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Worm-like Animals Characteristics • Invertebrates. • Cephalization. – Sense organs and nerve cells located at anterior end. • Coelom. Characteristics Phylum Platyhelminthes “Flatworms” • • • • • • 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. Watch This!!! Phylum Nematoda “Roundworms” • • • • • • Unsegmented cylindrical bodies. Pseudocoelom. Complete digestive tract. No circulatory or respiratory system. Mostly parasitic. 2 mm to 2 m in length. Watch This!!! Phylum Nematoda Phylum Annelida “Segmented Worms” • • • • 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. Watch This!!! Phylum Mollusca Characteristics • • • • Soft-bodied. Coelom. Two body openings. Bilateral symmetry. Body Plan • 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 • • • 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. Watch This!!! 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. Watch This!!! And This!!! Class Cephalopoda • • • • • • • 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 Watch This!!! And This!!! 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 • • • • • Complete digestive system. Simple circulatory and nervous system. No respiratory or excretory system. No head. Endoskeleton with spiny projections. Watch This!!!