Study of Pila -Dr. Vidhin Kamble Sangola College

 Classification and General Characters 

Phylum    -   Mollusca -             Soft bodied animal presence of hard calcareous  

                                                   shell

Class        -  Gastropoda            Foot in front of alimentary canal

Subclass   -  Prosobranchiata    Presence of gills or ctinidium

Sab-order -  Taenioglossa         Ctinidium act as respiratory organ

Genus       -  Pila

Species     -  globosa

Characters

 Pila globosa is commonly known as apple snail it is Yoni valve freshwater mollusc it is herbivorous and adapted for amphibious life in water and on land.

1. The body the soft and protected by thick lemon yellow brownish or blackish calcareous shell.
2. The shell is elongated hollow cone, spiral coilled circular around central axis called as collumela.
3. The single revolution of sale around the central axis is called as whorl. 
4. There are usually 6 and half whorl. the top of a shell is icalled as Apex and the largest whorl close to the mouth is called as body whorl.
5. The shell is marked by Mini lines of growth the vertical lines on shell are called varices (single-varix).
6. The sexes are separate.
7. The body whorl open outside by wide opening called as mouth, situated on ventral side, covered by a lid or operculum
8. The region between two whorl is called suture.  

Digestive system of Pila :

The digestive system consists of a long curved tube extending from the mouth to the anus. It is broadly differentiated into

1.      Fore gut,

2.      Mid gut

3.      Hind gut 

  

Fore gut:

The fore gut is ectodermal in origin and consists of

1.      Mouth

2.      Buccal mass

3.      Oesophagus.

Mouth:  is a median vertical slit situated at the anterior end of the snout that leads into a thick walled muscular buccal mass.

The buccal mass encloses a cavity known as buccal cavity which contains two jaws and a radula. At the entrance of the mouth is a pair of chitinous jaws.  The jaws bear numerous small and two or three large teeth.

The buccal cavity shows  chitinous ribbon shaped organ called radula. Posteriorly, it is enclosed in a sac called the radular sac.

The radula bears numerous backwardly directed horny teeth arranged in transverse rows.  In Pila each transverse row possesses seven teeth, a median rachidian teeth, on its either side one lateral teeth and two marginal teeth, giving the formula 2, 1, 1, 1, 2 

 The teeth are pointed with sharp edges and are used like a saw for cutting the food. The radula is moved forward and backward, up and down with the help of protractor and retractor muscles and act as a rasping organ.

A pair of salivary glands are present on the sides of the buccal mass and their ducts open into the buccal cavity. The secretions of the salivary glands contain mucus and an enzyme which digests starch. The mucus lubricates the radula and helps in the transport of food. 

Dorsally, the buccal mass leads into a long narrow oesophagus. Just below the salivary  glands, near the origin of the oesophagus are a pair of round oesophageal pouches, probably secrete digestive enzymes. Mid gut:

Mid gut is endodermal in origin and consists of stomach and intestine. Oesophagus opens into the stomach. It is red in color. The stomach consists of two parts:

1. Cardiac chamber and

 2. Tubular pyloric chamber.

The oesophagus opens into the cardiac chamber. The cardiac chamber constitutes the main part of the stomach and possesses longitudinal folds on its inner surface while the pyloric chamber has transverse folds on its inner surface.

The intestine is long and forms 2 ½-3 coils. A short, round blind pouch called the caecum arises from the pyloric chamber and opens at the junction of the stomach and the intestine. Lying in the visceral mass is the digestive gland (often referred to as the hepatopancreas or the liver) which is dirty brown in color

The digestive gland contains three types of cells:

1. Secretory cells: they secrete cellulose digesting enzymes.

2. Resorptive cells: they digest proteins intracellularly.

3. Lime cells: they store calcium phosphate.

Hind gut:

The posterior part of the intestine is straight and thick walled and is called the rectum. It terminates in an anus which is situated near the mouth on the right side of the head The hindgut is ectodermal in origin.



Nervous System of Pila Globosa: 
The nervous system of Pila globosa is ganglonated type,  consists of paired and unpaired ganglia with their commissures and connectives. The commissures are the connections between similar ganglia, while connectives are the nerves which connect two dissimilar ganglia.

