Transcript small gray snail

What are Mollusks?
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The name Mollusca (from the Latin mollis meaning soft), was first used by the
French zoologist Cuvier in 1798 to describe squids.
All mollusks have a muscular foot (used for moving) and a mantle (an
outgrowth that covers the animal).
Most mollusks have an external calcium carbonate shell that is produced by
the mantle.
All body systems are present.
Many also have a radula (a unique organ that is mostly composed of a hard
material called chitin) in the mouth that allows the animal to scrape food from
surfaces by sliding back and forth. Like a rasping tongue.
Mollusks have a coelom (a body cavity), but the coelom is made from cell
masses, making all species in this phylum protosomes. All organs are
suspended in this coelom, between the outer covering and the digestive tube of
the animal. However, animals in this phylum are unique to coelomates in that
they lack body segmentation.
Taxonomy
Body Systems of Mollusks
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Respiratory- diffusion still occurs (through mantle) but specialized gills, lungs
present (derived from mantle).
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Circulatory- pumping heart, vessels and sinuses; open system in all but cephalopods;
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Hemocyanin- oxygen combining pigment or “blood” that contains copper and is bluish when
combined with oxygen.
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Digestive- complete and complex; mouth to anus.
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Excretory- 2 nephridia (kidneys) empty into mantle cavity.
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Nervous- ganglia and connecting nerve cord; specialized eye in cephalopods.
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Reproductive- most are dioecious (unisexual), but some gastropods are monoecious
(heterosexual).
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Phylum: Molluska
 The 7 major classes belonging to Mulluska.
 Aplacophora - Mollusks without shells
 Bivalvia – Clams and their relatives
 Cephalopoda – Squids and their relatives
 Gastropoda - Snails and their relatives
 Monoplascophora - Mollusks with one plate
 Polyplacophora – Chitons
 Schapoda - Mollusks with a tubular shell
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Class: Aplacophora
(belongs to Phylum: Molluska)
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This class includes two subclasses called Caudofoveata and Solenogastres.
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Both classes contain relatively few species. The Caudofoveata are aberrant
molluscs which lack shells. They normally burrow in soft sediments and are
quite common in the deep sea. The class Solenogastres is also very small.
These animals also lack shells and generally live epibenthically (on the surface
of the substratum).
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They usually resemble worms, and are found in deep water, often more than
3,000 m. There are only about 300 species in this class, and besides lacking
shells, they are all marine and generally very small.
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NONE OF OUR SAMPLES BELONG TO APLACOPHORA.
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Chaetoderma canadense
(an Aplascophoran)
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Class: Bivalvia
(belongs to Phylum: Molluska)
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The bivalves are bilaterally symmetrical (can be divided along their length into two
mirrored - right and left halves) with extensive mantle lobes which secrete a single shell
composed of two valves. The two valves of the shell are hinged dorsally where they are
held together by a new structure, the ligament, and completely enclose the rest of the
body. The valves are closed by two large muscles. Bivalve respiration and locamotion
reflect the morphology described.
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Class Bivalvia includes all of the bivalves. These are marine animals with a hinged shell
divided into two halves. The hinge is head together by a ligament and one or two
adductor muscles. Most live in sand or mud, and use their foot for digging and anchoring
to surfaces. These bivalves use the hinges to take in food, and are also able to jet some
distance away by closing the hinged shell and squirting the water taken in out of the
mantle cavity. Bivalves lack a head and have a spacious mantle cavity as well. Some
examples include clams, oysters, scallops, and mussels.
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The bivalves are mainly marine, but a few species are found in freshwater habitats,
although none have invaded the land. Many species of bivalve are of commercial
importance.
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Respiration in Bivalves
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The mantle cavity of bivalves is greatly expanded and now surrounds the rest
of the body. Inside the mantle cavity are the large leaf-like ctenidia (feathery or
comb-like structures), each of which consists of a dorsal (the back of an organ
or body) vascular axis from which hang an inner and outer gill plate, or
demibranch, made up of numerous parallel gill filaments.
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Each plate is not single, but is folded back on itself in a V-shape and thus has
an ascending and a descending lamella. The two plates, when seen in cross
section have a W-shape.
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Usually the lamellae are held together by junctions of different types;
interlamellar junctions join the lamellae together and interfilamentar junctions
join the adjacent filaments together. The more primitive bivalves, e.g. the
mussel family, possess filibranch gills in which the interfilamentar junctions are
only patches of interlocking cilia.
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Shape of lamellar plates
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Bivalve Locomotion
 Most bivalves are sedentary and many are adapted for
burrowing into soft sediments using the laterally
compressed foot. A few are capable of boring into wood,
and some are even able to bore into rock.
