Worms
Chapters 26.3, 26.4, and 27.2
Animal Classification
Animals
Invertebrates
Vertebrates
SpongesCnidariansWormsMollusksArthropodsEchinoderms
Ectotherms(cold-blooded)
Endotherms(warm-blooded)
FishesAmphibiansReptiles
BirdsMammals
Worms
- Phylum Platyhelimenthes- Phylum Nematoda- Phylum Annelida
Flatworms
Phylum Platyhelimenthes (Greek) platy = flat helmins = worm
The least complex worm Acoelomates About 14,500 species exist found in marine,
freshwater, and land The most commonly studied flatworm is the
planarian
Nervous Control
Most of the nervous system is located in its head
The nervous system consists of two nerve cords that run the length of the body
Nerve cords
Nervous Control
Eyespots can detect the presence or absence of light
Sensory cells can detect chemicals and movement in water
Eyespots
Sensory cells
Sensory cells
Nervous Control
Ganglion A small swelling of the nerve cord Receives messages from the eyespots and
sensory pits, then communicates with the rest of the body
Ganglia
Reproduction
Most flatworms are hermaphroditic Can reproduce sexually and asexually Sexual reproduction
Two planarians will exchange sperm Internal fertilization occurs Zygotes are then released in water where they will
hatch
Reproduction
Asexual reproduction Planarians can regenerate when damaged
Regeneration – The replacement or regrowth of missing body parts
Feeding and Digestion in Planarians A planarian feeds on dead or slow-moving
organisms Planarians are not parasitic
To eat, a planarian extends its pharynx from its mouth Pharynx – a tube-like, muscular organ (also
known as the throat)
Extended pharynx
Feeding and Digestion in Planarians Enzymes breakdown the food outside the
body, and then food particles are sucked into the digestive tract
Food is digested in individual cells Waste leaves through its one opening
(mouth)
Feeding and Digestion in Planarians Excretory system – eliminates waste from the
body Flame cells – excess water is removed from
the body
Feeding and Digestion in Parasitic Flatworms Parasitic flatworms
have mouthparts with hooks that keep them attached to their hosts
Hook
Sucker
Feeding and Digestion in Parasitic Flatworms Parasitic flatworms
don’t need a digestive system because they obtain nutrients from food that has been digested by their host
Hook
Sucker
Tapeworm
Scolex – a knob-shaped head
Proglottid – detachable, individual sections that contain muscles, nerves, flame cells, and reproductive organs
Hook
Sucker
Tapeworm
Each proglottid can contain up to 100,000 eggs
Can reach up to 33 ft in length and contain over 2,000 proglottids
Hook
Sucker
The larva will enter the snail host for further development
Adult flukes
First larval stage are found in water
Second larval stage
Eggs are passed out the intestinesFluke larva can bore
through the skin, enter the bloodstream, and move to the intestines
Embryo develops in human waste
Roundworms
Phylum Nematoda Greek word nema = thread
Found in soil, animal, freshwater, and marine environments
More than 12,000 species exist Nearly all plant and animals are affected by
parasitic roundworms
Pseudocoelomates Have a complete digestive system with two
openings (mouth and anus) Free-living species have well-developed
eyespots whereas parasitic species have underdeveloped eyespots
Roundworm Parasites of Humans Ascaris is the most common roundworm
infection in humans worldwide More common in subtropical areas Children become infected more often than
adults Timmy plays in a sandbox…
Roundworm Parasites of Humans Pinworms are the most common roundworm
parasites in the U.S. Children are the commonly infected Eggs can survive two weeks on the surfaces
Roundworm Parasites of Humans During night, female pinworms lay eggs
around the anus of host Taping the anus before bedtime is one
method used to eliminate pinworms
Roundworm Parasites of Humans Trichinella can be ingested in raw or
undercooked pork or wild game (turkey) Trichinella can be controlled by properly
cooking meat
Roundworm Parasites of Humans Hookworms are common in warm climates
where they walk on contaminated soil in bare feet
Hookworms cause people to feel weak and tired due to blood loss
Roundworm Parasites of Humans Hookworm infection from dogs and cats