PHYLUM MOLLUSCA
HISTORY
Phylum Mollusca are successfully living since Cambrian time. Presently 500,000 living species besides fossils. For the first time molluscs have acquired hard shell for protection. They are all free-living in fresh water, brackish water and sea water. Clams, oysters, squids serve as human food. Pearl oysters produce pearls for human ornaments. Certain snails serve as intermediate host for helminthic diseases of man and his animals. Gastropod molluscs reveal torsion and detortion. Phylum mollusca have medical importance. Pila globosa is the slowest moving animal.
DIAGNOSTIC CHARACTERS OF PHYLUM MOLLUSCA
- Unsegmented (except in Monoplacophora).
- Presence of shell mantle, visceral mass and foot.
- Circulatory system open.
- Excretion by paired metanephridia.
CLASSIFICATION OF PHYLUM MOLLUSCA

CLASS I AMPHINEURA
- Elongated or oval body.
- Head reduced without eyes and tentacles.
Order 1 Aplacophora
- Worm like without shell and foot.
- Integument thick with minute spicules.
Example :- Chaetoderma
Order 2 Polyplacophora
- Body oval with large flat foot.
- Shell of a midorsal row of 8 broad plates.
Example :- Chiton, lschnochiton
CLASS II SCAPHOPODA
- Tooth shells or tusk shells.
- Shell and mantle tubular, curved and open at both ends.
Example :- Dentalium
CLASS III GASTROPODA
- Univalve shell usually spirally coiled due to torsion.
- Tentacles and eyes present.
SUB-CLASS (A) PROSOBRANCHIATA (= STREPTONEURA)
- Nervous system in the form of 8.
- Gills (Ctenidia) anterior to heart.
Order 1 Aspidobranchiata
- Two rows of mamentous gills.
- Two auricles, two nephridia.
Sub-order 1 Docoglassa
- Nervous system less concentrated.
- Ctenidium replaced by secondary gills.
Example :- Patella, Acmea, Lottia.
Sub–order 2 Rhipidoglossa
- Shell valves without insertion plates.
- Few Ctenidia
Example :- Lepidioplurus, Haliotes Trochus, Turbo.
Order 2 Pectinibranchiata
- Nervous system not concentrated.
- Single ctenidium.
Sub-order 1 Taenioglossa
Sub–order 2 Rachiglossa
- Nervous system concentrated.
- Edge of shell with siphonal notch or canal.
Example :- Buccinium, Murex, Conus
SUB-CLASS (B) EUTHYNEURA
- Shell reduced.
- Nerves not twisted in the form of 8.
Order 1 Opisthobranchia
- Viscera and nervous system secondarily unwound.
- Single nephridium, auricle and gill.
Sub-order 1 Tectibranchia
- Shell internal, single gill.
- Parapodial lobes large.
Example :- Aplysia, Bulla.
Sub–order 2 pteropoda
- Shell present.
- Foot modified into wing like parapodia for swimming.
Example :- Cavolina.
Sub–order 3 Nudibranchia
Order 2 Pulmonata
- Fresh-water and land snails and slugs.
- Shell a simple spire or absent.
Sub-order 1 Basommatophora
Sub–order 2 Stylommatophora
CLASS IV BIVALVIA OR PELECYPODA
- Bivalve shell made of 2 lateral valves.
- Mantle flattened gills 1 or 2 pairs.
Order 1 Protobranchiata
- Gill with central axis bearing 2 divergent rows of short filaments.
- Foot flat ventrally. Two adductor muscles.
Example :- Solenomya, Leda.
Order 2 Fillibranchiata or Lamellibranchiata
- Gills enlarged. filliform.
- Often with byssus.
Example :- Mytilus. Arca.
Order 3 Pseudolamellibranchiata
- . Gills from vertical folds.
- Anterior adductor muscle large. Siphon absent.
Example :- Pecten. Oyster. Pearl oyster.
Order 4 Eulamellibranchiata
CLASS V CEPHALOPODA
- Head large, eyes conspicuous and complex.
