Coelomates:
Mollusks and
Annelids
Coelomates (Eucoelomates)
• Have body cavity
• Peritoneum present: from mesoderm
Phylum Mollusca (mollusks)
• Large: 110,000 described species (#2 behind
arthropods!)
• Bilateral symmetry, _____________
• Body usually has calcareous shell, muscular foot,
head.
Phylum Mollusca (mollusks)
• Mantle: fold of tissue that wraps around body.
– Secretes shell
– Gills are specialized mantle portion to extract oxygen from
water
• Organs: stomach, heart, gills, etc.
Phylum Mollusca (mollusks)
• Often have radula in mouth
• Usually ____________
Radula
Phylum Mollusca (mollusks)
• Circulatory system open. Heart 3 chambers (2 collect
blood from gills, one pumps to body)
• Coelom is cavity around heart.
Phylum Mollusca (mollusks)
• Excretory system: ____________ gather nitrogenous
wastes from coelom, discharge them into mantle cavity.
Can reabsorb valuable solutes so they aren’t lost
Phylum Mollusca (mollusks)
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Class Bivalvia (bivalves)
Class Gastropoda (gastropods)
Class Polyplacophora (chitons)
Class Cephalopoda (cephalopods)
Class Bivalvia (bivalves)
• Body contained between 2 hinged shells (valves)
• Foot hatchet-like, modified for burrowing in
sand/mud
• Little cephalization: no head, no ___________
Class Bivalvia (bivalves)
• Adductor muscles (2 in most bivalves) close
_____________
• Cilia on gills pull water into and out of shell
through siphons. Brings oxygen, food particles
Class Bivalvia (bivalves)
• Importance:
– 1) biodiversity
– Ex, freshwater mussels. Many Alabama species
endangered, some extinct
– Used to be harvested to make buttons from shells
Class Bivalvia (bivalves)
• Importance:
– Larvae parasitic on host fish gills or fins as glochidia
– How get fish to come close to receive glochidia?
Class Bivalvia (bivalves)
• Importance:
– Lure them in!
– Mantle of female mussel mimics fish.
Class Bivalvia (bivalves)
• Importance:
– 2) pollution monitors
– Aquatic filter feeders (mussels) process large quantities of
water during feeding
– Concentrate metals, pesticides, PCBs.
– Sample tissues periodically to detect pollution
– California Mussel Watch Program, National Mussel Watch
Program.
Class Bivalvia (bivalves)
• Importance:
– 3) human food (clams, oysters, scallops, mussels)
oysters
clams
mussels
Class Bivalvia (bivalves)
• Importance:
– 3) human food (clams, oysters, scallops, mussels)
Scallops have one large
(edible) adductor muscle
Class Bivalvia (bivalves)
• Importance:
– 4) jewelry (pearls)
Class Bivalvia (bivalves)
• Importance:
– 5) invasive species. Ex, zebra mussel from Caspian
Sea
– Colonies encrust exposed surfaces (mussels are filter
feeders)
– Can kill freshwater clams (wiped them out in Lake
Erie)
Class Bivalvia (bivalves)
• Importance:
– 5) invasive species.
– Cleaning water intake pipes will cost $3.1 billion
over next 10 yr.
Class Polyplacophora (chitons)
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Small group: 600 species
Marine, rocky intertidal zone
Graze algae from rocks
Have 8 overlapping valves
Cling to rocks with foot.
Gumboot chiton:
largest in world
Class Gastropoda
(snails/slugs/limpets)
• Single shell present (usually coiled in snails) or
lacking (slugs)
• Foot flattened, modified for crawling
• Head with eyes, tentacles
• Radula modified as _________ (many herbivores,
some predators)
Rare snails
• Land snails diverse
group
• On islands, have radiated
into many species
• Ex, Partulid snails from
S. Pacific.
Rare snails
• 120 species in family
Partulidae
• Moorea, small S.
Pacific island.
Rare snails
• Moorea had 7 species of Partulid snails found
nowhere else on Earth.
Rare snails
• Problem: Giant African snail introduced to
island
• Damaged agriculture.
Rare snails
• Solution (new Problem):
Introduce predatory
Euglandina snail
• Wasn’t supposed to
invade areas containing
Partulid snails and eat
them
• But it did.
Rare snails
• By 1987 all Partulid
snails on Moorea were
extinct in wild
• But 6 of 7 species are
being maintained in
captivity by several
zoos.
