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Zoology Ch. 12 Molluscan Success
Molluscs are _________________ and they possess a _____________. Molluscs are _____________. Theories regarding the
_____________ of the coelom influence how zoologists interpret evolutionary ______________________ among triplobalstic
animals. Molluscs range in size and body form from the giant ____________, measuring _______m in length, to the smallest
garden _________, less than _________cm. Characteristics of the phylum Mollusca include: 1. Body of _________ parts, head
and _________ 2. _____________ that secretes a calcareous shell and covers the _______________ mass 3. Mantle cavity
functions in ______________, gas exchange, elimination of digestive wastes, and release of __________________ products 4.
_________________ symmetry. 5. Protostome characteristics, including trocophore larvae, ___________ cleavage, and
schizocoelous coelom formation 6. Coelom _______________ to cavities surrounding the ____________, nephridia, and
gonads 7. __________ circulatory system in all but one class (Cephalopoda) 8. _____________ usually present and used in
scraping food. The body of the mollusk has __________ main regions – the head-foot, the visceral mass, and the
___________.
The head-foot is elongate with an _____________ head, containing the ___________ and certain nervous and sensory
structures, and an elongate foot, used for _____________________ and __________________. The visceral mass contains the
organs of _______________, circulation, reproduction, and ______________ and is positioned ____________ to the headfoot. The mantle usually attaches to the ___________ mass, enfolds most of the body, and may secrete a ____________ that
overlies the mantle. The shell of a mollusk is secreted in ____________ layers. The ____________ layer of the shell is called
the ________________. Mantle cells at the mantle’s outer margin secrete this ________________ layer. The middle layer of
the shell, called the ________________ layer, is the _______________ of the three layers and consists of calcium carbonate.
The inner layer of the shell, the _______________ layer, forms from thin sheets of calcium carbonate. Cells along the entire
________________ border of the mantle secrete the nacreous layer. The nacre secretion ____________ the shell. Between the
mantle and the foot is a space called the ______________ _______________. The mantle cavity opens to the outside and
functions in _________ exchange, excretion, elimination of digestive wastes, and release of ________________ products. The
mouth of most mollusks possess a rasping structure called a ______________, which consists of a ______________ belt and
rows of posteriorly curved ____________. The radula overlies a fleshy tonguelike structure supported by a cartilaginous
__________________. Muscles of the odontophore permit the ____________ to be protruded from the __________, move
back and forth, and ___________ is scraped from a substrate and passed to the ______________ tract.
Class Gastropoda
The class Gastropoda with over ____________ species and includes the __________, limpets, and slugs. Gastropoda is the
___________ and most varied molluscan class with species occupying ___________, freshwater, and terrestrial habitats. One
of the most important ________________ of the molluscan body form in the gastropods occurs early in development.
_____________ is a ____________, counterclockwise _____________ of the visceral mass, mantle, and mantle cavity.
Torsion positions the gills, __________, and openings from the excretory and reproductive systems just behind the ________
and nerve cords, and twists the digestive tract in to a ________ shape. The earliest fossil gastropods had a shell that was
______________ in one plane. This arrangement is not common in __________ fossils, because growth resulted in an
increasingly cumbersome __________. Most snail shells are _____________________ coiled into a ____________ form.
Nearly all gastropods have a _______________ foot that is often ciliated, covered with ___________ cells, and used to creep
across the substrate. Most gastropods feed by ______________ algae or other small, attached organisms from their substrate
using their _________. Others are _______________ that feed on larger plants, scavengers, _____________, or predators. The
anterior digestive tract is ciliated and contains the ___________. Food is trapped in ____________ strings and is incorporated
into a mucoid mass called the ______________, which extends to the _____________ and is rotated by cilia. A digestive gland
in the visceral mass releases _____________ and acid into the stomach, and food trapped on the ________________ is freed
and digested. Wastes form fecal ___________ in the intestine. Gas exchange always involves the _____________ cavity.
