•18.8 Nematodes have a pseudocoelom and a complete digestive tract

– Nematodes (roundworms) make up the phylum Nematoda

• Have a pseudocoelom and a complete digestive tract

• Are covered by a protective cuticle• Are numerous, diverse, and found in most

environments

– Many are free living; others are plant or animal parasites

LE 18-08a

Mouth

– Caenorhabditis elegans, a free-living nematode, is an important organism for genetic research

• The complete genomic sequence has been determined

– Trichinosis is a disease caused by the nematode Trichinella spiralis

• Humans can get this parasite by eating raw pork

LE 18-08b

Muscle tissue Trichinella juvenile

LM

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• 18.9 Diverse molluscs are variations on a common body plan– Molluscs have bilateral symmetry, a complete

digestive tract, a coelom, a circulatory system, and generally separate sexes

– General body plan of a mollusc• Muscular foot• Visceral mass containing most internal organs• Mantle• Rasping radula in many

• 18.9 Diverse molluscs are variations on a common body plan Phylum Mollusca– Molluscs have bilateral symmetry, a complete

digestive tract, a coelom, a circulatory system, and generally separate sexes

– General body plan of a mollusc• Muscular foot

• Visceral mass containing most internal organs

• Mantle

• Rasping radula in many

Gastropods (“belly foot”) are the largest group of molluscs

Snails and slugsLive in freshwater, saltwater, and terrestrial environmentsMost are protected by a single spiraled shellMany have a distinct head with eyes at tips of tentacles

– Cephalopods (“head foot”) are adapted to be fast, agile predators

• Include squids and octopuses

• Except for chambered nautilus, shell is small and internal or missing

• Mouth is at base of foot

• Use beak-like jaws and radula to rip prey

• All have large brains and sophisticated sense organs

• Giant squid is largest of all invertebrates

Still on Mollusks…

•18.10 Annelids are segmented worms– A segmented body resembling a series of fused

rings is the hallmark of phylum Annelida • Probably evolved as an adaptation facilitating

movement• Allows for flexibility, mobility, burrowing

– Annelids range from less than 1 mm to 3 m in length

– Annelids are found in damp soil, the sea, most freshwater habitats

• Most are bottom-dwelling scavengers