Transcript Phylum Mollusca - Loyola Blakefield

PHYLUM MOLLUSCA
Cephalopods, Gastropods, Bivalves
and their Relatives
Characteristics of the Group
• Most numerous phylum in the ocean by number
of species (200,000)
• Soft bodied with a calcium carbonate shell
• Bilaterally symmetrical but not always
• Most have a head region with eyes and other
sensory organs
Other Characteristics of Molluscs
• Unsegmented
• Molluscs are coelomates, although the coelom is reduced
• Separate mouth and anus; have salivary and digestive
glands that release digestive enzymes
• Gas exchange through paired gills
• Ubiquitous in marine environments; can be found from
intertidal zones to the deepest oceans
• Have a head, foot, and body in some arrangement
http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/mollusca.php
Unique Structures
• Mantle – thin layer of tissue
that secretes the shell.
• Foot – ventral, muscular
organ that is used in
locomotion (sometimes
modified into tentacles)
• Radula – ribbon of small teeth
made of chitin (tough
carbohydrate) that are used in
feeding
Mollusc Body Plan
Intestine
Shell
Gonad
Stomach
Heart
Digestive Gland
Mantle
Gill
Foot
Nervous System
Radula
Types of Molluscs
• Gastropods –
• Snails, limpets, abalones, nudibranchs, whelks
• Bivalves –
• Clams, mussels, oysters
• Cephalopods –
• Octopus, squid, cuttlefish
Mulluscs: The Survival Game
“The ability to change in the ever-changing world is
perhaps the greatest secret in the survival game.”
• Watch the video: http://vimeo.com/37325960
• Identify the evolutionary advances in the three types of
molluscs.
Gastropods
• Means “stomach footed”
• Most numerous and varied
group of molluscs
• (~75, 000)
• The only group to invade
terrestrial niches
• Include snails,
limpets, abalones, and
nudibranchs
Characteristics of Gastropods
• “Coiled mass of vital organs surrounded by a dorsal shell”
• Have a ventral foot typically used for crawling; may be
modified for burrowing, leaping, swimming, or clamping
• With their radula they inhabit most all feeding niches –
carnivores, detritivores, herbivores
• Shells can be very elaborate, may be internal, or could be
missing entirely (nudibranchs).
Parts of a Gastropod Shell
Gastropod Shells
Left-handed or right-handed?
Nudibranchs
(http://www.youtube.com/watch?v=nHVoV0MVwSc)
• Sea slugs
• Name means
“naked gill”
• Have lost the
shell entirely
• Usually brightly colored
• Can keep and incorporate noxious
chemicals and undischarged nematocysts
from prey for defense.
Bivalves
• Have a two-valved, hinged shell.
• Body is laterally compressed.
• No head or radula
• Gills are used to obtain oxygen and filter food
• Mantle surrounds body.
• Strong muscles are used to close the valves of the shell
• Many bivalves use their foot for burrowing
Clams
• Burrow in sand and mud
• Use siphons to move
water in and out –
permits eating and
respiring while buried.
• Some contain iridescent
chemicals in their tissues
Clam Anatomy
Mussels & Oysters
• Instead of burrowing, they secrete
byssal threads that attach them to
rocks and other surfaces.
• Oysters cement their left shell to a
hard substrate; sometimes other
oysters creating oyster reefs
• Pearl oysters - thin layer of calcium
carbonate coat irritating particles or
parasites lodged between the
mantle and the inner shell
Oyster Anatomy
Other Bivalves
• Some bivalve bore into coral, rock, or wood.
• The shipworm bore into wood and have symbiotic
bacteria in their gut to digest the wood.
Cephalopods
• Means “head-footed”
• About 650 species
• Body such that head is
between “feet” and body.
• Includes octopuses, squid,
cuttlefishes, and the
chambered Nautilus
Giant Pacific Octopus
Cephalopod Characteristics
• Agile swimmers
• Complex nervous system
• Shell is reduced or lost entirely
• Foot is modified into tentacles usually equipped with
suckers
• Eyes are well developed
• Body protected by thick muscular mantle
• Move by forcing water out of the siphon, a flexible, funnelshaped tube on the side of the head.
Octopuses
• Eight arms and no shell
• Bottom dwellers
• 5cm – 9m
• Predators on crabs, lobster,
shrimp, small fish, and other
molluscs
• Have a hard “beak”
• Some like the blue-ring
secrete a highly toxic venom
in their bite
• Can emit a dark ink to confuse
attackers
Blue ringed octopus
Squid
• Elongate body
• Mantle contains two
triangular fins.
• Eights arms + two
retractable tentacles
• Shell reduced to a
chitinous pen inside the
mantle
• Few cm to 12 m
Cuttlefishes
• Resemble squid but
with a flattened body
and a rippling fin
surrounding the
mantle.
• Have a calcified
internal shell or
“cuttlebone.”
The Chambered Nautilus
• Have a smooth coiled shell
up to 25 cm in diameter.
• Chambers in the shell are
filled with gas to provide
buoyancy
• Has 60-90 short,
suckerless tentacles for
capturing fish
• Living fossil
Molluscan Digestion
• Separate mouth and anus
• Have salivary and digestive glands
• Most use their radula to scrape, drill, cut, or
capture prey.
• Bivalves – radula is absent and food particles
are ingested and filtered by cilia on the gills; have
a crystalline style in their gut that secretes
enzymes.
Molluscan Circulation
• Open circulatory system
• Muscular heart pumps blood to all tissues.
• Cephalopods – closed circulatory system
• Blood contained in vessels
• More efficient – meets the demands of large organs such as the
brain.
Heart
Molluscan Nervous System
• Gastropods and bivalves have ganglia – cluster of nerve
cells
• Cephalopods - large fused brain that is divided into
regions that control particular functions and behaviors.
• Octopus and cuttlefish can learn
(http://www.youtube.com/watch?v=9kuAiuXezIU) .
• Sophisticated color changes are believed to be coordinated by the
nervous system. (http://www.youtube.com/watch?v=2x-8v1mxpR0,
http://www.youtube.com/watch?v=fR7Dqf0vzzQ )
Mollusc Reproduction
• Most have separate sexes, but some are
hermaphrodites
• Some have external fertilization (tusk shells, bivalves,
chitons, & some gastropods)
• Others have internal fertilization - a spermatophore,
or sperm packet is deposited into the female via a
modified arm (cephalopods) or a penis (gastropods).
• Cephalopods lay eggs and the young develop from
the yolk. Female octopus usually die after laying and
guarding eggs – most likely due to starvation.
Mollusc Reproduction continued…
• Some create a trocophore larvae which develops into a
veliger (a planktonic larva with a tiny shell)
• Cephalopods lay eggs and the young develop from the
yolk. Female octopus usually die after laying and guarding
eggs – most likely due to starvation.