Coelomates: Mollusks and Annelids

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)• 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


– Larvae parasitic on host fish gills or fins as glochidia– How get fish to come close to receive glochidia?


– Lure them in!– Mantle of female mussel mimics fish.


– 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.


– 3) human food (clams, oysters, scallops, mussels)

clams

mussels

oysters


– 3) human food (clams, oysters, scallops, mussels)

Scallops have one large(edible) adductor muscle


– 4) jewelry (pearls)


– 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)


– 5) invasive species. – Cleaning water intake pipes will cost $3.1 billion

over next 10 yr.

Class Polyplacophora (chitons)• 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 redabalone


• 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


• 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)

Sumerian shell ring money: Syria 3000BC

S. Pacificshell money

Class Gastropoda (snails/slugs)• Nudibranchs (naked gills)

• ____________. Some can eat cnidarians and transfer nematocysts to their gills to defend them from enemies!

QuickTime™ and aCinepak decompressorare needed to see this picture.

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)• 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.

QuickTime™ and aCinepak decompressorare needed to see this picture.

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 withtentacles

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)

– 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, ___________


– 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


– 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.


– 3) Compound eyes see the world in a different way– Advantage: detection of motion.


– 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


– 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 crabin the making...


– 5) Innovation: Have jointed appendages (legs, antennae, mouthparts) “arthros” (Gr.)=jointed. “podes” (Gr.)=feet

– 2 types. Biramous have 2 branches, uniramous have 1 branch


– 6) Circulatory system open. Heart pumps blood toward head, then flows back through body


– 7) Nervous system. Brain small. Ventral ganglia control many body activities


– 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


– 9) Excretory system

– Varied. Malphigian tubules bathed in blood, collect fluid, dump wastes in hindgut. Reabsorb water and salts in hindgut

Coelomates: Mollusks and Annelids

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