Transcript 6. Phylum - Nematoda

Phylum Nematoda –
Roundworms
ACAD
Body Plan
•Bilateral symmetry
•Long and slender unsegmented body that
tapers at both ends
•Protected by noncellular layer called a
cuticle
•Pseudocoelomates
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Systems
•One-way digestive tract with separate
mouth and anus
•Exchange gases, distribute nutrients, and
excrete metabolic waste via diffusion
through body walls
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Feeding
•Free-living roundworms use grasping
mouthparts and spines to catch and eat
other small animals
•Many others are parasitic
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Reproduction
•Reproduce sexually
•Most species have separate sexes
•Parasitic roundworms often have life cycles that
involve two or three different hosts or several organs
within a single host
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Parasitic Roundworms Groups
Hookworms
•Trichinella – get trichinosis by eating raw or
incompletely cooked pork
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Hookworm Life-cycle
•Eggs hatch and develop in the soil
•Use sharp toothlike plates and hooks to burrow
into the skin and enter the bloodstream
•Travel through the blood of their host to the lungs
and down to the intestines
•Suck the host’s blood, causing weakness and
poor growth
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Filarial Worms
•Transmitted by mosquitoes
•Causes Elephantiasis
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Roundworms and Human Disease
Ascaris –
•serious parasite of humans and many other
vertebrate animals
•absorbs digested food from the host’s small
intestine; makes host very sick
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Ascarids
Ascarids taken from children of one village.
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Pinworms
•Most common roundworm parasite in the United
States – highly infectious
•Do not cause serious disease
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Phylum Rotifera – Rotifers
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Rotifers
•Pseudocoelomates
•Transparent
•Free-living and aquatic
•Have a crown of cilia surrounding their mouth
called a corona
• The beating of the cilia sweeps food through
their mouths into their digestive tract
• Food moves through a one-way digestive
tract as it is digested
•Rotifers are capable of parthenogenesis –
unfertilized eggs hatch into adults (all females)
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