Marveling at Mollusks

Linnaen System of Classification

Phylum Mollusca Molluscus means soft bodied.Molluscus means soft bodied. Second largest phyllum aside from arthropodaSecond largest phyllum aside from arthropoda Mollusks include clams, snails, slugs, nautiluses, cuttlefish, octopuses, and squid.Mollusks include clams, snails, slugs, nautiluses, cuttlefish, octopuses, and squid. Most have an external or internal shellMost have an external or internal shell Some are quite intelligent (some species of Octopus actually play and learn!)Some are quite intelligent (some species of Octopus actually play and learn!) Many mollusks are characterized by a rasping feeding organ called a radula, which has teeth for scraping food and drilling into shells of other organisms.Many mollusks are characterized by a rasping feeding organ called a radula, which has teeth for scraping food and drilling into shells of other organisms.

Where they live Occupy a wide range of habitats including:Occupy a wide range of habitats including: Abyssal plainsAbyssal plains Continental ShelvesContinental Shelves Intertidal mudflatsIntertidal mudflats

Body Structure Bilaterally symmetricalBilaterally symmetrical Flow through digestive tractsFlow through digestive tracts Well developed nervous systemsWell developed nervous systems A few are segmentedA few are segmented Can secrete their own shells usually made of calcite or aragoniteCan secrete their own shells usually made of calcite or aragonite

3 classes GastropodaGastropoda BivalviaBivalvia CephalopodaCephalopoda

Gastropods SnailsSnails Gaster means stomach, pod means foot.Gaster means stomach, pod means foot. Include abalone, conch, and common garden snailInclude abalone, conch, and common garden snail Some are grazers, some are suspension feeders, and some are predators.Some are grazers, some are suspension feeders, and some are predators. Pteropods and Heteropods are planktonic gastropodsPteropods and Heteropods are planktonic gastropods Benthic: Most marine gastropods are found on rocky bottoms or firm substratesBenthic: Most marine gastropods are found on rocky bottoms or firm substrates

Gastropods Gastropods build their own shells which it enlarges and adds to as it grows.Gastropods build their own shells which it enlarges and adds to as it grows. Shell is often coiled for easier movementShell is often coiled for easier movement Foot and head protrude from the shellFoot and head protrude from the shell Shell has 3 layersShell has 3 layers A fibrous outer covering to distribute shockA fibrous outer covering to distribute shock A strong, crystalline layer of calcite to provide strengthA strong, crystalline layer of calcite to provide strength An inner layer of smooth calcite to provide nonabrasive surroundings for the snail. Wouldn’t want to get scratched.An inner layer of smooth calcite to provide nonabrasive surroundings for the snail. Wouldn’t want to get scratched. Sea slugs are gastropods without shells.Sea slugs are gastropods without shells.

What’s that foot for? Mostly for moving about slowly, but sometimes used for burrowing.Mostly for moving about slowly, but sometimes used for burrowing.

Gastropod Morphology Shells characterized by torsion, where the respiratory organs are above the head.Shells characterized by torsion, where the respiratory organs are above the head. Allows for the withdrawal of head before the foot into the shell.Allows for the withdrawal of head before the foot into the shell. Foot has a hard part called the operculum to protect the snail inside the shell.Foot has a hard part called the operculum to protect the snail inside the shell. Shell made of aragonite or calcite. Usually conical with spirals called whorls. Has an opening called an apertureShell made of aragonite or calcite. Usually conical with spirals called whorls. Has an opening called an aperture

Bivalves Bi means two, valve means door.Bi means two, valve means door. Includes clams, oysters, mussels, and scallopsIncludes clams, oysters, mussels, and scallops Surrendered mobility for protection, though some scallops can swim by pushing their valves open and closed quickly.Surrendered mobility for protection, though some scallops can swim by pushing their valves open and closed quickly. Eat by suspension feeding (filter feeding).Eat by suspension feeding (filter feeding). Benthic organismsBenthic organisms Infaunal and Epifaunal speciesInfaunal and Epifaunal species Infaunal: Burrows into sedimentInfaunal: Burrows into sediment Epifaunal: Lives on top of sediment or attaches to rocks.Epifaunal: Lives on top of sediment or attaches to rocks.

Infaunal BIvalves Use their foot to burrow into soft sediment on ocean floor.Use their foot to burrow into soft sediment on ocean floor. Have a siphon that sticks up through sediment to obtain water and eject wastes.Have a siphon that sticks up through sediment to obtain water and eject wastes. Many clams do this.Many clams do this.