Phylum Mollusca
General Characteristics
• Marine, freshwater, terrestrial
• 100,000 named species
• Snails, oysters, octupi are examples
• Coelomate
• Bilateral symmetry
• Body divided into 4 distinct parts: foot, head, visceral mass, shell
• Trochopore larva- larva never leaves egg
Kingdom AnimaliaPhylum MolluscaClass Bivalvia
Structures
• head-foot contains mouth and other sensory organs
foot is the large muscular organ used for locomotion
• Visceral mass- contains the heart and other major organs
• Mantle- epidermis of bivalve-secretes shell
• Mantle cavity- space between mantle and visceral mass
• Gills- located in mantle cavity- gas exchange
• Ganglia- located in visceral mass – brain
• Radula-flexible, tongue like strip of tissue covered with teeth that point backward
Organ Systems
• Circulatory System: 3 chambered heart
• Open circulatory system- blood leaks out of blood vessels and bathes the body tissue directly
• 2 chambers of heart collect blood from gills
• 3rd heart chamber, pumps oxygenated blood out of vessels and into spaces in tissue
• Blood returns to heart by gills
• Blood has an oxygen carrying molecule called hemoglobin
• Blood is blue in color
Bivalve: Respiratory
• Breathe with ciliated gills located in mantle cavity
• Mantle cavity- space between mantle and visceral mass
• Constant beating of gills causes a continuous stream of water to pass over the gills
• Gills are very efficient
Excretory System
• The coelom is used as a cavity in which waste filled body fluids are collected
• Nephridia- structured that filter waste
Reproductive System
• Sexual
• External fertilization- eggs and sperm are released into water. The eggs are fertilized and turn into tiny free swimming larva called trochophores.
• The larvae settle and then grow into mature adults
Locomotion
• foot
Kingdom AnimaliaPhylum MolluscaClass Gastropoda
Structures
• Shell- growth of shell is not regular and even and is influenced by a variety of factors including growth hormones, food and temp.
• Foot- locomotion -mucus is secreted and the snail moves over mucus
• Oesophagus- food tube
• Crop- storage organ
• Stomach – digests food
• Intestine- absorbs nutrients
Digestive system
• Mouth- oesophagus- crop-stomach- intestine and anus
Circulatory system
• Open circulatory system
• 2 chambered Heart- thick outer surface(pericardium), ventricle and atrium(auricle)
Respiratory System
• Terrestrial – modified Lungs out of mantle cavities
• Aquatic- gills
Nervous system
• Brain
• Eyes
• organs of taste, smell and equilibrium
• More evolved nerve net connected to brain
Reproduction
Aquatic snails are mostly separate sexes with cross fertilization
Terrestrial snails- hermaphroditic
Internal fertilization
Kingdom AnimaliaPhylum MolluscaClass CephalopodaRepresentative: squid
Structures
• 10 arms 2 are Tentacles which are used for feeding
• Radula- some have these-used a tongue to direct food
• Water jet- propulsion
• Ink sac-used for defense/ camoflage
• Intestine – absorbs nutrients
• Kidney- collects urea from blood
• Stomach- digestive organ
• Heart- circulates blood
• pen
Digestive System
• Carnivorous
• Tentacles- grab food
• Horny beak(jaws)- grasp and shred food
• Radula- pushes food into throat
• Salivary glands- begins digestion
• Esophagus- food tube- connects throat with stomach
• Liver/pancreas act together- produces digestive enzymes
• Stomach- digestion truly begins here
• Intestine- absorbs nutrients
• Anus- excretes waste
Respiratory System
• Gills
Circulatory System
• 3 hearts- 1 heart at the base of each gill these are called the gill or brachial hearts. Another heart called the systemic heart serves the mantle and internal organs( found slightly below the brachial hearts)
Nervous System
• Most advanced brain in invertebrates
• 80% of brain activity is used for visual activities which then aids swimming
• Some octopus have been able to learn much like rats
• 2 large eyes- binocular vision
• Can detect smells
• Can produce sound and respond to sound( not through ear as such but statocysts, which help maintain balance as well
• Have sense of taste and touch
Reproductive System
• Sexual
• Separate sexes
• Can be internal or external fertilization
Excretory System
• Kidney
• anus