Worms and Mollusks

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Worms and Mollusks

• Chapter 27

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PhylumPlatyhelminthes (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 animals
• Dead animals
• Single opening to function as a mouth and anus.
• Possess a pharynx

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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 animals
• No skeletal,circulatory,or respiratory system

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Planarians continued

• Small brain with two nerve cords
• Hermaphrodites
• Internal fertilization
• Can also reproduce asexually.

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Parasitic flukes (c. Trematoda)

• Usually two or more hosts. (Page 687)
• Primary host human (site of asexual
  reproduction)
• Causes the disease schistosomiasis

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Tapeworms (c. Cestoda)

• Parasites. Example beef tapeworm
• Head 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 bodies
• Often covered with a thick cuticle
• 1 mm to 1 meter in length
• Both free-living and parasitic
• 2 body openings
• Major difference from the flatworms
• Food 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 worm

• Causes trichinosis
• Often 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

• Thoroughly cook pork products
• Feed hogs uncontaminated feed
• 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

• PINWORMS
• Most common nematode infection in N. America
• Especially infants and toddlers.

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HOOKWORMS

• Often will enter through the feet.
• Common in areas where sewage disposal is
  inadequate

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Phylum Annelida

• Also 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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more annelid facts

• tube within a tube body plan.
• Closed circulatory system, 2 openings

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respiration

• Aquatic annelids breathe using gills
• Land-dwelling annelids breathe through the skin

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excretion

• Nephridia excretory organs that filter
  nitrogenous waste in the ceolom.

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Reproduction

• Hermaphroditic. eggs and sperm released at the
  clitellum

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Earthworms

• C. Oligochaeta
• First segment prostomium
• Setae 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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Ecology of Earthworms

• Help to aerate the soil
• Provide nutrients in to the soil in fecal matter
• Participate in a wide range of food chains

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Leeches

• Mainly freshwater.
• Suckers on both ends of body
• Saliva 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 Mollusca

• Second largest phyla of animals after the
  arthropods.
• Found in fresh water, salt water, and on land
• ex.

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Mollusk characteristics

• Soft bodies, 3 cell tissue layers
• Many are used for food and jewelry
• Possess 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. bivalves

• 2 parts to their shells.
• Strong adductor muscles to keep the shell closed
• Incurrent siphon carries water and food into
  the mantle cavity
• Excurrent siphon siphon where water is expelled.

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Examples of bivalves
clams and mussels
scallops
oysters
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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 sexes
• Sperm is released by the excurrent siphon and
  enters a female via the incurrent siphon where
  fertilization takes place.

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2. gastropods

• Largest class of mollusks
• Most possess a single shell.exception slug

slugs
conch
snails
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3. cephalopods

• Most advanced mollusks
• All are marine predators
• Use tentacles to gather and manipulate food
• Can swim rapidly by expelling a jet of water from
  their mantle cavity.
• Some may discharge an inky fluid for defense
• Octopus (8 arms) squid (10 tentacles)

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examples
nautilus
cuttlefish
octopus
squid