 Although most bivalves are sedentary, some, especially
members of the scallop family, are able to swim actively
over short distances, usually to escape potential predators.
 The scallops swim by rapidly ejecting water from the
mantle cavity by rapid clapping together (adduction) of the
shell valves, which forces water out on either side of the
hinge. Scallops usually swim in short bursts, but may cover
several metres at a time.
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Orders belonging to
Class: Bivalvia
 Major orders belonging to Mollusca/Bivalvia.
 Arcoida
 Myoida
 Mytiloida
 Pterioida
 Unionoida
 Veneroida
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Order: Arcoida
(belongs to Class: Bivalvia)
 Major families belonging to
Molluska/Bivalvia/Arcoida
 Arcidae (Ark shells)
 Glycymerididae (Bittersweet clams)
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Family: Arcidae
(belongs to Order: Arcoida)
 These shells almost always have straight
hinge lines and strong umbones. Most are
ovate.
 Major Genera and species
 Anadara
– brasiliana (Incongruous Ark)
– transversa (Transverse Ark)
 Noetia
– ponderosa (Ponderous Ark)
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Family: Glycymerididae
(belongs to Order: Arcoida)
 These shells have V-shaped ligaments and
many teeth. They are usually round or
broadly ovate.
 Major Genera and species
 Glycymeris
– pectinata (Comb Bittersweet)
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Order: Myoida
(belongs to Class: Bivalvia)
 Major families belonging to
Molluska/Bivalvia/Myoida
 Pholadidae (Piddocks)
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Family: Pholadidae
(belongs to Order: Myoida)
 Major Genera and species
 Cyrtopleura
– costada (Angel Wing)
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Order: Mytiloida
(belongs to Class: Bivalvia)
 Major families belonging to
Molluska/Bivalvia/Mytiloida
 Mytilidae (Mussels)
 Pinnidae (Pen shells)
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Family: Mytilidae
(belongs to Order: Mytiloida)
 Major Genera and species
 Geukensia
– demissa (Atlantic Ribbed Mussel)
 Ischadium
– recurvum (Hooked Mussel)
 Modiolus
– americanus (Tulip Mussel)
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Family: Pinnidae
(belongs to Order: Mytiloida)
 Major Genera and species
 Altrina
– rigida (Stiff Pen Shell)
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Order: Pterioida
(belongs to Class: Bivalvia)
 Major families belonging to
Molluska/Bivalvia/Pterioida
 Anomiidae (Jingle shells)
 Ostreidae (Oysters)
 Pectinidae (Scallops)
 Plicatulidae (Kitten’s Paws)
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Family: Anomiidae
(belongs to Order: Pterioida)
 Major Genera and species
 Anomia
– simplex (Common Jingle Shell)
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Family: Ostreidae
(belongs to Order: Pterioida)
 Major Genera and species
 Crassostrea
– virginica (Eastern Oyster)
 Ostrea
– equestris (Crested Oyster)
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Family: Pectinidae
(belongs to Order: Pterioida)
 Major Genera and species
 Argopecten
– gibbus (Calico Scallop)
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Family: Plicatulidae
(belongs to Order: Pterioida)
 Major Genera and species
 Plicatula
– gibbosa (Kitten’s Paw)
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Order: Unionoida
(belongs to Class: Bivalvia)
 Major families belonging to
Molluska/Bivalvia/Unionoida
 NONE OF OUR SAMPLES BELONG TO
Unionoida.