Modern gastropods have ___________ gill due to ______________. Some gastrpods have a rolled extension of the mantle
called a _______________, that serves as an inhalant tube. Gastropods have an ___________ circulatory system, where
____________ leaves the vessels and directly _____________ cells in tissue spaces called _______________. Molluscs have a
______________ consisting of a _________, muscular _____________, and _________ auricles. Most gastropods have
___________ one member of the pair of auricles because of coiling, so they have a __________ auricle and a __________
ventricle. In addition to transporting nutrients, _____________, and gases, the blood of the mollusks acts as a hydraulic
skeleton. A hydraulic skeleton consists of fluid under _________________ that may be confined to tissue spaces to _________
body structures and to ____________ the body. Molluscs ___________ muscles to force fluid into a structure to push it
forward. The nervous system of primitive mollusks is characterized by ________ ganglia located on the ______-_________
and visceral mass, which was twisted by the torsion. The evolution of the gastropod nervous system has resulted in the
_________________ of the nerves and the concentration of nervous tissues into fewer, ____________ ganglia, especially in
the head. Gastropods have __________-______________ sensory structures. Eyes may be at the base or at the end of
_______________. They may be ____________ pits of photoreceptor cells or they may consist of a _________ and cornea.
They have ______________ in the foot and ____________________ chemical receptors for detecting prey. Primitive
gastropods had __________ nephridia, but the modern species, the ____________ nephridia has disappeared due to shell
coiling. The nephridia consists of a ________ with highly folded walls and connects to the reduced _____________, the
pericardial cavity. Excretory wastes are derived from fluids filtered and secreted into the ______________ from the ________.
Many marine snails are _____________________. Gonads lie in ______________ in the visceral mass and ducts discharge
______________ into the sea for external fertilization. Many other snails are ________________, and internal cross
fertilization is dominant. In most marine gastropods, _____________ cleavage results in free-swimming _________________
Larva that develops into another free-swimming larva with foot, ____________, tentacles, and shell called a ______________
larva. _______________ occurs during the veliger stage, followed by settling and metamorphosis to the ______________.
Class Bivalvia
There are around _____________ species of the class Bivalvia. This is the ____________ largest class of mollusks which
includes the __________, oysters, mussels, and scallops. A sheetlike mantle and a shell consisting of ________________
valves cover the animals. Many bivalves are _______________, and some form ____________. Most bivalves are __________
_______________, and are valuable in removing ______________ from polluted water. The two convex halves of the shell are
called _______________. Along the ______________ side of the shell is a _____________ ligament and a series of tongue
and groove modifications of the shell called _______________, that prevent the valves from twisting. The ___________ part
of the shell is the ________________, a big hump area near the shell’s anterior side. The elastic hinged-ligament is made of
protein and allows the valves to _______________ when certain muscles relax. ______________ muscles at either end of the
dorsal half of the shell ____________ the shell for protection from _____________. The bivalve _____________ attaches to
the shell around the adductor muscles near the shel1 margin. If a ____________ grain or a parasite lodges between the shell
and the mantle, the mantle secretes _____________ around the irritant, gradually forming a ____________. Bivalve
adaptations to sedentary, _____________-_________________ lifestyles include the ____________ of the head and radula and
except for a few bivalves the expansion of _________-covered gills. ___________ form folded sheets with one end attached to
the ___________ and the other end attached to the _______________. The mantle cavity ____________ to the gills is the
inhalant region, and the cavity ______________ to the gills is the exhalant region. __________ move water into the mantle
cavity through a ____________ opening of the mantle, which is at the end of the ______________, which is an extension of
the mantle. A bivalve buried in the substrate can extend its ______________ to the surface and still ____________ and
exchange gases. The ____________ trap food particles brought into the mantle cavity, ____________ move the particles to the
_____________, then move the food toward the __________. Cilia covering leaflike ____________ ____________ on either
side of the mouth also sort filtered food particles. The rejected materials are moved to the _____________ and water rushing
out when valves are forcefully _____________ washes the waste from the mantle cavity. The ____________ tract of bivalves
is similar to that of other mollusks. Food entering the _______________ entangles in a mucoid food string, which extends to
the ______________ and is rotated by cilia lining the digestive tract. _______________ function in digestion and partially
digested food from the _____________ enters the digestive gland for _______________ digestion. Cilia carry undigested
wastes in the digestive gland back to the _________________ and then to the _________________. The intestine empties
through the __________ near the ______________ opening, and excurrent ________ carries feces away. Bivalves have an
___________ circulatory system. Blood flows from the ___________ to tissue sinuses, nephridia, ___________, and back to
the heart. The ______________ system consists of _____________ pairs of interconnected ganglia associated with the
esophagus, the foot, and the _______________ adductor muscle. Most bivalves are ______________, with a few being
_________________. _____________ are in the visceral mass, where they surround the looped ____________. Most bivalves
exhibit ______________ fertilization. _____________ exit through the suprabranchial chamber of the mantle cavity and the
exhalant opening. Development proceeds through _________________ and veliger stages. When the ____________ settles to
the substrate it assumes the ___________ form. Most ________________ bivalves ____________ their young Fertilization
occurs in the mantle cavity by ______________ brought in with inhalant water. Some brood their young in _____________
gills trough reduced trocophore and veliger stages. Young clams are __________ from the gills. Bivalves are in nearly all
______________ habitats. They may completely or partially ____________ themselves in sand or mud, attach to solid
substrates, or bore into submerged wood, coral, or limestone.
