Invertebrates

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Invertebrates

• Flatworms, Roundworms, Mollusks and Annelids

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Phylum Platyhelminthes - Flatworms

• Acoelomate animals with bilateral symmetry
• Class Cestoda parasitic flatworms
• tapeworms
• Class Trematoda- flukes, also parasitic
• Class Turbellaria- planarians, not parasitic
• Marine and fresh water
• Free living
• Do not cause diseases

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Feeding and Digestion

• Feed on dead or slow prey
• Uses a muscular organ called the pharynx which it
  extends out from the middle of its body.
• It begins to digest food outside the body
• Sucks up the food into the gastrovascular cavity
• Phagocytosis brings the food into individual
  cells where it is digested

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Sensory response

• Some have nerve net
• Others have beginnings of a central nervous
  system
• Two nerve cords run the length of its body
• Sensory pits that detect chemicals
• Eyespots that detect light
• Ganglion at anterior of nerve cord receive
  messages from the eyespots and sensory pits
• Messages can be sent from nerve cord to muscle
  cells

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Reproduction

• Most flatworms hermaphroditic
• Internal fertilization, planarians exchange sperm
• Reproduce asexually
• Regeneration replacement or regrowth of missing
  body parts through mitosis
• If a planarian is torn in half, the tail will
  grow a head and the head will grow a tail

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Schistosomiasis

• Parasitic flatworm with a two host life cycle
• Fluke that embeds itself in human intestine
• Eggs pass out of body with human waste
• Eggs hatch enter a snail host where they
  reproduce and then leave the snail
• When humans walk in the water the worms bore
  through the skin, make their way to the intestine
  and the cycle starts over.

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Phylum Nematoda the roundworms

• Pseudoceolomate, body cavity partly lined with
  mesoderm.
• Simples animal with digestive tract with two
  openings.
• Live in soil, animals, fresh and marine
  environments.
• Some free living others parasitic
• Tapered at both ends have thick outer covering
  that protects them from being digested
• About half of them are parasitic

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Human roundworm parasites

• Ascaris infects children who swallow them
• Hook worms enter through bare feet that walk on
  them
• Pin worms most common in children
• Trichinella worms that cause trichinosis
• Enter the body in undercooked pork
• Cook thoroughly to kill the worms

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Plant parasites

• Nematodes infect pine trees, cereal crops, potato
  plants
• Cause cysts on roots, interferes with water uptake

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Phylum Mollusca soft bodied

• Large phylum, very diverse
• Three common classes
• Bivalvia two shelled valves
• Marine and fresh water
• Clams, oysters, scallops
• Gastropoda- stomach foot
• Fresh, marine and terrestrial varieties
• Snails, whelks, slugs, marine slugs (nudibranchs)
• Cephalopoda- head foot
• Only marine
• Octopus, squid, nautilus

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All mollusks share many similarities

• Bilateral symmetry
• First organism with coelom developed within the
  mesoderm
• Non segmented body
• Muscular foot for movement
• A mantle that surrounds the internal organs in
  shelled mollusks it secretes the shell
• Visceral mass that contains the internal organs
• Organ systems for excretion, circulation,
  respiration, digestion and reproduction
• Many mollusks have one or two shells
• All but bivalves have a radula

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The clam class bivalvia

• Shells are hinged, the body of the clam is
  between
• Nephridia- structures that form the excretory
  system
• Two siphons at the edge of the mantle let water
  in and out of clam. Incurrent siphons take water
  with food particles and oxygen move over the
  gills, excurrent siphons expel the water and
  wastes
• Adductor muscles hold the valves of the clam
  together
• The foot is used for movement

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Respiration, Circulation and Excretion

• Gills are part of the mantle. Filamentous
  projections increase surface area for efficient
  gas exchange
• Land snails have primitive lung
• Sea snails use diffusion
• Three chambered heart, open circulatory system.
• Heart pumps blood through vessels into open
  spaces, bringing oxygen and removing wastes.
• cephalopods have closed circulatory system.
• Excretory structures called nephridia that
  collect wastes from coelom the gills expel the
  wastes

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Food gathering

• Bivalves are filter feeders
• Take in food in water by the incurrent siphons
• Gastropods and Cephalopods are predators The
  radula located within the mouths of gastropods
  and cephalopods, has rows of tooth-like
  structures that rasp, scrape and cut food

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Reproduction and nervous system

• Most mollusks have separate sexes
• Eggs and sperm are released at the same time
  fertilization taking place in the water
• Land dwellers are hermaphrodites
• Clams do not have a head region, they have simple
  nervous system with a nerve ganglion above their
  foot that serves a simple brain
• Cephalopods have complex brains with eyes

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Phylum Annelida segmented worms

• Phylum includes earthworms, leaches, bristle
  worms
• Bilateral symmetry
• Coelomate.
• Organ systems
• Two body openings, mouth, anus
• Body plan has a tube within a tube, both lined
  with mesoderm. The internal tube is the digestive
  tract.
• Internal body walls called septa separate
  segments
• Nerve cord that is located on ventral side
• Setae are tiny bristles on each segment
• Anchor body so that each segment can move along
  ground.
• Parapodia some have these fleshy appendages
• Live in fresh water, marine and terrestrial
  environments

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Segmentation

• Their cylindrical bodies divided into ringed
  segments, each segment has its own muscles so
  that each segment can shorten and lengthen.
• All coelomate animals except for mollusks are
  segmented
• Marine segmented worms are Class Polychaeta. Have
  parapodia and many setae
• Earthworms are Class Oligochaeta have no
  parapodia and few setae
• Leaches, Class Hirundinea, lack setae and
  parapodia

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Earthworms- Class Oligochaeta
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• Respiration gas exchange through diffusion
• Digestion digestive tract, mouth takes up food,
  passes to pharynx then esophagus to crop and
  gizzard where soil is ground up and organic
  nutrients are passed to intestine and absorbed
  into the bloodstream. The waste matter passes out
  through anus, called castings, they fertilize
  soil.