Transcript Worm-like Animals

Worm-like Animals
Characteristics
• Invertebrates.
• Cephalization.
– Sense organs and nerve cells located at anterior end.
• Coelom.
Characteristics
Phylum Platyhelminthes
“Flatworms”
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Flattened with no coelom.
Unsegmented.
No circulatory or respiratory system.
Digestive cavity with one opening.
Mostly parasitic.
1 mm to 5 m in length.
Phylum Platyhelminthes
Class Cestoda
• Parasitic tapeworms.
• Suckers and hooks attach tapeworm to
intestines.
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Phylum Nematoda
“Roundworms”
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Unsegmented cylindrical bodies.
Pseudocoelom.
Complete digestive tract.
No circulatory or respiratory system.
Mostly parasitic.
2 mm to 2 m in length.
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Phylum Nematoda
Phylum Annelida
“Segmented Worms”
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Segmented bodies.
Presence of a coelom.
Complete digestive tract.
Has a circulatory
system.
• Gas exchange via
gills or skin.
Phylum Annelida
• Many have bristles on outer surface to aid
with movement.
• 0.5 mm to 3 m in length.
• E.g., Earthworms and leeches.
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Phylum Mollusca
Characteristics
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Soft-bodied.
Coelom.
Two body openings.
Bilateral symmetry.
Body Plan
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Three unsegmented body parts:
1. Foot:
• Locomotion and feeding.
2. Mantle:
• Wraps around body and secretes shell.
• In some, shell may be reduced or absent.
3. Visceral Mass:
• Internal Organs.
Body Plan
Body Plan
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Complete digestive and circulatory
system.
Gills for respiration.
<1 cm to 20 m
in length.
Class Bivalva
• E.g., clams, oysters, scallops & mussels.
• Hinge connects two shells.
• Primarily sessile.
– Foot may be modified
to burrow.
• No head.
• Filter feeders.
• 0.5 mm to 1.4 m in size.
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Class Gastropoda
• E.g., snails and slugs.
• Foot used for locomotion.
• Respiration through gills and
moist skin.
• Spiral shell except for slugs.
• 0.5 mm to 75 cm in size.
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Class Cephalopoda
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E.g., squids and octopi.
Shell reduced to internal rod.
Only mollusk with closed circulatory system.
Tentacles with suckers.
Well-developed brains; capable of learning.
Move via jet propulsion (by funnel).
10 mm to 20 m in size.
Class Cephalopoda
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Phylum Echinodermata
Phylum Echinodermata
• E.g., sea stars, sea urchins, sand dollars and
sea cucumbers.
• Larvae: Bilaterally symmetrical.
• Adults: Radially symmetrical around 5+ arms.
Phylum Echinodermata
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Complete digestive system.
Simple circulatory and nervous system.
No respiratory or excretory system.
No head.
Endoskeleton
with spiny
projections.
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