Transcript Phylum Mollusca

Phylum Mollusca
“soft bodied”
animals Ch 12
Chordata
Arthropoda
Annelida
Mollusca
Protostomes
†
Triploblasts
* Diploblasts
Hemichordata
Echinodermata
Deuterostomes
Coelomates
Pseudocoelomates
Acoelomates
Bilateria†
Radiata*
Eumetazoa
Mesozoa
Metazoa
Protozoa
Monera (Bacteria)
Cnidaria
Ctenophora
Parazoa
Mollusca Characteristics
Triploblastic
Organ level of organization
Bilateral Symmetry
Cephalization
Eucoelomate
Protostome
Eucoelomate
Have a “true” body cavity that is completely surrounded
by mesoderm
ectoderm
coelom
mesoderm
Gut
endoderm
Mollusca Characteristics
Gas Exchange
• mainly gills, however terrestrial species have evolved
“lungs”
Circulatory System
• open circulatory system (in most classes)
• heart and blood sinuses
Excretion
• most have kidneys (metanephridia)
Nervous system
• ventral nerve cords, sensory organs
Mollusca Characteristics
Digestive System
• complete with regional specialization
• Radula: a tongue-like organ bearing rows of teeth that
is used in feeding (scraping, drilling, etc.)
hole made by a
moon snail radula
Cross section of a Gastropod head
Mollusca Characteristics
Reproduction
• monoecious and dioecious species exist
• usually internal fertilization
• indirect development with the presence of a
trochophore larva (link to annelids), and in most cases
a veliger larva
trochophore
veliger
Mollusca Characteristics
Body Plan
• head-foot: contains sensory organs and muscles
• visceral mass: contains digestive, reproductive,
circulatory organs
• mantle: secretes the shell (if there is one), cavity
contains gills or lungs
•Shell: in most groups.
shell
Visceral mass
foot
mantle
mantle cavity
(Hypothetical Ancestral Mollusc)
gonads
Mantle
coelom
Shell
Nephridium
Anus
Digestive gland
head
Gill
Mouth
Radula
foot
Nerve collar
Nerve cords
Intestine
Molluscan Radiation
• There are approximately 93,000 living species
in phylum Mollusca (70,000 are extinct)
• The great morphological diversity is the
result of elaboration on the basic body plan
Molluscan Radiation
Gastropoda
torsion
coiling of the
shell
Scaphopoda
ventral shell
fusion
Polyplacophora
Solenogastres
Caudofoveata
shell consists of 8
plates
HAM
Shell-less but
scales or
spicules
present
Bivalvia
bivalved shell
dorsal hinge
Cephalopoda
Monoplacophora
Cap-like shell
lobed foot
highly developed
head
shell reduced or
lost
Phylum Mollusca
Class Polyplacophora
Class Gastropoda
Class Cephalopoda
Class Bivalvia
Class Scaphopoda
Class Monoplacophora
Class Soenogastres (Aplacophora)
Class Caudofoveata
Class Polyplacophora
the “chitons”
Class Polyplacophora
• have 8 rows of articulating plates
• use radula to graze algae on substrate
• mantle forms a girdle around plate edge
• no veliger larvae
girdle
plates
Live in Intertidal Zone
All Marine
More Anatomy of a Chiton!
Cryptochiton sp.
• The Gumboot Chiton
The gumboot chiton
• the largest species of
chiton in the world,
growing up to 30 cm in
length
• eight plates are covered
up by thick, leathery,
brick-red flesh so we
cannot see them.
Cryptochiton sp.
Class Gastropoda
snails and slugs
Gastropoda
Origin and Evolution
1.
2.
3.
4.
Development of a head
Dorsoventral elongation of the body
Shell become complex retreat: coiling
Torsion
Torsion
• Torsion is not the spiraling of the shell
• The body behind the head was twisted 180 degrees
counterclockwise
• Organs reversed location
• Gut twisted
mouth
mouth
anus
gills
gills
anus
anus
gills
Coiling
Planospiral shell
Apex of shell
extends out making the
shell more compact
Conispiral shell
Shell shifts over
body for better
weight distribution
Class Gastropoda
Subclass
Prosobranchia
Subclass
Opisthobranchia
Subclass
Pulmonata
Class Gastropoda
Subclass Prosobranchia
• aquatic snails (marine and freshwater)
• have undergone torsion and most have undergone shell
coiling
• have gills
• all have shells
• use radula for feeding; can be herbivores, carnivores, or
detritivores
In some, mantle extends over shell
Class Gastropoda
Subclass Prosobranchia
• snails often lay eggs in protective capsules
Naticidae Moon Snails
Close-up of a moon snail drill hole.
Gastropods in the subclass Prosobranchia all contain
an Operculum on the shell.
Class Gastropoda
Subclass Opisthobranchia
• sea hares and sea slugs (nudibranchs)
• have undergone detorsion
• have gills
• sea hares have a reduced shell
• sea slugs have no shell
Nudibranchs
Ecology
• Molluscs have many different means of defense
• many nudibranchs that feed on
cnidarians collect and store the
undischarged nematocysts in
cnidosacs
• they then can use these
nematocysts for their own
protection
Class Gastropoda
Subclass Opisthobranchia
• sea hares usually crawl along the
bottom but many can also swim by using
their modified mantle as “wings”
Class Gastropoda
Subclass Opisthobranchia
• all are monoecious
• sea hares often form “mating chains”
acts as male
only
act as both males and
females
simultaneously
acts as female
only
Class Gastropoda
Subclass Opisthobranchia
• sea slugs often lay “ribbons” of eggs which
stick to the substrate
A Sea Hare Anaspidean
A Sea Hare
Anaspidean,
Aplysia
dactylomela
A Sea Hare
Anaspidean, Aplysia
dactylomela
A Sea Hare
Anaspidean,
Aplysia
dactylomela
Aplysia gigantea
Internal Shell of Sea
Hare
Sea Hares
Aplysia dactylomela