Worms and Mollusks
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Transcript of Worms and Mollusks
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Worms and Mollusks
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Phylum:Platyhelminthes
(flat) (worm) Simplest bilateral symmetric animals showing a head and tail region.
3 layers: endoderm, ectoderm, mesoderm
Known as acoelomates (without a coelom)
coelom : a fluid-filled body cavity
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General body structure:
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Feeding
Free-living flatworms can eat:Tiny aquatic animalsDead animalsSingle opening to function as a mouth and
anus.Possess a pharynx which is used to eat
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Respiration, circulation, excretion
Breath through diffusion
Flame cells: specialized cells used for removing excess water.
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Planarians (c. Turbellaria)
Free-living freshwater flatworm.Possess a digestive tract, mouth,
pharynx, and branched intestine.Feed on small microscopic animalsNo skeletal,circulatory,or
respiratory system
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Planarians continued
Small brain with two nerve cords
HermaphroditesInternal
fertilizationCan also
reproduce asexually.
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Marine Flatworms polycadiaStrange mating behaviorBeautiful colors
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Parasitic flukes (c. Trematoda)Usually two or
more hosts. Primary host:
human (site of asexual reproduction)
Causes the disease schistosomiasis
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Tapeworms (c. Cestoda)
Parasites. Example: beef tapewormHead region (scolex) : contains suckers and
hooks used to attach to a host organism.Proglottids : square body segments used for
reproduction
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Phylum: Nematoda (roundworms)
Long cylindrical bodiesOften covered with a thick cuticle1 mm to 1 meter in lengthBoth free-living and parasitic*** 2 body openings***
Major difference from the flatwormsFood and wastes will NOT be mixed
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Form and function
Eat small animals, bacteria, algae, fungi, etc
Exchange gases through diffusion Possess a simple nervous system Move through contracting muscles Reproduce sexually
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Trichina wormCauses trichinosisOften present in pigs. Grow to about one
millimeter in length and become cysts in pig muscles.
People eat contaminated pork and larval cysts develop into adults in human intestines.
New larvae can end up in human muscles.
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Ways to prevent trichinosis:
1. Thoroughly cook pork products2. Feed hogs uncontaminated feed3. Freeze pork immediately after packaging
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Filaria Roundworm that
causes the disease elephantiasis.
Carried by mosquitoes Infects bloodstream
and blocks lymph nodes resulting in severe swelling.
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Ascarid worms
Affects more than 1 billion people
Affect people, horses, pigs, chicken, cattle, dogs, cats etc.
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Pinworms and Hookworms
PINWORMSMost common nematode infection in N. AmericaEspecially infants and toddlers.
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HOOKWORMSOften will enter
through the feet.Common in areas
where sewage disposal is inadequate
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Phylum: AnnelidaAlso known as the segmented worms.The body is divided into separate body
segments.Marine,fresh water,and on land.Parasitic and free-living. ex.
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Annelida Characteristics Characteristics of Annelida:-
1)Bilaterally symmetrical.
2)Body has more than two cell layers, tissues and organs.
3)Body cavity is a true coelom.
4)Body possesses a through gut with mouth and anus.
5)Body has 3 separate sections, a prosomium, a trunk and a pygidium.
6)Has a nervous system with an anterior nerve ring, ganglia and a ventral nerve chord.
7)Has a true closed circulatory system.
8)Has no true respiratory organs.
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…more annelid facts“tube within a tube” body plan.Closed circulatory system, 2 openings
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respirationAquatic annelids breathe using gillsLand-dwelling annelids breathe through the
skin
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excretionNephridia : excretory organs
that filter nitrogenous waste in the ceolom.
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ReproductionHermaphroditic. eggs and sperm released at
the clitellum
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Marine Annelids
Class Polychaeta-means many bristles
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C. OligochaetaFirst segment = prostomiumSetae = small hair-like extensions
on ventral surface used for locomotion.
Possess many “hearts”
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The “hearts” of an earthworm:
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Mainly freshwater.Suckers on both ends of bodySaliva of leeches contain enzymes
that prevent blood from clotting (anticoagulants)
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Leech Anatomy
Attaches to prey with posterior sucker, and uses anterior sucker to “suck” blood.
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Medicinal uses of leeches
Used to be used for “leeching” by early physicians to rid a sick person of “bad” blood.
Still used in surgery to prevent blood clotting and unwanted swelling due to excess blood.
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Phylum: MolluscaSecond largest phyla of animals after the
arthropods.Found in fresh water, salt water, and on landex.
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Mollusk characteristics:
Soft bodies, 3 cell tissue layersMany are used for food and jewelryPossess a foot = large ventral muscle used
for movement.Most have a radula (exception: bivalves)Mantle - fold of skin that surrounds the
body organs
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1. bivalves2 parts to their shells (bi).Strong adductor muscles to keep the shell
closedIncurrent siphon – carries water and food
into the mantle cavityExcurrent siphon – siphon where water is
expelled.
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Examples of bivalves:
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pearls
Mother-of-pearl inner smooth part of bivlave shell.
Made primarily by oysters when a foreign object gets lodged inside between mantle and shell.
Come in many colors
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Reproduction and nutrition
Bivalves are filter-feeders. (plankton and small invertebrates)
Separate sexesSperm is released by the excurrent
siphon and enters a female via the incurrent siphon where fertilization takes place.
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2. gastropodsLargest class of mollusksMost possess a single shell.exception: slug
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3. cephalopodsMost advanced mollusksAll are marine predatorsUse tentacles to gather and manipulate foodCan swim rapidly by expelling a jet of
water from their mantle cavity.Some may discharge an inky fluid for
defenseOctopus (8 arms) squid (10 tentacles)
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examples: