Biology 11 – Kingdom Animalia Study of the Primitive Worms
Phylum Platyhelminthes: Flatworms Phylum Nematoda: Roundworms
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Phylum Platyhelminthes – the Flatworms
The Planarians
The Tapeworms
The Flukes
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Importance of the Flatworms to Evolution
Bilateral body plan – left side mirror image of right Cephalization – development of the head
sense organs and nerves concentrated in head region
Centralization of nervous system:
Nerve cord accompanies cephalization and bilateral symmetry.
Advanced muscle tissue present; Primitive excretory system
allows removal of metabolic wastes
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Phylum Platyhelminthes Characteristics
Bilateral symmetry; anterior and posterior ends.
Body flattened Well developed Epidermis No internal body cavity other than digestive tube (acoelomate)
Parenchyma (connective tissue) fills space between organs.
Still one opening
Incomplete digestive system
This critter eats and poops out of its mouth – mmmm, pass the popcorn
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Flatworm Nervous System and Excretory System Characteristics
Nervous system with ganglia and longitudinal nerve cords and branches
Simple sense organs; eyespots in some.
Excretory system
Lack circulatory, respiratory, and skeletal systems. Reproductive system complex; Well-developed gonads and accessory organs. Free-living (eg Planarians) have well developed digestive and nervous systems to seek-out and process food
Parasitic Tapeworms – rely on host’s digestive system to process food, which absorb. No need for advancement of nervous system – not needed. 316 BIOL Phylum Platyhelminthes 6
Nervous System and Sense Organs
Have a Nerve-net. Most have more complex system. Cerebral ganglion = primitive brain coordinates impulses. “Ladder” system carries impulses throughout body
Many sense organs present Eyespots Chemoreceptors, touch sensors and rheoreceptors (sense direction) also common
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Advantage of Being Flat
Surface area to volume ratio is important for organisms.
3mm
many substances enter and leave through body surface. Faster absorption and release of wastes
3mm
3mm
Volume = 3 x 3 x 3 = 27mm2 Area = 6(3 x 3) = 54mm3 3mm 1mm
9mm
Volume = 9 x 3 x 1 = 27mm2 Area = 2(9 x 1) + 2(3 x 1) + 2(3x9) = 78mm3
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Cross Section of a Flatworm
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Nutrition and Digestion
Typical digestive system includes a mouth, a pharynx, and an intestine.
Parasitic Tapeworms and Flukes lack a digestive system
Free living flatworms (Planarians) are carnivorous; suck prey into pharynx with mouth. Undigested food goes out mouth. Yes, folks, they eat and excrete out the same hole
Parasitic flatworms, such as the Tapeworm absorb molecules from host.
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Reproduction – in Free-living Flatworms such as Planarians
May reproduce sexually or asexually
Asexual: Binary fission – split in two
Sexual: Both sexes present in same flatworm (hermaphrodites).
Fertilization internal, eggs produced
Embryos emerge as juveniles resembling adults.
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Reproduction in theTapeworm!
Lack digestive system
Sucker and hooks on anterior end for attachment
Neck produces new segments Called proglottids Each proglottid contains male and female gonads
Reproductive output high Many proglottids per worm Many eggs per proglottid
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Tapeworm - Life Cycle
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Flukes -- Life Cycle of a Liver Fluke
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The Coelom or Body Cavity Advances
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Another Look at the Coelom
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Roundworms
Phylum Nematoda
Non-segmented; have smooth body wall
Generally colorless, less than 5 cm in length, occur almost everywhere Parasitic roundworms Live anaerobically in every type of animal and many plants Have tube-within-a-tube body plan Digestive tract is complete; has both mouth & anus
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Roundworm Ecological Roles
Carnivores that catch and eat algae, fungi, decaying matter Recyclers Parasites of Plants – eg. The Golden Nematode attacks potato crops, causing severe devastation Parasites of animals -
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Ascaris – Parasitic Roundworm of Pigs and Humans
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Unfortunately, they can Grow quite Big!
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Parasites: Your Pet's Enemies Tiny parasites that pose a gigantic threat
Heart worms inside the dog's heart, can grow to a length of 14". What they do: Restrict blood flow and cause organ damage. Symptoms include coughing. labored breathing, heart failure. Untreated, heart worm disease can kill a dog. Death may occur within 72 hours.
How they spread: Transmitted by over 70 species of mosquitoes. Virtually all dogs are at risk. Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.
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Adult roundworms live in the dog's small intestine.
What they do: Cause diarrhea, vomiting, stunted growth, rough coat, bloated belly.
How they spread: Almost all puppies get roundworms from their mothers. Dogs can also pick up roundworms from the soil. Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.
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Enlarged hook worm mouth showing 'teeth'.
What they do: Attach to the dog's intestinal lining, leaving bleeding internal wounds. Cause blood loss, anemia, and diarrhea. As few as 100 hook worms can kill a puppy. How they spread: Eggs pass through the feces of an infected dog into the soil where they are easily swallowed or can penetrate through a dog's feet. Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.
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Symptoms: Larvae digested enter bloodstream and burrow into organs, causing absolutely horrendous pain and in some cases death.
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Filarial (threadlike worms) are nematodes that may block the passage of Fluids in the Body
Disease: Elephantitis The disease is caused by parasitic worms, including Wuchereria bancrofti, Brugia malayi, and B. timori, all transmitted by mosquitoes. Lymphatic filariasis currently affects 120 million people worldwide, and 40 million
Blocks Lymphatic nodes which drain fluid to and from the blood. Tropics, Africa and Asia
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