Class Cephalopoda
The class Cephalopoda includes the octopuses, ___________, cuttlefish, and nautiluses. They are the most ______________
mollusks. The anterior portion of their ___________ has been modified into a circle of ____________ or arms used to capture
prey, attachment, ___________________, and copulation. The foot is also incorporated into a funnel associated with the
mantle cavity and is used for _______________ propulsion. The molluscan body plan is further modified in that the
cephalopod ___________ is in line with the _____________ mass. Cephalopods have a highly _______________ mantle that
encloses all of the ___________ except the head and tentacles. The mantle acts as a _____________ to bring large quantities of
______________ into the mantle cavity. Ancestral cephalopods probably had a conical ____________, and the only living
cephalopod to possess an external coiled shell is the _____________. As the nautilus grows, it moves forward, ____________
new shell around itself and leaving behind the old septum. Only the __________ chamber is occupied and when formed the
chambers are ____________-_____________. The amount of _____________ in the chambers is regulated to alter the
_____________________ of the animal. In all other cephalopods the shell is reduced or ____________. In cuttlefish the shell
is _____________ and laid down in ______________ layers, leaving small gas-filled spaces to increase _________________.
The shell of the squid is reduced to an ______________, chitinuos structure called the __________. Squid also have
cartilaginous ____________ in the mantle wall, neck, and head that ________________ the mantle and _____________ the
brain. The shell is __________ in octopuses. As _______________, cephalopods depend on their ability to move quickly using
a ________-______________ system. The mantle of the cephalopod contains ____________ and ____________ muscles.
Circular muscles __________, ______________ the volume of the mantle cavity and ____________ the collarlike valves to
prevent water from moving _________ of the mantle cavity between the head and mantle wall. Water is forced _______ of a
narrow funnel where muscles attach to the funnel and control the direction of the animal’s _________________. ___________
muscles _____________ water into the mantle cavity by ______________ he cavity’s volume. Posterior __________ act as
stabilizers in squid and aid in propulsion and ______________ in cuttlefish. Most cephalopods locate their prey by _________
and capture prey with ___________ that have adhesive cups. All cephalopods have ____________ and a radula. The jaws are
powerful beaklike structures for ____________ food, and the radula rasps food, ____________ it into the mouth cavity.
Cuttlefish and nautiluses feed on small _______________ on the ocean floor. Octopuses are _______________ hunters and
feed on snails, ___________ and crustaceans. Octopuses have salivary glands that inject ____________ into prey. Squid feed
on fish and shrimp, which they kill by biting across the back of the __________. The ___________ tract of cephalopods is
________________ and peristalsis replaces ciliary action in moving food. Most digestion occurs in a ____________ and a
large cecum. Digestion is primarily ______________ with large digestive glands supplying _______________. An intestine
ends at the ________, near the funnel, and exhalant water carries wastes out of the mantle cavity. Cephalopods, unlike other
mollusks have ______________ circulatory systems. Blood is ___________ to vessels throughout its circuit around the body.
