1. 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

2. LE 18-08a Mouth

3. –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

4. LE 18-08b Muscle tissueTrichinella juvenile LM 350 

5. 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

6. 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

8. Gastropods (“belly foot”) are the largest group of molluscs Snails and slugs Live in freshwater, saltwater, and terrestrial environments Most are protected by a single spiraled shell Many have a distinct head with eyes at tips of tentacles

12. –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…

15. 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