: It is the gill used for aquatic respiration. The gill lamellae are arranged on the one side of the axis. This type is known as monopectinate ctenidium. It lies in the extreme right side of the mantle cavity.

5. Rectum: It runs parallel to the ctenidium. It opens to the mantle cavity by anus.

6. Genital duct: The genital ducts: oviduct in the female and vas deference in the male run parallel to the rectum. The external opening of the genital duct is located near the anus. In male the penis lies close to the genital opening. At the base of the penis, there is glandular organ called hypobranchial gland.

7. The anterior chamber of the kidney: It is a reddish mass lies near the posterior end of the epitaenia. It opens by a small slit like aperture.