Rare snails
• Ex, white abalone
• Marine snail, coast S. California.
lives on submerged rocks, eats
algae. Has large foot which is
delicious.
Shells of red
abalone
Rare snails
• Ex, white abalone
• Fishery developed in 1970s, when populations
were 1,000-5,000/acre
• Quickly overharvested them
• Now <1 abalone/acre left (maybe 1,600 total)
• Listed endangered 2001
Rare snails
• Ex, white abalone
• Problem: Don’t move about much. Depend on
water to mix sperm and eggs. Males/females must
be about 3 feet apart for fertilization to occur!
• Density now too low for reproduction in wild
• Captive breeding program underway.
Female releasing eggs
(can make 3 million!
Other uses of snail shells
• Seashell collectors
This rare specimen is for sale: $7,000
Other uses of snail shells
• Shell money:
early form of
currency
(before coins)
S. Pacific
shell money
Sumerian shell ring money:
Syria 3000BC
Class Gastropoda (snails/slugs)
• Nudibranchs (naked gills)
• ____________. Some can eat
cnidarians and transfer
nematocysts to their gills to
defend them from enemies!
QuickTi me™ a nd a Cinep ak decompre ssor are n eede d to see thi s pi ctu re.
Class Cephalopoda
• Foot divided into arms/tentacles
– Squids: 10 tentacles. Octopuses
and cuttlefish: 8. Nautiluses: 80-90.
• Tentacles with suckers
Class Cephalopoda (octopuses,
squids, nautilus)
• Have ______________
• Have extreme cephalization
• Shell absent (octopus, squid), internal (cuttlefish:
cuttlebone), or present (nautilus)
• Swim by taking water into mantle cavity and
expelling it through siphon (jet propulsion)
Class Cephalopoda
• Excellent vision
• Intelligent
• Have both long-term
and short-term
memory
• Ex, one aquarium
octopus helps clean
its aquarium by
handing debris to staff
Common octopus
Class Cephalopoda
• Deadly (Octopussy)
• Blue-ringed octopus: bite deadly
due to tetrodotoxin (neurotoxin)
• No known antidote
• Fashionable pet in Thailand.
Phylum Annelida (segmented worms)
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11,000 species (2/3 marine)
Bilaterial symmetry, triploblastic
Protostomes
Eucoelomates: Coelom fluid-filled and
pressurized. Provides hydrostatic skeleton
Phylum Annelida (segmented worms)
• Note circular and longitudinal muscles
• Cephalization, complete digestive tract
Phylum Annelida (segmented worms)
• Closed circulation system (arteries, veins,
capillaries). Note dorsal and ventral blood
vessels. Dorsal moves blood to head, ventral
toward tail. Multiple ____________.
Phylum Annelida (segmented worms)
• Excretory system: metanephridia
• Bristles (setae) on body. Sensory or aid in
locomotion
Phylum Annelida (segmented worms)
• Monoecious. Gonads: where sperms and eggs
made
• Worms mate by passing sperm to each other
Mating Earthworms
Phylum Annelida (segmented worms)
• Clitellum located near reproductive organs
• Clitellum secretes ___________.
• Sheath collects eggs/sperm as it slides off worm
to form cocoon
• Young worms develop in cocoon.
Earthworm cocoons and
head of pin
Phylum Annelida (segmented worms)
• Segmented body: Key characteristic. Body series of
compartments with similar systems in each
• Advantages
– 1) Allows adjacent segments to operate independently, give
precise control of body movement (expand and contract
segments)
– 2) System redundancy: if one segment injured, others contain
muscles, nerves, excretory, circulatory systems that can
continue to function.
QuickTi me™ a nd a Cinep ak decompre ssor are n eede d to see thi s pi ctu re.
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Class Oligochaeta (earthworms)
Most familiar group
Few setae, head poorly developed
Cuticle outside epidermis
Detritivores: Feed on organic
matter in soil. Castings rich in
minerals.
• Burrowing causes soil aeration
• Flooding rains can drown them
Large Australian
earthworm
Class Polychaeta (polychaetes)
• Marine. Most species in this class. Important members of
marine ecosystems.
• Parapodia (paddle-like appendages) present with setae
on them
• Head well-developed. Usually dioecious, ____________
external
Class Polychaeta (polychaetes)
• Examples in lab: plume worm, clam worm
Clam worm
Plume worm (lives in tube)
Filters water for food with
tentacles
Class Hirudinea (leeches)
• 1 or 2 suckers present: anterior (head end) and posterior
(tail end)
• No setae or _______________
• No septa between segments (superficial segmentation:
not segmented within body)
Class Hirudinea (leeches)
• Parasites or predators. Mostly freshwater.
