PHYLUM MOLLUSCA Class Bivalvia 1 Clams oysters mussels
PHYLUM MOLLUSCA
Class Bivalvia 1. Clams, oysters, mussels, scallops. 2. All marine or freshwater 3. Second largest class 4. All have 2 shells
A. Locomotion 1. Clams/mussels- muscular foot for burrowing 2. Oysters- adults are sessile 3. Scallops- “clap” shell
B. Shell Features Prismatic 1. Shell structure a. Periostracum- thin outer layer of protein b. Prismatic layer- thick middle layer of calcium carbonate c. Nacreous layer- inner layer; secretes nacre which forms pearls in some. Nacreous Periostracum
3. Umbo- swollen area near anterior, dorsal end of clam; oldest part of shell. 4. Hinge ligament- holds two shells together 5. Growth lines- wider lines indicate more growth/better feeding season. 6. Anterior and Posterior adductor muscles- very strong muscles for opening or closing shell.
C. Digestion/Feeding 1. Filter feeders- algae, larvae, small particles 2. Food/water enter incurrent siphon. 3. Food swept into mouth by 2 pairs of palps 4. Esophagus, stomach, intestine, anus 5. feces/excess water leave thru excurrent siphon.
D. Respiration 1. Oxygenated water enters incurrent siphon. 2. Gills have tubes where water & blood are close together. Gases exchange by diffusion across the membrane. 3. Deoxygenated water leaves thru excurrent siphon.
E. Circulation 1. Open 2. Heart and short vessels similar to gastropods.
F. Excretion 1. Nephridium G. Nervous/Sensory System 1. Ganglia concentrated in foot, esophagus, adductor muscle and mantle. 2. Some have eyes for sensing light around shell rim. 3. Osphradia- chemoreceptors
H. Reproduction 1. Most are dioeciousexternal fertilization 2. Sperm leave thru excurrent siphon 3. Sperm brought in thru incurrent siphon of female. 4. Clams release trochophore larvae which develop into adults.
5. Mussels release glochidia which look like miniature adults. • These are usually parasitic on fish. • Attach to fish gills & feed on blood. • When adult organs form, they drop off & take on filter feeding life style.
I. Economic/Environmental Significance 1. Source of food/part of food chain 2. Filter/clean water of harmful pollutants (algae)can cause sickness if red tide algae are eaten. 3. Form pearls/jewelry 4. Mother of pearl buttons made from shells
Class Cephalopoda 1. Squid, octopus, nautilus, cuttlefish 2. All marine 3. Most complex mollusk 4. No external shell, have internal support a. Squid- have internal chitinous structure called pen
b. Cuttlefish- have cuttlebone. Can be used as calcium supplement for birds. c. Chambered nautilushas true shell
d. Octopus- has no shell
Dorsal Ventral Anterior View A. Fin B. Mantle C. Chromatophores D. Water Jet E. Eye F. Arm G. Tentacle H. suckers
A. Locomotion 1. All cephalopods can move by jet propulsion- forcefully expelling water from siphons on head. 2. Octopus crawl with arms. 3. Squid & cuttlefish have posterior fins for steering/movement.
B. Digestion/Feeding 1. Have arms with suction cups to capture/hold prey. 2. Sharp beak for tearing into prey. 3. Radula for drilling holes in shells. 4. Use extracellular digestion- secrete enzymes that breaks down food before enters mouth. 5. mouth, esophagus, stomach (cecum = digestive gland), intestine, anus, siphon 6. Most nocturnal- eat Radula crustaceans, fish, other mollusks, etc. Beak
Holes created by octopus radula. “b” indicates where octopus gave up and used beak to break into shell.
C. Respiratory System 1. Gills in mantle cavity D. Circulatory System 1. Closed- blood enclosed in blood vessels. 2. Have hemocyanin- copper rich blood (blue) E. Excretory system 1. Nephridia
F. Nervous/Sensory System 1. Large brains- good memory, can work thru problems. 2. Complex eye- very similar to human eye. Can form images and distinguish color
3. Camouflage a. Chromatophores- pigments cells in skin which allow color change. Can also use to communicate with other cephalopods (mating, aggression, fear, etc) b. Suckers on arms are very sensitive. Can change texture of skin to match rocks.
4. Ink gland • ejects ink cloud when disturbed to make quick getaway. • tyrosinase- also released to irritate predators eyes and paralyze sense of smell
G. Reproduction 1. Dioecious 2. Eggs are deposited in string-like masses in octopus den. 3. Octopus brood young until they hatch. Keeping clean of debris. 4. Young never cared for after hatching.
A. Cecum B. Fin C. Testis D. Vena Cava E. Branchial heart F. Gill G. Ink sac H. Funnel I. Tentacle J. Arms K. Eye L. Intestine M. Penis N. mantle
H. Economic/Environmental Significance 1. Food source- calamari, octopus 2. Bait for commercial fishermen 3. Can be pests in oyster beds- eating up all profit! 4. Cephalotoxin may be used for medicine/research
• The Giant Squid • 50 feet long & weigh almost 1 ton • Eats fish & other squid and has been known to eat sperm whale calves
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