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Order: Veneroida
(belongs to Class: Bivalvia)
 Major families belonging to Molluska/Bivalvia/Veneroida
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Cardiidae (Cockles)
Carditidae (Carditas)
Cultellidae (Razor clams)
Donacidae (Donaxes)
Lucinidae (Lucines)
Mactridae (Surf clams)
Petricolidae (Petricolas)
Semelidae (Semeles)
Solecurtidae (Razor clams)
Solenidae (Razor clams)
Tellinidae (Tellins)
Veneridae (Venus clams)
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Family: Cardiidae
(belongs to Order: Veneroida)
 Major Genera and species
 Dinocardium
– robustum (Giant Atlantic Cockle)
 Trachycardium
– egmontianum (Prickly Cockle)
– muricatum (Yellow Cockle)
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Family: Carditidae
(belongs to Order: Veneroida)
 Major Genera and species
 Carditamera
– floridana (Broad-ribbed Cardita)
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Family: Cultellidae
(belongs to Order: Veneroida)
 Major Genera and species
 Ensis
– directus (Common Razor Clam)
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Family: Donacidae
(belongs to Order: Veneroida)
 Major Genera and species
 Donax
– variabilis (Florida Coquina)
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Family: Lucinidae
(belongs to Order: Veneroida)
 Major Genera and species
 Divaricella
– quadrisulcata (Crosshatched Lucine)
 Parvilucina
– multilineata (Multi-lined Lucine)
 Phacoides
– pectinatus (Thick Lucine)
 Pseudomiltha
– floridana (Florida Lucine)
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Family: Mactridae
(belongs to Order: Veneroida)
 Major Genera and species
 Mactra
– fragilis (Fragile Atlantic Mactra)
 Mulinia
– lateralis (Dwarf Surf Clam)
 Raeta
– plicatella (Channeled Duck Clam)
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Family: Petricolidae
(belongs to Order: Veneroida)
 Major Genera and species
 Petricola
– pholadiformis (False Angel Wing)
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Family: Semelidae
(belongs to Order: Veneroida)
 Major Genera and species
 Cumingia
– tellinoides (Tellinlike Cumingia)
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Family: Solecurtidae
(belongs to Order: Veneroida)
 Major Genera and species
 Tagelus
– plebeius (Stout Tagelus)
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Family: Solenidae
(belongs to Order: Veneroida)
 Major Genera and species
 Solen
– viridis (Green Jackknife Clam)
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Family: Tellinidae
(belongs to Order: Veneroida)
 Major Genera and species
 Tellina
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alternata (Alternate Tellin)
iris (Iris Tellin)
sybaritica (Dall’s Dwarf Tellin)
tampaensis (Tampa Tellin)
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Family: Veneridae
(belongs to Order: Veneroida)
 Major Genera and species
 Chione
– cancellata (Cross-barred Venus)
 Dosinia
– discus (Disk Dosinia)
 Macrocallista
– numbosa (Sunray Venus)
 Merceneria
– campechiensis (Southern Quahog)
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Class: Cephalopoda
(belongs to Phylum: Molluska)
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This class contains the squids, octopuses and cuttlefish.
Orientation of the body differs from most mollusks in that the ventral region
(belly-side) is now anterior (up front) and the visceral mass is now the
functional posterior (in back) end of the animal. This change in orientation has
implications for sensory function and cephalopod locomotion.
Also differs from other mollusks in the alteration of much of the original foot into
a series of large prehensile tentacles or arms at the anterior end which now
surround the head.
Most either have an internal shell, like a squid. Some lack a shell, like an
octopus. All cephalopods are predators, and use jaws and radula to crush and
rip prey. Like bivalves, they are able to move by taking water into the mantle
cavity and shooting it back out.
They have large brains enclosed in cartilaginous brain cases. Because of a
developed brain, good eye sight, and good sense organs, they are considered
to be one of the most advanced invertebrates.
NONE OF OUR SAMPLES BELONG TO CEPHALOPODA.
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Octopus
(a Cephalopod)
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Eye of an Octopus
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Cephalopod Locomotion
 Most cephalopods, except the more sedentary octopus, are active
animals, which swim by means of jet propulsion, during which water is
rapidly forced out of the mantle cavity through the siphon by the
contraction of the muscles in the mantle wall.
 Squids, besides being the fastest cephalopods, are also the fastest
swimmers of all aquatic invertebrates. Their long tapered bodies are
ideally streamlined, and the lateral fins provide stability. The 'flying
squids' are particularly interesting. These have highly developed fin
vanes and may shoot out of the water and glide for some distance.
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Cephalopod Tentacles
 Squids and cuttlefish have ten appendages comprised of
eight arms and two long tentacles possessing numerous
cup-shaped, rimmed suckers. The tentacles are used to
capture prey, which is held by the tentacles and their
suckers as it is pulled towards the mouth.
 The mouth lies at the base of the tentacles and possesses
a parrot-like beak.
 The octopuses have eight long tentacles (sometimes called
arms) each with a row of suckers on the inner surface.
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Class: Gastropoda
(belongs to Phylum: Molluska)
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Gastropods are the most successful group of molluscs not only in terms of the number of
species, but also in the wide range of habitat in which they may be found. Marine species
have become adapted to living on all types of substratum and some have even adopted
a pelagic (living in open water either at the surface or at intermediate depths) existence.
Others have successfully invaded all types of freshwater habitat as well as the land.
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A univalve, generally spirally coiled shell is present in the majority of gastropods. The
most significant change from the hypothetical ancestral mollusc that the gastropods have
undergone during their phylogeny is the process of torsion. The third important feature of
gastropods is the greater degree of head development or cephalization.