• Parasites: Asian ones terrestrial (tropics). Detect heat and
vibrations
• Others aquatic.
Class Hirudinea (leeches)
• Parasites: have anticoagulant (so blood doesn’t clot) and
anesthetic (so leech not noticed) in saliva
• Medical use: can relieve inflammation and swelling
better than medication
Lophophorates
• 3 marine phyla with special feature: ________________
• Lophophore: Circular or U-shaped ridge around mouth,
bearing 1 or 2 rows of hollow ciliated tentacles
• Cilia trap detritus/plankton (filter feeders) and tentacles
aid in gas exchange
• Have mix of protostome and deuterostome features
(classification uncertain)
Lophophorates
• Phylum Phoronida (phoronids)
– Live in tube. Feed with tentacles.
– Have U-shaped gut
– Only 10 species
Lophophorates
• Phylum Ectoprocta (bryozoans)
– Like small phoronids (U-shaped gut). Marine and freshwater.
4000 species
– Live in colonies. Produce ____________: chitinous chamber
that connects colony members.
Lophophorates
• Phylum Brachiopoda (brachiopods)
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Have 2 calcified ______________ (look like clams)
Attach valves to substrate with pedicel
Open valves to feed with lophophore
300 species now. Cold water marine.
Lophophorates
• Phylum Brachiopoda (brachiopods)
– Big fossil record (30,000 species described)
– Dominant in Paleozoic Era (543-248 million years ago)
– Useful fossils for dating sediments or characterizing ocean
conditions in past
Phylum Arthropoda
(arthropods)
Phylum Arthropoda (arthropods)
• Most successful of all animal phyla
• Everywhere: Terrestrial, aquatic
Phylum Arthropoda (arthropods)
• Huge group: 70%
of all named
animal species. At
least 1,000,000.
• 80% of arthropods
are insects (Class
Insecta), and 50%
of insects are
beetles (Order
Coleoptera)
Phylum Arthropoda (arthropods)
• Closely related to annelids
Phylum Arthropoda (arthropods)
• General characteristics:
– 1) Eucoelomates, bilateral symmetry, ___________
Phylum Arthropoda (arthropods)
• General characteristics:
– 2) Body segmented. Ancestral trait is many ________
segments. In derived groups, segments fused into
functional units (tagmata).
– Regions: head, thorax, abdomen. If head and thorax
are fused, called cephalothorax
Phylum Arthropoda (arthropods)
• General characteristics:
– 3) Extreme cephalization (head with many sense
organs). Example: compound eye. Made of
ommatidia (each a single eye with ________). May
also have simple eyes (ocelli) with single lenses.
Phylum Arthropoda (arthropods)
• General characteristics:
– 3) Compound eyes see the world in a different way
– Advantage: detection of motion.
Phylum Arthropoda (arthropods)
• General characteristics:
– 4) Innovation: Have exoskeleton; hard coating of ________
on outside of body
– Secreted by epidermis. Protects against enemies, water loss
(on land). Provides attachment points for muscles and organs
Phylum Arthropoda (arthropods)
• General characteristics:
– Problem: can’t grow. Must be shed during molting.
– Problem: will not support large body volume efficiently.
Larger body has much greater surface area. Keeps
arthropods ______________
Softshell blue crab
in the making...
Phylum Arthropoda (arthropods)
• General characteristics:
– 5) Innovation: Have jointed appendages (legs, antennae,
mouthparts) “arthros” (Gr.)=jointed. “podes” (Gr.)=feet
– 2 types. Biramous have 2 branches, uniramous have 1
branch
Phylum Arthropoda (arthropods)
• General characteristics:
– 6) Circulatory system open. Heart pumps blood toward head,
then flows back through body
Phylum Arthropoda (arthropods)
• General characteristics:
– 7) Nervous system. Brain small. Ventral ganglia control
many body activities
Phylum Arthropoda (arthropods)
• General characteristics:
– 8) Respiratory system
– Terrestrial: Most have spiracles, which open into tracheae
that branch into ______________
– Some (ex, spiders) have book lungs, leaflike plates in
chamber
– Aquatic: gills
Phylum Arthropoda (arthropods)
• General characteristics:
– 9) Excretory system
– Varied. Malphigian tubules bathed in blood, collect fluid,
dump wastes in hindgut. Reabsorb water and salts in hindgut