Download Phylum Mollusca

General 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 Cephalopoda
One 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.
Gill
Mouth
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.