Capillary beds connect _____________ and ________, and exchanges of gases, nutrients, and metabolic wastes occur across
capillary walls. They have a heart with __________ auricles and ___________ ventricle. Cephalopods exhibit ____________
excretory efficiency due to the closed circulatory system. A closed association of blood vessels with nephridia allows wastes to
filet and secrete directly from the ____________ into the excretory system. The cephalopods have a ___________ nervous
system with a _____________ brain. The brain forms by ___________ of ganglia. Large areas are devoted to controlling
muscle contractions, ____________ perception, and functions such as ______________ and decision making. Cephalopods
have pigment cells called _______________________. When tiny muscles attached to these pigment cells contract, the
chromatophores quickly expand and ____________ the ____________ of the animal. Color changes, in combination with
______ discharge function in alarm responses. All cephalopods possess an ________ gland that opens just behind the ______.
Ink is ________ or ___________ fluid containing melanin and other chemicals. Discharged ink __________ a predator,
allowing the cephalopod to escape. Cephalopods are _______________ with __________ in the dorsal portion of the visceral
mass. The __________ reproductive tract consists of ____________ and structures for encasing sperm in packets called
________________________. The ____________ reproductive tract produces large, yolky __________ and is modified with
glands that secret gel-like cases around eggs. One tentacle of the __________ is called the _________________ and is
modified for spermatophore transfer. Cephalopods develop in the confines of the __________ membranes, and the hatchlings
are miniature adults. Young are ___________ cared for after hatching.
Class Polyplacophora
The class Polyplacophora contains the ____________, which are common inhabitants of hard substrates in shallow _________
water. Chitons have a reduced __________, a flattened __________, and a shell that divides into ___________ articulating
dorsal valves. A muscular mantle that extends beyond the margins of the ______________ and foot covers the broad foot. The
mantle cavity is restricted to the space between the margin of the mantle and the __________. Chitons ___________ over their
substrate in a manner similar to gastropods, by attaching their foot to the substrate with a tight ___________. A linear series of
_________ is in the mantle cavity on each side of the foot. Cilia on the gills create __________ _______________ that enter
below the anterior mantle margins and and ____________ posteriorly. The digestive, ______________, and reproductive tracts
open near the exhalant area of the mantle cavity, and _____________ water carries products of these systems away. Most
chitons feed on attached ______________. A ________________ extends from the mouth to detect food that the radula rasps.
Mucus ___________ the food, enters the _____________, extracellular digestion and absorption occur in the ___________,
and wastes move on to the intestine. The ______________ system is ladderlike with ___________ anteroposterior nerve cords
and numerous tranverse nerves. A __________ __________ encircles the esophagus. Sexes are _____________ in chitons.
_____________ fertilization and development result in a swimming trochophore that settles and metamorphoses into an
____________ without passing through a ______________ stage.
Class Scaphopoda
Members of the class Scaphopoda are called __________ shells or _________________ shells. The over _________ species
are all __________________ ___________ animals that inhabit moderate depths. Their most distinctive characteristic is a
________________ shell that is _____________ at both ends. The head and foot project from the ____________ end of the
shell, and the rest of the body, including the mantle is greatly elongate and extends the ______________ of the shell.
______________ and _________________ water enters and leaves the mantle cavity through the opening at the ___________
of the shell. Functional ___________ are absent, and gas exchange occurs across mantle folds. They have a __________ and
________________, which they use to feed on foraminiferans Sexes are ____________, and trochophore and veliger larvae are
produced.
Class Monoplacophora
Members of the class Monoplacophora have an ____________________. Arched shell, a broad ____________ foot, and
repeated pairs of ____________ and foot-retractor _______________. They are __________________. This group of mollusks
is only known from ______________ until 1952, when one was dredged up from the coast of Costa Rica.
Class Aplacophora
Members of the class Aplacophora are divided into __________ subclasses, Neomeniomorpha called solengasters and
Chaetodermomorpha (Caudofoveata), that are wormlike. Solengaster mollusks are ____________________, lack a _________
and crawl on their _____________ surface. The later Caudofoveata are very small and have scalelike spicules on the body wall
and lack the typical mollusk characteristics: ____________, crystalline style, statocysts, ___________, and nephridia.