characteristics of Class -PELECYPODA of MOLLUSCA

The word PELECYPODA  is derived from two Greek words pelekys=hatchet and podos.The characteristics 

 can be listed below.

 1. They are aquatic, mostly marine and some freshwater forms.

 2. They have bilaterally symmetrical and laterally compressed.

 3. They do not have distinct head.Pharynx,jaws,radula and    
     tentacles are absent.

 4. They have shell consisting of two lateral valves,hinged
     together mid-dorsally.

 5. They have ventral foot,muscular that is used for plough
     share.

 6. They have bilobed mantle consisting of paired, right and left
     lobes.

 7.They have paired gills or ctenidia one on each side.

 8. They have dorsally placed  reduced coelom.

  9.They have coiled alimentary canal with paired digestive
     glands.

10. They have heart in pericardium and consist of median ventricle and two auricles.

11.They have paired nephridia or kidneys that open at one end into pericardium at the other end to the exterior.

12. They have nervous system consisting of four pairs of ganglia  namely cerebral, pleural,pedal and visceral.

13. They have cerebral and pleural ganglia fused into a single cerebro-pleural ganglion.

14. They have statocyst and osphradia as sense organ.

15.They are unisexual or bisexual.

 

characteristics of class -SCAPHOPODA of Mollusca

The word Scaphopoda is derived from two Greek words.They are scapha=boat and podos=foot. So it includes molluscas having boat shaped body. However the characteristics can be listed as below.
1)They are exclusively marine animals.
2) They have bilaterally symmetrical, elongated body and enclosed in a tusk-like shell open at both ends.
3) They do not have eyes, tentacles and gills.
4) They have tubular Mantle completely enclosing the body.
5) They have mouth surrounded by lobular process or outgrowths.
6) They have reduced foot used for digging .
7) They have rudinmentary heart.
8) They have sexes in separate bodies.
      Example:-Dentalium 

Orders of subclass3-PULMONATA

The subclass 3-Pulmonata has only two orders namely as follows.
Order 1:-BASOMMATOPHORA
  Order 2:-STYLOMMATOPHORA


Order 1:-BASOMMATOPHORA 
          1) They are found in marine water, freshwater and brackish
              water.
          2) They have delicate shell with a conical spire and large
               aperture.
         3) They have one pair of non-invaginable tentacles with the   
          eyes at their bases.
         4) The male and female gonopores are generally separate.
               Examples:- Siphonaria, Lymnaea, Planorbis

ventral surface of Siphonaria

Siphonaria in garden

Dorsal structure of Siphonaria

                                          

planorbis

Lymnaea

Lymnaea

Order2:-STYLOMMATOPHORA
       1) They are terrestrial pulmonates.
         2) They have shell with a conical spire, internal or absent.
         3) They have two pairs of invaginable or retractile tentacles
             with the eyes at the tips of the posterior pairs.
         4) They have male and female gonopores usually united.
             Examples:- Limax, Helix, Partula, Retinella.

limax

Partula

Retinella.

              

characteristics of subclass 3-PULMONATA

1) They are mostly fresh water or terrestrial and few marine .
2) They have typical spiral shell or reduced or absent.If present 
    partly or completely concealed by mantle.
3)They donot have operculum.
4) They have mantle cavity transformed into a pulmonary sac with
   a narrow pore on the right side . Gill is absent.
5) They have heart with one auricle anterior to the ventricle.
6) They are hermaphrodite.

Characteristics of orders-9-NUDIBRANCHIA,10-RHODOPACEA,11-PYRAMIDELLACEA ,12-PARASITA of subclass OPISTHOBRANCHIA

Order 9:-NUDIBRANCHI

 1)They do not have or are naked

 2) They do not have internal gill or ctenidium an
    osphradium

 3) Mantle and mantle cavity is absent in them

 4) They respire by secondary branchiae which are usually

     arranged in circlet around the anus.