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Class Gastropoda is the largest group of mollusks, with between 40,000 and 75,000
species. These are also the only mollusks that live on land. Gastropods, like Class:
Schapoda, lack gills, and use the mantle as a makeshift lung for extracting oxygen and
breathing. Most species have coiled shells, and this class has evolved tentacles and
eyes. This class includes marine animals like the sea slug and terrestrial animals like the
slug and snail.
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Gastropod Shell Coiling
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One characteristic feature of the majority of gastropods is that the ancestral
conical shell has now become coiled. This process was a separate
evolutionary event and was not connected with torsion, indeed there is fossil
evidence that it may have preceded it. In the most primitive gastropods, shell
coiling was planospiral, whereas in the more advanced forms coiling is
asymmetrical.
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In this type of shell, the shell axis has now become shifted slightly to improve
weight distribution and in modern forms it is carried obliquely to the long axis of
the body, and its weight is now borne by the widest part of the foot, near the
middle of the body.
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The symmetrical shell and the angle at which it is carried has caused some
occlusion of the mantle cavity on the right side, which in turn has resulted in the
reduction or loss of the right ctenidium and the associated auricle. The shape
of a gastropod's shell depends greatly on its habitat and its mode of life.
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Gastropod Torsion
 The most significant change from the hypothetical ancestral mollusc
that the gastropods have undergone during their phylogeny is the
process of torsion. During torsion, most of the body behind the head,
including the mantle, mantle cavity and visceral mass are twisted anticlockwise through 180 degrees.
 Not all living gastropods are torted, however. Some groups have
undergone detorsion during which the mantle cavity has moved to
within 90 degrees of its original position, occasionally even 120
degrees in some species, and has resulted in some rearrangement of
the internal anatomy.
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Orders belonging to
Class: Gastropoda
 5 major orders belonging to
Molluska/Gastropoda
 Archaeogastropoda
 Caenogastropoda
 Heterogastropoda
 Nudibranchia
 Sigmurethra
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Order: Archaeogastropoda
(belongs to Class: Gastropoda)
 Major families belonging to
Molluska/Gastropoda/Archaeogastropoda
 Turbinidae (Turban shells)
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Family: Turbinidae
(belongs to Order: Archaeogastropoda)
 These shells are turban- or top-shaped, or
occasionally flattened. They are thick,
sculptured or smooth, with a rounded
aperture that is pearly within.
 Major Genera and species
 Turbo
– castanea (Chestnut Turban)
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Order: Caenogastropoda
(belongs to Class: Gastropoda)
 Major families belonging to
Molluska/Gastropoda/Caenogastropoda
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Conidae (Cone shells)
Crepidulidae (Cup-and-saucer shells or slipper shells)
Fasciolariidae (Spindle shells)
Ficidae (Fig shells)
Melongenidae (Crown conch shells)
Muricidae (Murex shells)
Nassariidae (Dog whelk or Basket whelk shells)
Naticidae (Moon shells)
Olividae (Olive shells)
Terebridae (Auger shells)
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Family: Conidae
(belongs to Order: Caenogastropoda)
 These shells are cone-shaped (narrow at
bottom, wide at shoulder) with a low spire.
 Major Genera and species
 Conus
– floridanus (Florida Cone)
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Family: Crepidulidae
(belongs to Order: Caenogastropoda)
 These shells are either cap-shaped or
slipper-shaped with a shelf underneath.
 Major Genera and species
 Crepidula
– convexa (Convex Slipper Shell)
– fornicata (Atlantic Slipper Shell)
– plana (Eastern White Slipper Shell)
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Family: Fasciolariidae
(belongs to Order: Caenogastropoda)
 These shells are usually large and are
generally spindle-shaped.
 Major Genera and species
 Fasciolaria
– tulipa (True Tulip)
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Family: Ficidae
(belongs to Order: Caenogastropoda)
 These shells are thin and have the shape of
a large fig or a slender pear.
 Major Genera and species
 Ficus
– communis (Common Fig Shell)
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Family: Melongenidae
(belongs to Order: Caenogastropoda)
 These shells are usually large with a large
body whorl and a low to elongately conical
spire.
 Major Genera and species
 Busycon
– canaliculatum (Channeled Whelk)
– carica (Knobbed Whelk)
– contrarium (Lightning Whelk)
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Family: Muricidae
(belongs to Order: Caenogastropoda)
 These shells usually have spines, but some
have strong ribs instead.
 Major Genera and species
 Eupleura
– caudata (Thick-lipped Drill)
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Thick-lipped Drill
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Family: Nassariidae
(belongs to Order: Caenogastropoda)
 These are small snail shells that are usually
elongate and conical.
