Transcript Mollusca 2010 - The Bronx High School of Science

-Determinate cleavage
-Indeterminate cleavage
“Radiata”
Metazoa
Ancestral colonial
flagellate
Deuterostomia
Eumetazoa
Protostomia
Bilateria
Phylum: Mollusca
Nematoda
Nemertea
Rotifera
Arthropoda
Annelida
Mollusca
Platyhelminthes
Chordata
Echinodermata
Brachiopoda
Ectoprocta
Phoronida
Ctenophora
Cnidaria
Porifera
clam-like
squid/octopu
s-like
snail/slu
g-like
3 main Mollusk body plans evolved
Annelids
ancestral
Mollusk
chiton-like
body plan
ancestral protostome coelomate
Phylum: Mollusks- 4 Classes
Polyplacophora
(chitons)
Bivalva
(clams,oysters)
Cephalopoda
(squid,octopi)
Gastropoda
(snails,slugs)
Phylum: Mollusca
• One of most successful of all phyla (over 150,000 known species)
• Occupy marine, freshwater and land habitats
• Surpassed only by arthropods in number of species
• Named for Latin “molluscus” (soft) for their soft bodies
• Possess durable shells
• Terrestrial forms occur in seasonally moist places (slugs, snails)
• Economic importance
• sources of human food (ex. clams, oysters, scallops,
escargot)
• production of pearls and shell material
• negative impact of zebra mussels (native to Russia), an
invasive species destroying American freshwater ecosystems
• extensive crop, flower damage caused by snails and slugs
• intermediate hosts for some serious parasitic diseases
• Largest of invertebrates- giant squid estimated at 30-50 feet long
zebra mussels- invasive species
economic impact, biological impact
Phylum: Mollusks
Body Plan
•bilateral symmetry, coelomate, protostome
•3 main body areas
•(1) head-foot
•sensory structures at head
•muscular foot adapted for locomotion
•cephalopod foot divided into tentacles (ex. squid)
•free-swimming (pelagic) animal foot modified as fins or winglike
projections (ex. scallop)
•(2) visceral mass
•fleshy body
•contains excretory, digestive, circulatory structures
•(3) mantle
•cavity formed from folds of dorsal body wall
•surrounds visceral mass
•gills are specialized portion of mantle in mantle cavity
•filamentous projections rich in blood vessels
•large surface area, efficient, can extract 50% of oxygen from water
•cilia maintain constant stream of water over gills
•some animals withdraw into mantle for protection
•in shelled animals mantle secretes shell
Phylum: Mollusks
• Most have durable shell
•secreted by mantle
•bivalves may produce pearls of shell material
around foreign objects
•Radula = rasping, tongue-like structure
•in all mollusks except bivalves
•covered w/ row of backward-curving, sharp
teeth
•gastropods (snails) use to scrape algae of
surfaces for food
•some use to puncture prey and extract food
Phylum: Mollusks
• Circulatory system consists of heart and open flowing
system
• 3-chambered heart
• 2 chambers (atria) collect oxygenated blood from
gills
• third chamber (ventricle) pumps blood to body
• heart surrounded by pericardial cavity (= coelem)
• cephalopods (ex. octopus) more complex w/ closed
system of vessels & auxiliary hearts
Phylum: Mollusks
• Excretory system more efficient than in lower
invertebrates
• nitrogenous wastes removed by tubular nephridia
• funnel-shaped, cilia-lined nephrostome collects
waste from coelom
• coiled tube from nephrostome connects to bladder
• bladder connected to excretory pore
• waste discharged into mantle cavity where nutrients
and salts (maintain osmotic balance) are reabsorbed
Phylum: Mollusks
•Reproduction
•most have separate sexes, some
hermaphrodites
•cross-fertilization is rule, even in
hermaphrodites
•some change sexes within one
season
•larva is trochophore
•ciliated for movement
trochophore
larva
Phylum: Mollusks
Class: Polyplacophora (chitons)
• most evolutionarily primitive mollusk
• marine
• body is oval shape
• overlapping calcareous plates on dorsal side
• broad flat foot (contains mucus glands) on ventral side for
locomotion
Phylum: Mollusks
Class: Gastropoda (snails, slugs)
•primarily marine, some freshwater & terrestrial
•some have an operculum- “trap door” shell can pull into
place for protection
•head has paired sensory tentacles, may have terminal
eyes
Phylum: Mollusks
Class: Gastropoda (snails, slugs)
• visceral mass asymmetrical b/c torsion during development
• one side of larva grows faster giving rise to a right-handed coil
• 180˚ turn with respect to head & foot
• nervous system twisted
• digestive, excretory and reproductive system on top of head
• less room on right leads to loss of right gill, right auricle of heart
and nephridium
Phylum: Mollusks
Class: Gastropoda (snails, slugs)
• varied feeding habits- heterotrophs
• examples- (just FYI)
• terrestrial ones herbivores- serious garden pests
• whelks use radula to bore into other mollusk shells and suck out
contents
• cone shells are predators with harpoon-like radula, inject poison into
prey
• nudibranches can store/use nematocysts from Cnidarians eaten
• have rudimentary lungs
• terrestrial forms evolved lung under mantle
• some water forms have lung and come to surface to breath
cone shell
whelk
nudibranch
Phylum:
Mollusks
Class: Bivalva
(clams, scallops, mussels, oysters)
• bivalve = 2 shells (L/R)
• shells hinged together dorsally by a ligament
• paired adductor muscles contract to close shells
• we eat scallop adductor muscles!
