Characteristics of subclass 2-OPISTHOBRANCHIA of Gastropoda

1) They are exclusively marine gastropods.

    2) They have reduced type of shell and when present 

         often covered with mantle or pedal folds.

    3) They do not have operculum usually.

    4) They have single gill or often replaced by secondary 

         branchiae in the form of dorsal outgrowth.

        5)They have heart with one auricle posterior to the

            ventricle.

        6)They have mantle cavity rotated to right side or often

             lost due to detorsion.

                7)They have nervous system concentrated due to

                    detorsion.

                8) They are hermaphrodite.

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Characteristics of order3 –Stenoglossa of subclass-PROSB RANCHIA

1)They have shell with more or  elongated siphonal canal.

2)They have radula which consist of rows with two or three teeth in each rows.

  Examples: Murex, Magilus, Buccinum, Meulongena,Conus and Teregera.

 Conus geographus

Parts of Conus geographus

Murex

Magilus

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Characteristics of order2 –Mesogastropoda of sub class PROSOBRANCHIA

1)    They are the Prosobranchia with siphon, penis  and 
        non –calcified Operculum.

2)    They have radula of taenioglossare type with 7 teeth   
        in each row.

3)    They have one monopectinate gill.

4)    They have heart with one auricle.

5)    They have one ospharadium and  nephridium.

6)    They have nervous system concentrated without pedal cords.

Examples:-Viviparus, Ampullarius, Pila, Valvalata, Truncatella, Littorina, Hydrobia, Jonthina,Cypraea.

Viviparus

Ampullarius 

Ampullarius gigas

   
        

Cypraea

Hydrobia

Littorina

Littorina

Cypraea.

Cypraea.



 

         

Characteristics of order –Archaeogastropoda of sub class PROSOBRANCHIA

1) They are the Prosobranchia without proboscis, siphon,penis  

    and prosrratic glands.

2) Operculum is also present in many forms with few exception.

3) They have one or two bipectinate internal gills.

4)  They have heart mostly with two auricles.

5)  They usually have two osphradia.

6)  They have two nephridia.

7)  They have nervous system which is not concentrated and usually with two pedal cords.

8) They discharge the sex cells directly into the sea by the right nephridia.
Examples:-Haliotis, Fissurella, Acamaea, Patella, Trochus, Asteraea. Turbo.
        

Fissurella volcano

Patella

Trochus snail

                                                    

Characteristics of subclass of Mollusca-PROSOBRANCHIA

1)    They are mostly marine ,few freshwater or terrestrial forms.

2)    They have visceral mass twisted.

3)    They have mantle cavity which opens anteriorly in front of the visceral mass.

4)    They generally have conical and spirally coiled  shell with an operculum.

5)    They have distinct head with snout bearing a pair of tentacle and a pair of eyes.

6)    They have muscular foot that forms the ventral part of the body.

7)    They may have ctenidia or gills and if present are situated in the front of the heart.

8)    Sexes are separate

Characteristics of Mollusca’s class-GASTROPODA

1)    They are marine, freshwater, terrestrial and few parasitic on echinoderms. 

2)    They have unsegmented, asymmetrical  body with a univalve, spirally coiled shell. 

3)    They have distinct head with tentacles, eyes and mouth. 

4)    They have foot which is ventral, broad, flat and muscular forming the creeping sole and often bearing dorsally a hard piece, the operculum on its posterior end. 

5)    They have visceral mass spirally coiled exhibiting torsion. 

6)    Mantle is a collar-like fold of body wall, lining the body whorl leaving a space, the mantle cavity ,between itself and the body. 

7)    They have Buccal cavity containing an odontophore with radula bearing rows of chitinous teeth. 

8)    They have digestive system consisting of a muscular pharynx, long oesophagus, stomach, long coiled intestine and anteriorly placed anus. 

9)    Most of them respire through gills(ctenidia ) ,some of them through the wall of the mantle cavity and many by lungs. 

10) They have open circulatory system with heart enclosed Pericardium

11) They have excretory organs  consisting of metanephridia which are paired in primitive forms and reduced to a single nephridia in most forms.
12)They have nervous system comprising of distinct cerebral and pleural besides buccal, pedal, parietal and visceral ganglia.

13)Most of them have sexes in two bodies(dioecious) but few have both the sexes in same body.

14) The development  includes trochophore and veliger larval stage.                            

Characteristics of Mollusca class- MONOPLACOPHORA

 The word Monoplacophora is derived from three Greek words monos=one, plax=plate and pherein=bearing. So it includes animals having only one plate. It does not have any order.The characteristics of it are listed as below.

1)    They have bilaterally symmetrical and segmented body.

2)    They have shell made up of single piece or valve.

3)    They have head without eyes and tentacles.

4)    They have ventral and flat foot.

5)    They have mantle which encircle the body as a circular fold of the body wall.

6)    They have external and serially arranged gills.

7)    They have five pairs of serially arranged nephridia.

8)    They have sex organs in two separate bodies.

Examples :- Neopilina galatheae

Neopilina galatheae

Charcteristics of orders of class Polyplacophora with examples

a) Order1:Lepidopleurida

i) They have shell with valves that are not provided by 

   insertion plates or if present without insertion teeth.

   Examples:- Lepidopleurus, Hnleya

Lepidopleurus

  








        

 b) Order2:- Chitonina

             i) They have shell with valves that are provided by 

               insertion plates and insertion teeth.

     Examples:-Tonicella, Chiton, Cryptlchiton,Choneplex

Tonicella lineata

chiton

      

Characteristics of mollusca class-POLYPLACOPHORA with orders

       The word Polyplacophora is derived from three Greek words poly=many, placo=plate and pherein=bearing. Thus this class includes animals which have many plates. This class has two orders which are named as follow

a)    Order1:-Lepidopleurida

b)    Order2:- Chitonina

The characteristics are listed as below.

1)    They are mostly bilaterally symmetrical, dorsoventrally flattened mollusks.

2)    They have elliptical, convex dorsally and flattened ventrally body.

3)    They have distinct head without eyes and tentacles.

4)    They have shell composed of a longitudinal series of eight calcareous pieces.

5)    They have foot flat and ventral ,laterally bordered by a groove containing gills.

6)    They have well developed radula  having 17 teeth.

7)    They have coiled intestine with a terminal anus.

8)    They have a pair of nephridia extending from pericardium to the lateral groove.

9)    They have a pair of gonoducts without relation to the pericardium.

   10 ) They have sex organs in two separate body(dioecious).

Characteristics of orders of Aplacophora with examples

      Order1:- Neomenioidea

a)    They have mid-ventral longitudinal groove.

Examples:- Neomenia,Proneomenia,Lepidomenia

       Order2:- Chaetodermatoidea

a)    They donot have mid-ventral longitudinal groove.

Examples:- Chaetodermia , Prochaetoderma