 Major Genera and species
 Nassarius
– obsoletus (Eastern Mud Whelk)
– trivittatus (New England Basket Whelk)
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Family: Naticidae
(belongs to Order: Caenogastropoda)
 These shells are round to broadly ovate.
They are usually smooth with short spires.
 Major Genera and species
 Neverita
– duplicata (Shark’s Eye)
 Sinum
– perspectivum (Common Atlantic Baby’s Ear)
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Family: Olividae
(belongs to Order: Caenogastropoda)
 These shells are elongate and cylindrical.
They have a narrow aperture and a small
conical spire.
 Major Genera and species
 Oliva
– sayana (Lettered Olive)
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Lettered Olive
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Family: Terebridae
(belongs to Order: Caenogastropoda)
 These shells are high, narrow, and elongate,
with numerous whorls. The surface may be
smooth or have spiral grooves.
 Major Genera and species
 Hastula
– cinerea (Gray Atlantic Auger)
 Terebra
– dislocata (Common American Auger)
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Common American Auger
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Order: Heterogastropoda
(belongs to Class: Gastropoda)
 Major families belonging to
Molluska/Gastropoda/Heterogastropoda
 Epitoniidae (Wentletrap shells)
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Family: Epitoniidae
(belongs to Order: Heterogastropoda)
 Almost all of these shells are white with
convex whorls and roundish apertures.
 Major Genera and species
 Epitonium
– angulatum (Angulate Wentletrap)
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Angulate Wentletrap
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Order: Nudibranchia
(belongs to Class: Gastropoda)
 Major families belonging to
Molluska/Gastropoda/Nudibranchia
 NONE OF OUR SAMPLES BELONG TO
Nudibranchia.
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Order: Sigmurethra
(belongs to Class: Gastropoda)
 Major families belonging to
Molluska/Gastropoda/Sigmurethra
 NONE OF OUR SAMPLES BELONG TO
Sigmurethra.
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Class: Monoplascophora
(belongs to Phylum: Molluska)
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This is a very small group of organisms that has been known for only a short time.
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Originally thought to exist only in the fossil record, they were rediscovered in 1952, and
there are now about ten known species, all of which are deep ocean dwellers. This class
is characterized by having an unhinged shell.
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The animals possess a large flattened foot surrounded by the pallial groove, in which are
situated 5 or 6 pairs of gills. Internally, the animals possess 8 pairs of dorso-ventral pedal
retractor muscles, a feature that is known to have existed in fossil forms.
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They also show a number of distinct characteristics such as the possession of 6 pairs of
nephridia (excretory organ having function of kidney in invertebrates) lying in the pallial
groove. The coelom consists of the pericardial cavity and the cavity of the two pairs of
gonads.
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NONE OF OUR SAMPLES BELONG TO MONOPLASCOPHORA.
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Structure of Neopolina
(a Monoplascophoran)
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Class: Polyplacophora
(belongs to Phylum: Molluska)
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This class includes the chitons.
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The shells of chitons are characteristically divided into 8 transverse, overlapping shell
plates or valves. The foot is greatly expanded, forming a large flattened sole which is
used not only for locomotion but also for maintaining firm contact with the rock surface.
Adhesion is effected mainly by the foot under normal conditions but, when the animal is
disturbed, the girdle (the soft part surrounding the shell) is also clamped down tightly
onto the rock surface.
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Chitons feed on small particles of algae on the rock surface which are scraped off using
the radula. Feeding normally takes place when covered by the tide, and they tend to be
most active when immersed at night. They are normally inactive animals and move only
to feed, but often show 'homing behaviour', which enables them to return to the same
area of rock.
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NONE OF OUR SAMPLES BELONG TO POLYPLACOPHORA.
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Chiton glaucus
(a Polyplacophoran)
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Class: Schapoda
(belongs to Phylum: Molluska)
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One of the smaller classes of molluscs, the scaphopods, or tusk shells, are burrowing,
marine molluscs having a tubular tusk or tooth-shaped shell which is open at both ends.
They are elongated along the anterior-posterior axis and live buried in the sand, head
downwards, with the body steeply inclined. Water enters and leaves the mantle cavity via
the posterior aperture.
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The head is very reduced and lacks eyes, but is surrounded by numerous thread-like
tentacles or captacula. The captacula possess an adhesive knob at their tip and are used
to gather small particles of food present in the sand and pass them to the mouth.
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Scaphopods are found mainly in the deep sea, but a few species occur in shallow
water.This class is unusual because it lacks both gills and heart. Therefore, gas
exchange occurs in the mantle and blood is circulated by contractions of the foot.
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NONE OF OUR SAMPLES BELONG TO SCHAPODA.
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Graptacme eborea
(a Shapodan)
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