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Worms and Mollusks Platyhelminthes: Flatworms Nemotoda: Roundworms Annelida: Annelids Mollusca: Mollusks Worm Body Structures Phylum Platyhelminthes: Flatworms Phylum Platyhelminthes: Flatworms 1. Unique Characteristics • Soft flattened worms 2. Body Symmetry • Bilateral symmetry with head and tail Flatworms (cont.) 3. Feeding Behavior • Most are free living carnivores or scavengers • Some are parasites – absorb nutrients from host Flatworms (cont.) 4. Reproduction • Sexual hermaphrodites (have male and female parts) • Asexual - fission (cut worm and each piece grows) Flatworms (cont.) 5. Specialization and Body Structure • One opening – eat and excrete through it • Simplest organisms to have 3 tissue layers • Acoelomates – no body cavity Anatomy of a Flatworm Eyespot Ganglia Head Nerve cords Gastrovascular cavity Flatworms use a pharynx to suck food into the gastrovascular cavity. Digested food diffuses from the cavity into other cells of the body. Eyespots in some species detect light. Mouth Excretory system Freshwater flatworms have simple ganglia and nerve cords that run the length of the body. The excretory system consists of a network of tubules connected to flame cells that remove excess water and cell wastes. Ovary Testes Pharynx Most flatworms are hermaphrodites, having male reproductive organs (testes) and female reproductive organs (ovaries) in the same organism. Flame cell Excretory tubule Groups of Flatworms 6. Examples • Planarians (Turbellaria) – • Flukes (Trematoda) – • Free living in water Parasitic, infect internal organs Tapeworms (Cestoda) – Long, flat, parasitic Flatworms can cause illness… Children with blood flukes. Tapeworms Phylum Nematoda: Roundworms Phylum Nematoda: Roundworms 1. Unique Characteristics • Slender worms with tapering ends, no segments 2. Symmetry • Bilateral Roundworms (cont.) 3. Feeding Behavior • Carnivores, parasites, or detritivores • Free-living or parasitic 4. Reproduction • Sexual - most have separate males and females Roundworms (cont.) 5. Specialization and Body Structure • Two openings – tube within tube • Psuedocoelomates – 3 tissue layers and false body cavity Parasitic roundworms 6. • • • • Examples Trichnosis (meat) Heartworm (dogs) Ascaris - live in host’s intestines; causes severe malnutrition Hookworms - suck host’s blood from the intestines & the lungs Heartworm, a filarial worm Dracunculus medinensis: Guinea Worm • Filarial nematode • Ingest larvae, worm grows and migrates to skin Wuchereria bancrofti • •Filarial roundworm •Causes Elephantiasis Human intestinal roundworm: Ascaris lumbricoides • A large and common human parasite • Up to 18 inches long • 25 percent of world's population infected • Adult worms live in small intestine & eggs passed in feces • Single female produces up to 200,000 eggs daily Hookworm • 25% of people in the world have this • Eggs hatch & develop in soil • Enter unprotected skin & travel to intestines Phylum Annelida: Annelids “Little Ring” Phylum Annelida: Annelids 1. Unique Characteristics • Segmented bodies separated by septa • Help to aerate soil • Most advanced worms 2. Symmetry • Bilateral Annelids (cont.) 3. Feeding Behavior • Filter feeders to external parasites 4. Reproduction • Sexual reproduction: hermaphrodites that do not self-fertilize or separate sexes Annelids (cont.) 5. Specialization and Body Structure • • Complex organ systems Coelomates with 2 openings (simplest animals with true coelom) Groups of Annelids 6. Examples • Earthworms - live in soil, fresh water • Leeches - suck blood and body fluids • Polychaetes - marine Oligochaetes: Earthworms • Burrow, aerate, and mix soil • Food source • Feces = fertilizer Earthworm Anatomy Anus Setae Body segments Gizzard Crop Dorsal blood vessel Clitellum Mouth Brain Ganglion Circular muscle Longitudinal muscle Nephridia Ganglia Ring vessels Reproductive organs Ventral blood vessel Leeches • Can suck up to five times their own weight in blood • Used medicinally • Secrete a fluid to prevent blood from clotting Polychaetes Comparing Flatworms, Roundworms, and Annelids CHARACTERISTIC FLATWORMS ROUNDWORMS ANNELIDS Shape Flattened Cylindrical with tapering ends Cylindrical with tapering ends Segmentation No No Yes Body cavity Acoelomate Pseudocoelomate Coelomate Digestion and excretion Gastrovascular cavity with one opening only; flame cells remove metabolic wastes Tube-within-a-tube digestive tract; opening at each end; metabolic wastes excreted through body wall Tube-within-a-tube digestive tract; opening at each end; nephridia remove metabolic wastes Respiration Through skin; no respiratory organs Through skin; no respiratory organs Through skin; aquatic annelids breathe through gills Comparing Flatworms, Roundworms, and Annelids Comparing Flatworms, Roundworms, and Annelids CHARACTERISTIC FLATWORMS ROUNDWORMS ANNELIDS Circulation No heart, blood vessels, or blood No heart, blood vessels, or blood Blood circulated through blood vessels in closed circulatory system Response Simple brain; nerve cords run length of body; eyespot and other specialized cells that detect stimuli Several ganglia in head region; nerve cords run length of body; several types of sense organs Well-developed nervous system with brain and several nerve cords; many sense organs Movement Gliding, twisting, and turning Thrashing Forward peristaltic movement Reproduction Sexual (hermaphrodites); asexual (fission) Sexual (primary males and females) Sexual (some are hermaphrodites; some have separate sexes) Phylum Mollusca: Molluscs Molluscus = ‘soft’ Q:Why are clams, squids, snails, slugs, and octopi in the same family?? A:They share similar developmental stages!! Phylum Mollusca: Molluscs 1. Unique Characteristics • Soft-bodied animals with internal or external shell secreted by a mantle • Live in aquatic environments Molluscs (cont.) • Body plan – Muscular foot (to move) – Shell (not present in some) – Radula (in snails and slugs) to eat Mollusk Body Plan Squid Snail Shell Mantle cavity Foot Clam Early mollusk Gills Digestive tract Shell Formation Molluscs (cont.) Symmetry – Bilateral Feeding Behavior Some filter feed (clams, oysters, mussels) Some feed using a radula, a rough edged tongue used to scrape up food (snails, slugs) 4. Reproduction • Sexual - external fertilization 5. Specialization and Body Structure • Coelomate 2. 3. • • Groups of Molluscs 6. Examples • Gastropods (snails, slugs) – Use foot to move; 1 shell or no shell • Bivalves (clams, oysters) – Two shells held together by muscles • Cephalopods (octopi, squid) – Soft-bodies with head attached to one foot – Foot divided into tentacles or arms