Mollusks and Echinoderms – notes
Characteristics of Mollusks / • Soft-bodied invertebrates• Have bilateral symmetry, coelom, cephalization, true organ systems
• Usually have one or two shells with organs in a fluid filled cavity
• Most live in water
• Diverse - Many different species
• Well developed nervous system in most
4 Body Parts / 1. Foot- muscular and modified in each group: used for crawling, burrowing, or may form tentacles for capturing prey
2. Mantle (covering) – thin layer that covers most of the body and secretes the shell
3. Shell – made of calcium carbonate – for protection
4. Visceral mass – area where internal organs are located.
3 Groups of Mollusks / Classified into three common groups based on shell presence and type and foot modification
1. Gastropods
• Largest group of mollusks
• Usually have a single shell
• Use a radula (a tongue-like organ with rows of teeth) to get food
• Have foot glands that secrete a layer of mucus for sliding
• Includes snails, conchs, and garden slugs
2. Bivalves
• Have a hinged, two-part shell
• To open or close their shell they either contract or relax their muscles
• Includes clams, oysters, and scallops
• Well adapted for water
• Clams can burrow in sand
• Mussels attach themselves to a solid surface
• Scallops escape predators by rapidly opening and closing their shell
3. Cephalopods
• Most specialized and complex mollusks.
• Include squid, octopuses, and chambered nautiluses.
• Have a well developed head and many tentacles for capturing prey.
• Closed circulatory system
• Moves blood through the body in a series of closed vessels like humans.
• Use jet propulsion to move at speeds of 6 m/s.
Mollusk Body Functions / 1. Feeding – herbivores, carnivores, filter feeders, detritivores, or parasites; some use radula (tongue with teeth) to feed; filter feeders suck in water with a siphon
2. Respiration/Circulation/Excretion – advanced organ systems - aquatic mollusks have gills, terrestrial mollusks use diffusion; open circulatory system in some, closed in others
3. Response/Movement- well developed nervous system in most, use mucus to slide, foot to crawl, jet propulsion in water. Octopi are most intelligent invertebrates
4. Reproduction – sexual, internal and external fertilization, some hermaphrodites
Importance of Mollusks /
- Sources of food for humans and other animals.
- Biologists can use some mollusks to monitor water quality in an area because they concentrate dangerous chemicals in their tissues
- Some mollusks never seem to develop cancer –research being done to apply to human health care
Echinoderms / • Characteristics
– Embryonic development most similar to vertebrates
– Have a thin, bumpy or spiny epidermis
– Radial symmetrical—allowing them to sense food, predators and other things in the environment from all directions. Have no head or brain, but have a nerve ring that surrounds the mouth
– Have mouth, stomach, intestines
– Feed on a variety of plants and animals
– Also have cells that respond to light and touch
Echinoderms’ Water Vascular System / • A characteristic unique to echinoderms
• Allows them to move, exchange CO2 and O2, capture food, and release wastes
• It is a network of water-filled canals with thousands of tube feet connected to it.
• Tube feet—hollow, thin walled tubes that ends in a suction cup.
– As pressure in the tube feet changes the animal is able to move along by pushing out and pulling in its tube feet
Types of Echinoderms / • Sea Stars
• Brittle Stars
• Sea Urchins
• Sand Dollars
• Sea Cucumbers