25.1 Flatworms *Phylum Platyhelminthes – the least complex worms *Examples – Flukes, Tapeworms, and Planarians I. Planarians Page737 Structures – head, eyespots, sensory pits, mouth, pharynx, cilia, digestive tract, flame cells A. Feeding and Digestion – the planarians extend their pharynx out of their mouth. The pharynx releases chemicals that help break down the food before it is brought into the mouth. B. Nervous System – a ganglion (a mass of nerve cells that act as a brain) sends messages the eyespots and the sensory pits have received. C. Reproduction – Hermaphordites The fertilized eggs are released into the water where they hatch into planaria. ***These animals are unique because they can regenerate. If they are cut in half, the head will grow a new tail and the tail will grow a new head. II. Parasitic Flatworms – get their nutrients by living inside of a host A. Structures of a Tapeworm Scolex - Proglottids - 25.2 Roundworms I. Phylum Nemotoda Live in soil, fresh and salt water, and animals Parasitic and Free-living Almost all animals and plants are affected by roundworms They have a thick outer covering that protects them when they are swallowed by their host. Movement – they have a pair of length-wise muscles; as one pair relaxes, the other contracts and causes them to thrash around. Examples 1. Hookworms a. The female is 11 mm and the male is 9 mm b. c. Moves from eggs in the soil to the skin to the intestines of the host 2. Trichella a. Eating improperly cooked pork b. 3. Pinworms – most common a. 30% of childern are affected and 16% of adults b. c. Lay eggs in the anal area d. Causes scratching 4. Ascaris a. The female can lay 200,000 eggs per day b. Passed out of the host feces c. Live in the alveoli - causes serious pneumonia d. e. 25.4 Segmented Worms – Phylum Annelida Examples – bristleworms, earthworms, and leeches Annelid - “tiny rings” Approximately 9000 species I. Segments A. The body is divided into segments which are seen internally as well as externally. Each segment has its own set of muscles which help in movement B. The segments are grouped according to function. Most of the segments contain excretory organs and nerves. C. Segmented worms can found everywhere; from extreme heat to extreme cold. They cannot be found in the sand or frozen soil. II. The Earthworm A. External Structures 1. Cuticle – the outer body layer of slimy mucus 2. 3. B. Setae – the stubby bristles on the ventral side (the belly) 1. Helps hold the worm in its burrow 2. C. The anterior (the head) of the earthworm is darker and more pointed than the posterior end. D. Clitellum – the raised portion used for reproduction Internal Structures E. Circulatory System 1. Aortic arches - 2. Dorsal vessel – pumps blood to the head and the ventral vessel pumps blood to the tail. F. Digestive System 1. Esophagus – the food tube 2. Crop - 3. Gizzard - G. Excretory System 1.Nephridia - collect waste materials from the blood and fluids H. Nervous System 1. Ganglion – a mass of nerve cells that acts as a brain 2. Ventral Nerve Cord – collects messages and sends the messages to the ganglion .