Mollusks

How can cephalopods protect themselves against predators?

Color changes effected by chromatophores (pigment cells) Allows them to blend into their background Squirting out water by jet propulsion helps escape predators Squids also release an inky substance into the water

Describe at least one important use of Mollusks for humans.

As food - mussels, clams, oysters, abalone, calamari (squid), octopus, escargot (snails), etc. For Adornment - Pearls - formed in oysters and clams. Shiny inner layer of some shells used to make buttons.

Class Gastropoda

Gastropoda is the largest of the mollusk classes. 70,000 named species. Include snails, slugs, sea hares, sea slugs, sea butterflies. Marine, freshwater, terrestrial. Slugs lack a shell! The shell of a gastropod is always one piece - univalve - and may be coiled or uncoiled. The apex contains the oldest and smallest whorl. Shells may coil to the right or left - this is genetically controlled.

trochophore

free-swimming larval stage

Bivalve Respiration occurs how?

gills and filter feeding

Class Bivalves

Bivalve mollusks have two shells (valves). Mussels, clams, oysters, scallops, shipworms. Mostly sessile filter feeders. No head or radula Laterally (right-left) compressed shell Shells are held together by a hinge ligament Umbo is the oldest part of the shell Growth occurs in concentric rings around it

How do Bivalves move?

Bivalves move around by extending the muscular foot between the shells. Scallops and file shells swim by clapping their shells together to create jet propulsion.

Class Cephalopoda

Cephalopods include octopuses, squid, nautiluses and cuttlefish. Marine carnivores with beak-like jaws Surrounded by tentacles modified from their foot. Shells of the Nautilus are made buoyant by a series of gas chambers. Most cephalopods have complex eyes with cornea, lens, chambers, and retina. Largest invertebrate brain Closed circulation

How do cephalopods move?

Cephalopods swim by expelling water from the mantle cavity through a ventral funnel.

Lobe Finned:

Fins are long, fleshy, muscular, supported by central core of bones. Thought to be ancestors of amphibians. Examples are: Coelacanth, Lungfish

What are incurrent and excurrent siphons used for?

Gas exchange Filter feeding Jet propulsion

radula

Have a scraping, mouth-like structure

Give 3 examples of animals that belong to the phylum mollusca

Includes snails and slugs, oysters and clams, and octopuses and squids

Class Polyplacophora

Includes the chitons Eight overlapping plates Can roll up Live mostly in the rocky intertidal zones. Use radula to scrape algae off rocks. Water flows over gills to respire

Class Scaphopoda

Includes the tusk shells. Found in subtidal zone to 6000 m deep. Mantle wraps around visceral mass and is fused, forming a tube.

How do cephalopods differ from other mollusks?

Many mollusks have an open circulatory system with a pumping heart, blood vessels and blood sinuses. Most cephalopods (squid & octopus) have a closed circulatory system with a heart, blood vessels and capillaries.

What feature can snails use to defend themselves from predators?

Many snails can withdraw into the shell and close it off with a horny operculum

Where can Mollusks be found?

Mollusks can be found as marine (ocean) , freshwater ( Rivers, lakes and streams) or terrestrial (land) life

Cephallopoda Reproduction

Sexes are separate in cephalopods. Juveniles hatch directly from eggs - no free-swimming larvae. One arm of male removes a spermatophore from mantle cavity and inserts it into female.

Choose one type of mollusk and describe how it can be considered a pest

Shipworms - burrow through wood, including docks & ships. Terrestrial snails and slugs damage garden plants. Mollusks serve as an intermediate host for many parasites. Zebra mussels - accidentally introduced into the Great Lakes and reeking havoc with the ecosystem

Describe the basic structure of a mollusk (3 main parts)

The 3 main parts of a mollusk include the muscular foot for movement, visceral mass (main organs) and mantle (shell like structure that develops over time)

Visceral mass

containing digestive, circulatory, respiratory and reproductive organs

Cephalization

have a distinct head with sense organs & brain

Mantle

houses the gills and in some secretes a protective shell over the visceral mass.

dioecious

separate sexes