    Examples:-Doris, Tritonia, Armina, Eolis.   

Armina

 
Eolis 

Eolis

Order10:-RHODOPACEA 

  1) They are vermiform snail.

  2) They are without external appendages.

  3) They have nephridia of protonephridial type.

       Example:-Rhodope.  

Rhodope.

Order11:PYRAMIDELLACEA
  1) They have spirally twisted shell
  2) They have long invaginable proboscis.
  3) They do not have operculum.
  4) They do not have gills and radula. 
       Examples:-Turbonilla, Odostomia

Turbonilla,

Odostomia

Order12:- PARASITA

 1) They are endoparasitic gastropods found in the interior 
  of holothurians.

  2) They are extremely degenerated snails. 
Examples:-Entoconcha, Thyonicola

Entoconcha

Thyonicola

       






























   












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Characteristics of orders-6-PHILILNOGLOSSACEA,7-SACCOGLOSSA,8-NOTASPIDEA of subclass OPISTHOBRANCHIA

Order6:- PHILILNOGLOSSACEA

             1) They are minute naked snail.

         2) They do not have head appendages.

         3) They do not have gills..

           4) They have visceral mass separated from the foot   

                only by a shallow groove.

                Example:- Philinoglossa.

Philinoglossa

Order7:- SACCOGLOSSA

               1)They may be with or without shell.

             2) They have suctorial type of Pharynx.

             3) They have closed type of sperm duct.

             4) They have Parapodia and cerata.

                Example:- Oxynoe.

oxynoe

oxynoe

Order8:-NOTASPIDEA

1)They may or may not have shell.

2) They donot have Parapodia.

3) They have bipectinate gills and ospharadium on the right side.

4) They have mantle but devoid of mantle cavity.

   Examples:-Tylodina, Pleurobranchus.

Pleurobranchus.

                     















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Characteristics of orders-3-ANASPIDEA,4-PTEROPODA,5-ACOCHILIDIACEA of subclass OPISTHOBRANCHIA

Order3:- ANASPIDEA

1) They are mostly found in tropica; and subtropical 
     waters.

2) They have small shell more or less covered by 
     mantle.

3) They have well developed Parapodial lobes.

4) The anterior end of these animals bears a pair of  

     tentacles ,a pair of rhinophores and a pair eyes.

5) The sperm duct opens to the penis located    
     anteriorly after running through the body length.

     Examples:-Aplysia, Akera.

Aplysia californica

Aplysia

                 

Alkera

                    



Order4:- -PTEROPODA

1) They include Pelagic snails with or without   
    shell.

2) They swim by a pair of lateral expansions.

                            3) They are protandrous , hermaphrodite with   
                                an  open sperm  groove.

                               Examples:-Spiratella, Cavolina, Peraclis, Clione.

                          

Spiratella

Cavolina

   

            











Order5:- ACOCHILIDIACEA

     

1)They are minute without shell or naked snail.

2) They have gills ,parapodia and visceral sac  

     projecting  behind the foot.

3) They may be monoecious or dioecious.

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Characteristics of order1-ONCHIDIACEA and order2-CEPHALASPIDEA of subclass-OPISTHOBRANCHIA

Order1-ONCHIDIACEA

1) They are slug-like, naked or without shell.

2) They have mantle which is projected widely beyond  

    the foot.

3) They have head with a pair retractile tentacles each  

     tipped with an eye.

4) Pulmonary sac ,anus and female gonopore located at 

     the posterior end.

5) They have male gonpore placed posteriorly.

  Examples:-Onchidium, Onchidella.

Onchidella nigricans

Onchidella celtica

 

     

Order2-CEPHALASPIDEA 

1) They generally have shell but may be partly or wholly

    enclosed by mantle.

2) They may or maynot have Parapodial lobes.

3) They have head with tentacular shield.

Examples:-Acteon, Hydatina, Bulla

Bulla peasiana

Acteon tonatilis 

Hydatina

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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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