The paired ganglia of Pila are

1       Cerebral ganglia

2       Buccal ganglia

3       Pleural ganglia  

4       Pedal ganglia

5       Visceral ganglia,

Unpaired ganglia are

              1.     Supra-intestinal ganglia

              2.     Infra-intestinal ganglia

1. Cerebral ganglia:

These are two triangular cerebral ganglia, present on dorslo-lateral side above the buccal mass. These ganglia are  connected to each other by transverse connection called commissure above the buccal mass. Cerebral ganglion are also connected with the buccal ganglion of its side through a connection called  cerebro-buccal connective.  Cerebral ganglia aslo connected with pleural and pedal ganglia by thick band-shaped cerebro-pleural and cerebro-pedal connectives of the corresponding side.

Cerebral ganglion gives off several nerves anteriorly to the skin of snout, the tentacle, the buccal mass, the eye and the statocyst.

2. Buccal Ganglia:

Buccal ganglia are present at the junction of the buccal mass and oesophagus in the form of pair. These ganglia are connected to each other by a transverse connection called buccal commissure. They are also connected to the cerebral ganglia by a cerebro-buccal connective on each side. The buccal ganglia supplies nerves to the buccal mass, radular sac, salivary glands, oesophagus and the oesophageal pouches.

3. Pleuro-pedal ganglionic Mass:

The Pleuro-pedal ganglionic Mass is formed by the fusion of the pleural and pedal ganglia of each side lies just below the buccal mass. In a pleuro- pedal ganglionic mass, the pleural ganglion is placed towards the outer side and the pedal ganglion to the inner side. The pleuro-pedal ganglionic mass is connected to the cerebral ganglion of its side by a connection called cerebro-pleural connective and cerebro-pedal connective, respectively. While the two pedal ganglia are connected to each other by two pedal commissures. To the right pleuro-pedal ganglionic mass, infra-intestinal ganglion is fused. A delicate loop-like infra-intestinal nerve  behind the pedal commissure, connects the pleural ganglia of both the sides.

4. Supra-intestinal ganglion:

The supra-intestinal ganglion is situated behind the pleuro-pedal mass of the left side. Supra-intestinal ganglion is connected with the pleuro-pedal ganglionic mass by a connective, called zygoneury. It gives thin supra-intestinal nerve on inner side which joins to the right pleural ganglion.

The supra-intestinal ganglion  is also connected to the visceral ganglion with visceral connective

5. Visceral ganglion:

The visceral ganglion is formed by the fusion of two spindle-shaped ganglionic masses. The visceral ganglion lies near the base of the visceral mass close to the anterior lobe of the digestive gland. The visceral ganglion is connected with the supra-intestinal ganglion by a delicate supra-intestinal or left visceral connective. It is also connected with the right pleural and infra-intestinal ganglion through the infra-intestinal or the right visceral connective.

 Osphradium of Pila

Location : It is a single, somewhat elongated structure suspend from the roof of mantle cavity close to the the left nuchal lobe or inhalant siphon.

Structure  It is small elongated oval structure it is broader in in middle and at the right end it is bluntly rounded oval structure the left side is is somewhat pointed it consists of 22 to 28 thick fleshy roughly triangular leaflets.  On median or central axis each leaflet is attached to the mantal wall bye its broad base and the central axis by it's smaller inner side
Osphradium is supplied by nerve from the left plural ganglion.

Function :  it helps in to check the physico-chemical nature of water. that is it check  the quality of water. 





Radula of Pila

Location :
1. The radula is present in bucal cavity placed on a pair of radular cartilages operated by large radu­lar muscles,

Structure :
2.  Numerous transverse rows of teeth are present on the radular ribbon.
3. The teeth in a transverse row are one median or rachidian, one lateral and two marginal,
4. the radular formula being 2. 1. 1. 1. 2.
5. Distally, the radular teeth bear broad cutting edge 


Function 

The teeth are pointed with sharp edges and are used like a saw for cutting the food.
The radula is moved forward and backward, up and down with the help of protractor and retractor muscles and act as a rasping organ.