Cephalopods such as octopuses, squid, and cuttlefish evolved large brains, complex senses, and rapid locomotion for predation, but their numbers have declined dramatically. Vertebrates may have outcompeted cephalopods by developing active predatory lifestyles. Mollusks are a large phylum that includes snails, slugs, mussels and octopuses. They have soft bodies that are sometimes covered by an external shell secreted by the mantle. Mollusks display bilateral symmetry and their body plans generally include a head-foot region and visceral mass.
2. Evolutionary Perspective
Octopuses, squid and cuttlefish are some of the invertebrate
world’s most adept predators. Predatory lifestyle have result in
the evolution of large brains( by invertebrates standards ),
complex sensory structures( by any standards ), rapid
locomotion, gasping tentacles, and tearing mouthparts.
Cephalopods now includes only about 550 species
Zoologist do not know why cephalopods have decline so
dramatically.
Vertebrates may have outcompeted cephalopods because the
vertebrates (bony fish) acquired active, predatory lifestyle.
3.
4. What is Molluscan/ Mollusc?
Came from the Latin word molluscus mean Soft.
They are Triploblastic
Consider second largest animal phylum.
It includes herbivores, carnivores, filter feeder and
parasite.
An invertebrates for a large phylum that includes snail,
slugs, mussels, and octopuses.
They have soft, segmented body and live in aquatic or
damp habitat, and most kinds have an external
Calcareous Shell.
Known as cone shells deliver a painful sting that can be
a lethal to human.
6. Characteristics of Phylum Mollusc.
Body of two parts Head-Foot and Visceral mass.
Mantle that secretes a calcareous shell that covers the
visceral mass.
Mantle Cavity functions in Excretion, Gas exchange,
elimination of digestive waste and release of
reproductive products.
Bilateral symmetry.
Protostome characteristics, including trochophore
larvae, spiral cleavage, and schizocoelous coelom
formation.
Coelom reduce to cavities surrounding the heart,
nephridia, and gonads.
7. Open circulatory system in all but on class
(Cephalopods).
Radula usually present and use in scraping food.
8. The Three main body region of a
Mollusc/ Mollusk
Head-Foot Is the elongated w/ an anterior head
containing the mouth and certain nervous and sensory
structure, and an elongated foot, used for attachments
and locomotion.
Visceral Mass Contains the organs of digestion,
circulation, reproduction, and excretion and is positioned
dorsal to the head-foot. It includes mantle that cover the
visceral mass and may secrete a shell.
9. Mantle Usually attaches to the visceral mass,
enfolds most of the body, and may secrete a shell that
overlies the mantle.
10. Three layers of Shell
Outer layer outer margin that secrete protein
called Periostracum( is a thin organic coating or “skin”
w/c is the outermost layer of the shell of many shelled
animals).
11. Middle Layer is the thickest of the three layer and
consist of calcium carbonate mixed with organic
materials called Prismatic Layer ( producing tissues and
a screen and consisting of calcite or aragonite).
12. Inner Layer forms a thin sheets of calcium
carbonate altering with organic matter called
Nacreous Layer ( also known as Mother of Pearl, is an organic-
inorgani ccomposite material produce by some mollusks as an inner
shell layer; it is also what makes up the outer coating of the pearl).
13. Classification of Mollusca
Class Gastropods ( G. gastro, stomach and podos,
foot).The large stand most divers of the mollusc
classes and it includes the snails, limpers and
slugs, conch, whelks and nudibrach.
Usually found on marine habitats and they are
herbivores.
They have an elongated, flattened foot and a
one-piece coiled shell that protects the visceral
mass
15. Land snail
Such as Helix aspersa
They are Hermaphroditic
They have three obvious division of the body:
1.Head a flat long
2. Muscular foot
3. Visceral mass surrounded by shell and
provide protection from the predator and prevent
desiccation (drying out).
16. Nudibranch
Comes from the L. nudus, naked and brankhia,
gills.
Aquatic Gastropods that have a gill in their mantle
cavity richly supplied with blood vessels, functions
as a lungs when air is moved in and out through
respiratory pores.
Group of soft bodied, marine gastropods mollusks w/c
shed their shell after their larval stage
18. Limpets
Often found living on hard surface in the
intertidal zone.
Can found on in the places rich in algae on
most rocky shores.
They are very hardy species and are even
found on the stormiest shore all year round
20. Whelks
Is the common name that is applied to a
various kinds of sea snail many of which
have historically been used, or are still used,
by humans for food.
They also known as welkor evenwilks. The
word originated from the from the Proto-
Germanic root “weluka”, meaning toturn or
revolve.
22. Conch
A tropical marine mollusks with a spiral
shell that may bear long projection and have
a flared lip.
They also called Concha
Is a common name that is applied to a
number medium to a large-sized sea snail or
other shells.
24. TorsionOne of the most significant modifition of the
molluscan body forms in gastropods occurs early in
development.
Is a 180, counter clockwise twisting of the visceral
mass, mantle, and mantle cavity.
Torsion portions the gills, anus, and openings from the
excretory and reproductive system just behind the
head and nerve cords, and twists the digestive tract
into a U shape.
It is the action of being twisting or the state of
being twisted, especially of one of an object
relative to the another.