- Shell external or internal or absent
SUB-CLASS A DIBRANCHIATA
SUB-CLASS B TETRABRANCHIATA
SUB-CLASS C AMMONODIA
- Shell external
- Suturelines irregular
Example :- Ammonites.
OUR POSTS
SPHENODON : TUATARA
SPHENODON : TUATARA CLASSIFICATION OF SPHENODON : TUATARA PHYLUM :- CHORDATA (Notochord, dorsal tubular nerve cord present and gill slits present ) Group :- CRANIATA ( Definite head. Cranium with ...READ MOREPASSER DOMESTICUS : SPARROW
PASSER DOMESTICUS : SPARROW CLASSIFICATION OF PASSER DOMESTICUS : SPARROW PHYLUM :- CHORDATA (Notochord, dorsal tubular nerve cord present and gill slits present ) Group :- CRANIATA ( Definite head. ...READ MOREOPHIOCEPHALUS PUNCTATUS : SNAKE HEAD
OPHIOCEPHALUS PUNCTATUS : SNAKE HEAD CLASSIFICATION OF OPHIOCEPHALUS PUNCTATUS : SNAKE HEAD Phylum :- CHORDATA ( Notochord and dorsal tubular nerve cord present and gill-slits present). Group :- ...READ MOREACIPENSER : STURGEON
ACIPENSER : STURGEON CLASSIFICATION OF ACIPENSER : STURGEON Phylum :- CHORDATA ( Notochord and dorsal tubular nerve cord present and gill-slits present). Group :- CRANIATA ( Cranium with brain ...READ MOREPOLYODON : PADDLE FISH
POLYODON : PADDLE FISH CLASSIFICATION OF POLYODON : PADDLE FISH Phylum :- CHORDATA ( Notochord and dorsal tubular nerve cord present and gill-slits present). Group :- CRANIATA ( Cranium with brain ...READ MOREMYSTUS SEENGHALA
MYSTUS SEENGHALA CLASSIFICATION OF MYSTUS SEENGHALA Phylum :- CHORDATA ( Notochord and dorsal tubular nerve cord present and gill-slits present). Group :- CRANIATA ( Cranium with brain present ). ...READ MOREDIODON : PORCUPINE FISH
DIODON : PORCUPINE FISH CLASSIFICATION OF DIODON : PORCUPINE FISH Phylum :- CHORDATA ( Notochord and dorsal tubular nerve cord present and gill-slits present). Group :- CRANIATA ( Cranium with ...READ MORESTEGOSTOMA : TIGER SHARK
STEGOSTOMA : TIGER SHARK CLASSIFICATION of STEGOSTOMA Phylum :- CHORDATA ( Notochord and dorsal tubular nerve cord present and gill-slits present). Group :- CRANIATA ( Cranium with brain present ). ...READ MOREANGUILLA VULGARIS : EEL
ANGUILLA VULGARIS : EEL CLASSIFICATION OF ANGUILLA VULGARIS : EEL Phylum :- CHORDATA ( Notochord and dorsal tubular nerve cord present and gill-slits present). Group :- CRANIATA ( Cranium with brain ...READ MOREWildLife and it’s Importance
WildLife and it’s Importance ‘Wild animal’ means any non-domesticated animal found wild in nature. It includes both vertebrates (fish, amphibians, reptiles, birds and mammals) and ...READ MORE
- Click to share on WhatsApp (Opens in new window)
- Click to share on Twitter (Opens in new window)
- Click to share on Facebook (Opens in new window)
- Click to share on LinkedIn (Opens in new window)
- Click to share on Pinterest (Opens in new window)
- Click to share on Telegram (Opens in new window)
- Click to print (Opens in new window)
- Click to share on Reddit (Opens in new window)
- Click to share on Tumblr (Opens in new window)
- Click to share on Pocket (Opens in new window)
- Click to share on Skype (Opens in new window)
Pingback: ENTOPROCTA - STRUCTURE, LIFE HISTORY AND AFFNITIES | ZOOLOGYTALKS | 2021
Pingback: ORGANIZATION OF COELOM | Zoologytalks | 2021