MARINE WORMS
Common Characteristics of All
Worm Phyla
• Hydrostatic skeleton
• Bilateral symmetry
Phylum Platyhelminthes Flatworms
• Dorsoventrally flattened – flat backs and
bellies
• Have real organs and organ systems
• Ladderlike nerve cord with a simple brain
• Saclike digestive system (only one opening)
• 15,000 species
– Turbellarians – mostly free swimming carnivores
– Flukes (trematodes) – all are parasites
– Tapeworms (cestodes) – parasites with long
segmented bodies
Phylum Nemertea – Ribbon
Worms
• Long flattened bodies
• Complete digestive tract (separate mouth and
anus)
• Circulatory system with blood
• Proboscis – long fleshy tube used to entangle
prey
• 900 species, mostly marine
Phylum Nematoda Roundworms
• Common in sediments or as parasites
• Cylindrical body typically pointed at both
ends
• Complete digestive tract
• 10,000-15,000 species but many could yet
to be discovered
Phylum Annelida – Segmented
worms
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13,000 species
Complete digestive tract
Efficient crawlers and burrowers
Closed circulatory system – blood always remains
in blood vessels (arteries, veins, capillaries)
• Class Polychaeta
– On each segment they have a pair of parapodia and
setae (bristles)
– Gills for respiration
– 6000 species almost entirely marine
– 4 to 10 cm in length
– Deposit or suspension feeders
– Some are tube dwelling
• Class Hirudinea – Leeches
– Mostly freshwater
– Suckers at each end
– No parapodia
Other Marine Worms
• Phylum Sipuncula – Peanut worms
– Peanut shaped, deposit feeders
• Phylum Echiura
– Sausage shape, buried in mud
• Phylum Pogonophora – Beard Worms
– Lack a digestive system, symbiotic relationship
with bacteria for obtaining nutrients
• Vestimentiferans found at hydrothermal vents
• Phylum Chaetognatha – Arrow Worms
– 60 species, but common in plankton, fishlike
body, voracious carnivores