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Phylum Mollusca Chapter 12

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Presentation on theme: "Phylum Mollusca Chapter 12"— Presentation transcript:

1 Phylum Mollusca Chapter 12

2 Phylum Mollusca “soft”
Three Main Classes Class Gastropoda (snails, slugs, limpets) Class Bivalvia (muscles, clams, oysters) Class Cephalopoda (octopus, squid, nautilus, cuttlefish) Limpets

3 Body Form Bilateral Symmetry Invertebrate - no backbone
Hydrostatic Skeleton (fluid under pressure) Triploblastic Coelomate 1st animals to posses a coelom Yes, even before annelids… Small cavity; surrounds heart, nephridia, gonads Protostomate Blastopore become mouth – ‘primitive’

4 Functions of the Coelom
Provides room for organ development Surface diffusion of Gases Nutrients Wastes Storage Elimination of reproductive products Hydrostatic support

5 Characteristics of Molluscs
Size: <1cm – 18m Garden slug – Giant squid 3 Body Regions Mantle – tissue that covers the body May secret a shell Fxn: excretion, gas exchange, elimination of wastes, reproductive products Visceral mass – contains organs Head foot – elongate foot w/ anterior head

6 Characteristics of Molluscs (cont.)
Open circulatory system in all except cephalopods Radula – rasping/scraping structure Covers tonguelike structure

7 Class Gastropoda Snails, limpets, slugs
Over 35,000 species <Largest class> Habitat: Marine, freshwater, terrestrial Operculum ‘lid’ Dorsal posterior end Used for protection from predators & desiccation 6th Hr Left off Here 3/7/14

8 Class Gastropoda Undergo Torsion during larval stage-
180° Twist of visceral mass & mantle Allows head to enter shell first for protection Allows for clean water in front of the snail to enter mantle cavity Makes snail more sensitive to stimuli coming from the direction in which it moves

9 Class Gastropoda Locomotion Flattened foot Cilia over mucous trail
Sometimes ciliated Muscular contractions Cilia over mucous trail

10 Class Gastropoda Nervous Communication Ospharidia
Chemoreceptors Detect sediment & chemicals in inhalant H20 Helps detect prey Ganglia linked by nerves base or end of tentacles Photo receptors Lens & Cornea Statocysts in the foot (balance) 5th Hr. Left off Here 3/7/14

11 Class Gastropoda Cardiovascular: Respiration Open Circulatory System
Blood “hemolymph” leaves blood vessels Blood bathes tissue directly in hemocoel ‘sinus’ Function of blood: transport nutrients, wastes, & gasses Respiration Gills Diffusion of O2 across mantle

12 Class Gastropoda Digestion Food trapped in mucus strings
Gets incorporated into protostyle Protostyle – rotating ‘mucoid mass’ in gut of gastropod Radula Ciliated digestive tract 2nd Hour Left off Here

13 Class Gastropoda Excretory Waste Removal
Wastes excreted through coelom from blood Aquatic – produce ammonia Terrestrial – produce uric acid (less toxic) – conserves water Nepheridium – excretory organ

14 Class Gastropoda Reproduction Marine snails – external fertilization
Dioecious Gametes discharged into sea Freshwater & Terrestrial snails – internal fertilization Monecious Copulation - Exchange sperm – or - One snail may act as the male, the other as the female

15 Class Bivalvia “two-leaf”
Mussels, clams, oysters, scallops Habitat: Marine, freshwater Help remove bacteria from polluted water 2 convex halves- valves Proteinaceous hinge

16 Class Bivalvia Tongue & grooves in shell to prevent twisting
Umbo – swollen area – looks like a notch Oldest part of shell Sheet like mantle

17 Class Bivalvia Muscular movement: Adductor muscles to close shell
Defense against predation Sea stars can break this muscle Steaming bivalves… Sessile (immobile)

18 Class Bivalvia Nervous Communication 3 pairs of interconnected ganglia
Margin of the mantle is main sense organ has sensory cells Tentacles Photo receptors or Lens & Cornea Statocysts – balance/gravity Osphraidium – chemoreceptors in mantle

19 Class Bivalvia Cardiovascular System Respiration
Open circulatory system Blood flow: heart  tissue sinuses  nepheridia  gills  heart Respiration Gills covered in cillia diffusion

20 Class Bivalvia Digestive System Filter feeders
Gills trap food particles Move down food grooves (ciliated tracts) Labial palps sort food particles

21 Class Bivalvia Excretory System 2 Nepheridia Duct system
Nephridiopores in anterior region for excretion of wastes

22 Class Bivalvia Reproduction Most dioecious – male/female
Few monoecous – hermaphroditic Most external fertilization Spew out gametes and fertilize in sea Some internal fertilization (fresh water only) Female sucks in sperm from inhalent water Young clams shed from gills

23 Class Cephalopoda

24 Class Cephalopoda “head foot”
Most complex mollusc All except nautilus have a reduced shell Cuttlefish & squid have internal shell Nautilus has a coiled shell for support Modified foot for food capture, attachment, locomotion, & reproduction Visceral mass located in head segment

25 Class Cephalopoda Muscular movement Jet propulsion
Foot modified into tentacles

26 Class Cephalopoda Nervous Communication
Highly developed nervous system Brains are large Fusion of ganglia Statocysts (gravity) Eyes

27 Class Cephalopoda Cardiovascular 1st to have Closed circulatory system
Heart consists of 2 auricles and 1 ventricle Have contractile arteries and branchial hearts Respiration Gills & diffusion

28 Class Cephalopoda Digestive System Jaws & Radula
Tentacles w/ adhesive cups or foot to capture prey Feed on small invertebrates Efficient predators

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