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PHYLUM MOLLUSCA (Molle= soft body). PHYLUM MOLLUSCA OVER 100,OOO LIVING SPECIES; MANY 1000’S OF FOSSIL SPECIES FOUND IN ALMOST ALL ENVIRONMENTS: MARINE,

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Presentation on theme: "PHYLUM MOLLUSCA (Molle= soft body). PHYLUM MOLLUSCA OVER 100,OOO LIVING SPECIES; MANY 1000’S OF FOSSIL SPECIES FOUND IN ALMOST ALL ENVIRONMENTS: MARINE,"— Presentation transcript:

1 PHYLUM MOLLUSCA (Molle= soft body)

2 PHYLUM MOLLUSCA OVER 100,OOO LIVING SPECIES; MANY 1000’S OF FOSSIL SPECIES FOUND IN ALMOST ALL ENVIRONMENTS: MARINE, FRESHWATER, TERRESTRIAL INCLUDES SNAILS, SLUGS, CLAMS, SQUIDS, OCTOPUSES,

3 CHARACTERISTICS Body Plan: three main parts- head, foot, visceral mass body is unsegmented

4 Mantle - specialized tissue, secretes shell, may be involved in feeding, reproduction and respiration Radula – for rasping; in all but one class CHARACTERISTICS Radula closeup

5 ALL ORGAN SYSTEMS ARE PRESENT Circulation - Open (Hemocoel) - Hemocyanin Respiratory System - gills (Ctenidia), lungs, mantle, epidermis Osmoregulation - Metanephridia also excretion

6 Feeding - Radula (scraping) –Bivalves - Filter feed Nervous System - Complex system of Ganglia ALL ORGAN SYSTEMS ARE PRESENT

7 Reproductive System - usually dioecious, monoecious in some –Marine forms have free living trochophore larva –Other larval stages may be present ALL ORGAN SYSTEMS ARE PRESENT

8 MOLLUSCAN CLASSES

9 Class Monoplacophora “one plate ” all known from deep marine waters (>12,000 feet) have a single circular shell with radula

10 Class Polyplacophora “many plates”- (chitons) have 8 overlapping plates or shells –reduced head, no eyes or tentacles –all marine; usually live on rocky shores –have radula, gills –external fertilization –scrape algae

11 Polyplacophora Respiration - Gills in pallial groove Circulation - Heart at posterior end - single Aorta Excretion - Nephridia Nervous System and sense organs - Ganglia and nerves –Sub Radular organ - Feeding –Esthetes - light sensing –Osphradia - Sampling water

12 Polyplacophora Reproduction - Sexes Separate –Usually external fertilization –Trochophore larva

13 Class Aplacophora “without plates ” Rare; lack shell; wormlike deep marine; burrowing species; predators About 320 species, not much is known of them Your book separates them into two separate classes: –!Caudofoveata –!Solenogastres

14 Class Gastropoda Largest class of Molluscs Most important feature is Torsion

15 Torsion Twisting of body into loop Perhaps adaptation of veliger larva Disadvantages: –Reduction of organs on right side –Excretion - Mouth moves near anus Adavntages –Allows water to be drawn from the front

16 Gastropod - Locomotion Foot Ciliary action below the foot Operculum Swimming

17 Gastropod - Nutrition Herbivores - Radula Carnivores Filter feeders NERVOUS SYSTEM –Similar to Chiton - but in the shape of “8”

18 Class - Bivalvia Includes Calms, Oysters, Mussels Has two Shells (Valves) Shell held together by Adductor muscle Head is lost Filter feeders Mantle secretes the shell

19 MOLLUSCAN SHELL STRUCTURE Periostracum ; outer layer Prismatic; middle layer Nacre; inside layer- mother of pearl

20 BIVALVIA Locomotion –Foot (burrowers) –Active swimmers (Scallops) Circulation –Open system Excretion –Nephridia

21 BIVALVIA Nervous System –2 pairs of ganglia –Sense organs (statocysts, ocelli, ospharidia) Reproduction –Sexes separate –Internal fertilization –Larva - Glochidium

22 Class - Cephalopoda Includes Squid, octopus, Nautilus Most advanced of Molluscs Well developed head and eyes Head has tentacles with suckers Squids are largest of invertebrates Locomotion by jet propulsion

23 Class Scaphopoda (tusk shells) slender, tubular shells open at both ends all marine have tentacles around mouth no defined head no gills, respiration across mantle


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