Phylum MolluscaGeneral Characteristics:

Molluscus, which means “soft”

General Characteristics 2nd largest animal phylum, next to

Arthropoda Are bilateral, have 3 tissue layers, and a

coelom All organ systems Have a soft body – protected by a shell in

some species

General Characteristics Have a mantle – fold of skin that surrounds

the organs. The space created inside of the fold is called the mantle cavity

Have a large ventral foot – used for location or attachment. The foot is divided into tentacles in squids and octopuses.

General Characteristics Most – but not all – mollusks have an open

circulatory system. A heart pumps blood into vessels that are open-ended. The blood flows out of the vessels and bathes the body organs.

General Characteristics Gas exchange occurs across the gills in

aquatic mollusks and across simple lungs in terrestrial mollusks.

General Characteristics Like roundworms and segmented worms, all

mollusks have a digestive tract with 2 openings and specialized regions.

Have evolved many methods of obtaining food. Most sessile and slow-moving mollusks are filter-feeders. Some mollusks, such as snails, are herbivores with special mouthparts adapted to gather vegetation or algae. Predatory mollusks, such as squids and octopuses, use their beak-like jaws to capture prey.

General Characteristics Simple nervous system with the exception of

squid and octopuses, which are capable of learning behavior and adapting their actions to locate and capture prey.

General Characteristics Most mollusks have separate sexes, and all

mollusks reproduce sexually. Reproduction can involve external fertilization, as in clams, or internal fertilization, as in squids and some snails.

General Characteristics On the basis of both internal and external

features, it would seem that mollusks and segmented worms are not at all closely related. However, comparison of larvae indicates that they probably evolved from a common ancestor.

Class Cephalopoda Octopuses, squids and nautiluses are

examples of cephalopods “Cephalo –” meaning “head”, and “poda”

meaning “footed”.

Octopus

Class Cephalopoda Zoologist think this group is the most recently evolved class

of mollusks.Cephalopods have a well-developed nervous system. Their

large brain and extensive network of nerves enable them to respond quickly and control their body motions efficiently. Octopuses are considered to be among the most intelligent invertebrates.

Unlike other mollusks, cephalopods have a closed circulatory system. This means their blood travels inside a continuous network of vessels. A closed circulatory system provides tissues with a more steady supply of oxygen and nutrients than does an open circulatory system. A closed circulatory system is associated with advanced kinds of animals.

Class Cephalopoda Cephalopods can emit a cloud of ink as a

decoy when danger threatens, and they can change color to blend in with their surroundings (cryptic coloration).

Cephalopods seize their prey (other mollusks and crustaceans) with their tentacles and paralyze it by venom produced in the salivary glands

Class CephalopodaOne way to distinguish squids from octopuses

is by the number of tentacles. Octopuses have 8, squids have 10.

Some species of squids and octopuses grow very large.

The giant squid is the world’s largest living invertebrate. The largest one measured was just over 60 feet long. Giant squids live in cold waters of the North Atlantic, where their only predators are thought to be sperm whales. Octopus Intelligence

Class Cephalopoda The only cephalopod that can be found in the

Chesapeake Bay is the Brief squid. These agile, quick swimmers grow to about 5 inches and come into the Bay from the summer to fall.

Monsterquest: Giant Squid

Class Bivalvia Clams, mussels, scallops, and oysters are

examples of bivalues. The word bivalvia comes from “bi” meaning

2 and “valvia” meaning halves. A hinge attaches the two shells of a bivalve.

Clams Mussels Scallops

Oysters

Class Bivalvia Strong muscles called adductor muscles

control the opening and closing of the hinged shells, allowing a bivalve to control the flow of water over its body.

Calcium carbonate, which is used to form the shell is secreted from the mantle.

Class Bivalvia Most bivalves inhabit marine environments. Most bivalves are filter-feeders. Food

particles in the water flowing into the body are trapped by mucus on the gills. Cilia on the gill cells pass the food along to the bivalve’s mouth.

Mouth

Gill

Class Bivalvia Various species of clams, mussels, scallops and

oysters inhabit the Chesapeake Bay. Aside from the Blue crab, if there is one Chesapeake

Bay animal that everyone recognizes immediately, it is the oyster.

Two species of oyster make their home in the Bay: the Fossil oyster and the American oyster. American oysters are the more tasty species. They live in beds (bars) mostly in mid-Bay regions in water between 8 to 25 feed deep. The locations of major oyster bars are well-know to commercial oystermen.

Class Bivalvia Zoologists identify mollusks by their shell

type (if any) and by the kind of food they eat. Of the 6 mollusk classes currently recognized, 3 contain the most familiar and numerous mollusks. They are: Class Gastropoda, Class Bivalvia and Class Cephalopoda.

Class Gastropoda Largest class of mollusks Gastropods include snails, slugs,

nudibranchs, abalones, and conches. The word gastropoda comes from “gastro” meaning stomach and “poda” meaning footed. Their foot appears to be attached to their stomach.

Class Gastropoda Nudibranchs are a large family of sea slugs.

Many of them have feathery, external gills, are poisonous, and employ warning coloration. A few species of nudibranchs and other kids of sea slugs can be found in the Chesapeake Bay.

Class Gastropoda Abalones are a family of large sea snails that

live mainly in cool to warm coastal waters. They are a favorite food of sea otters and are a delicacy among people.

Class Gastropoda Conches are another family of large sea

snails. They live mainly in tropical coastal waters, where they feed on seaweeds. Their shells have been used as money from the earliest times. They are often made into soups and other dishes.