• mantle secretes shell
• shell begins as umbo on larva
• grows with animal
• concentric growth rings
• mantle
• membrane that envelops internal organs (visceral mass)
Phylum:
Mollusks
Class: Bivalva
(clams, scallops, mussels, oysters)
•pair of siphons
•incurrent and excurrent
•maintain stream of water moving in/out of animal
•aids in respiration, feeding, excretion
•respiratory system
•paired gills
•one on each side of visceral mass
•circulatory system
•heart with open circulatory system
Phylum:
Mollusks
Class: Bivalva
(clams, scallops, mussels, oysters)
•lack distinct heads, radulas and tentacles
•locomotion
•large foot adapted for locomotion and anchoring
•most are sessile
•scallops are motile
•sessile filter feeders with palps (folds with cilia on either side
of the mouth) that aid in the handling of food particles
•reproduction- separate sexes, fertilization usually external
•scallops are mobile forms, abundant in marine and
freshwater habitats, part of scallop eaten is adductor muscle
Phylum:
Class:
Bivalva (clams, scallops, mussels,
Mollusks
oysters)
Phylum:
Mollusks
Class:
Cephalopoda (octopus, squid, nautilus)
• most intelligent of mollusks
• predators that compete successfully with fish
• can learn complex tasks
• feeding
• eat fish, mollusks, crustaceans, worms
• foot evolved into series of tentacles w/ suction
cups/hooks to seize prey
• paired jaws, radula
Phylum:
Mollusks
Class: Cephalopoda (octopus, squid, nautilus)
•nervous system
•highly developed w/ brain
•rapid responses via giant nerve fibers attached to
mantle
•elaborate eyes w/ retina similar to vertebrate
•circulatory system
•closed with auxiliary hearts
•shells
•no external shells (except for a few nautilus species)
•squids, cuttlefish- internal remnant of shell that
provides stiffening support
Phylum:
Mollusks
Class: Cephalopoda (octopus, squid, nautilus)
•locomotion
•quick moving
•take water into mantle, expel it through siphon for
propulsion
•also for gas exchange via gills
•eject water violently if threatened
•tentacles
•reproduction
•sexes separate
The Table for Mollusca
Symmetry: bilateral; 3 main body parts (head-foot, visceral
mass, mantle); most secrete hard protective shell; gastropods
show torsion in adult
Segmentation: no
Mesoderm present: yes, triploblastic
Type of body cavity: coelomate; coelom = pericardial cavity in
adult
Ciliated larva: yes, trocophore
Protostome: yes
Cleavage/cells: determinate
The Table for Mollusca
Nervous system: ganglia & sensory structures in head region,
nerve cords; Cephalopods more advanced w/ highly developed
brain & complex eyes
Respiratory system: gills for gas exchange, rudimentary lungs in
some gastropods
Digestive system: complete, one-way; digestive tract in visceral
mass; heterotrophs
Excretory system: nephridia > nephrostome > bladder >
excretory pore
Reproductive system: most have separate sexes, some snails
hermaphrodites, gonads in visceral mass, most go through freeswimming larval stage (trochophore) but in terrestrial mollusks
this stage completed inside egg
The Table for Mollusca
Circulatory system: most have heart with open circulatory
system that pumps the fluid hemolymph around the body;
cephalopods more complex w/ a closed circulatory system and
multiple hearts
Members: Chitons, Bivalves (clams, scallops, mussels),
Cephalopods (octopi, squid), Gastropods (snails, slugs)
Habitat: most marine, some freshwater, some snails and slugs
are terrestrial
Relationship to other phyla: N/A