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Mollusks Chapter 27 Facts and Fun Flatworms Are soft, flattened worms that have tissues and internal organ systems. The simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization Three embryonic layers include: ectoderm, endoderm, and mesoderm Closer Look Use Fig 27-3 to help you label the flatworm WORD BANK Nerve Cords Pharynx Ganglia Digestive Cavity Eyespot Flatworms Form and function Feeding Free living flatworms feed on tiny aquatic animals or they can be scavengers and feed on recently dead animals Respiration, Circulation, and Excretion Do not need circulatory system because their body is thin and flat They rely on diffusion to transport oxygen and nutrients to their internal tissues and to remove carbon dioxide and other waste. Response Head encloses several ganglia or groups of nerve cells Eyespot – group of cells that can detect changes in the amount of light in their environment. Flatworms Movement Move two ways Cilia – helps them glide through the water and over the bottom of a stream or pond. Muscle cells – twist and turn to react to environmental stimuli. Reproduction Reproduce sexually and asexually (Sexually) Hermaphrodite – an individual that has both male and female reproductive organs. (Asexually) Fission – organism splits in two and each half grows new parts to become a new organism 3 Groups of Flatworms Turbellarians Free living Live in marine or fresh water under stones, shells, sand, or mud Flukes Parasitic Infect organs of their host Live in skin, mouth, gills, or other outside parts of the host. Tapeworms Long, flat, parasitic Adapt to life inside the intestines of their host where food is absorbed through their body walls. They have no digestive tract Roundworms Unsegmented worms that have psedocoeloms and digestive systems with two openings – a mouth and an anus. Roundworms Form and function Feeding Use grasping mouthparts and spines to catch and eat other small animals. Some eat algae, fungi, or pieces of decaying organic matter Respiration, Circulation, and Excretion Exchange gases and excrete metabolic waste through their body walls. They rely on diffusion to carry nutrients and waste through their body. Response Several ganglia or groups of nerve cells Nerves that extend from the ganglia in the head and run the length of the body. Sense organs that detect chemicals given off by prey or hosts. Roundworms Movement Muscles that extend the length of their body Aquatic – contract muscles to move like snakes Soil dwelling – push their way through soil by thrashing around. Reproduction Reproduce sexually Have separate sexes – either male or female Use internal fertilization Pain and suffering in humans 4 human disease 1. Trichinosis causing worms 2. Adult worm live and mate in the intestines of the host including humans, pigs, and other mammals. Filarial worms Found in tropical regions of Asia Threadlike worms that live in blood or lymph vessels of birds and mammals Transmitted through biting insects (mosquitoes) Pain and suffering in humans 3. Ascarid worms 4. Found in humans and other vertebrate animals Causes malnutrition in more than 1 million people Absorbs digested food from the host’s small intestine. Spreads by eating vegetables or other foods that are not washed properly. Hookworms Eggs hatch outside the body and develop in soil Enters through an unprotected foot Sucks the host’s blood causing weakness and poor growth. How are the eggs released from the body? Through its feces How do the worms get back into the host (dogs)? Dog ingest the larva/egg or by eating the transport host Eating undercooked meat containing larval cysts Elephantiasis Hookworms Worms attach to intestinal wall and suck blood, causing weakness and poor growth Annelids Worms with segmented bodies Have a true coelom that is lined with tissue derived from mesoderm. Annelids Form and function Feeding Uses a pharynx that is covered with sticky mucus Pharynx holds two or more sharp jaws Feed on decaying vegetation Respiration Aquatic – use gills to breathe Land dwelling – breathe through their moist skin Circulation Have a closed circulatory system – blood is contained within a network of blood vessels Annelids Movement Move by alternately contracting two sets of muscles Longitudinal muscles – run from the front of the worm to the rear and can contract to make the worm shorter and fatter. Circular muscles – wrap around each body segment and can contract to make the worm longer and thinner. Reproduction Reproduce sexually Fertilization takes place in the clitellum – band of thickened specialized segments, secretes a mucus ring into which eggs and sperm are released. Groups of Annelids Oligochaetes Leeches Contains earthworms and their relatives Streamlined bodies Live in soil or fresh water Earthworm castings are a mixture of sand, clay, and undigested food that an earthworm expels from its anus. Parasites that suck blood and body fluids of their host. Can be used to treat medical conditions Polychaetes Marine annelids that have paired, paddlelike appendages tipped with setae. Live in cracks and crevices in coral reefs, in sand, mud, and piles of rocks. Section27–16 27-3 Figure The Anatomy of an Earthworm 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 Mollusks Soft bodied animals that usually have an internal and external shell. Include: Snails Slugs Clams Squids Octopus Mollusks Have a larval stage called trochophore. Label: A.__________________ B.__________________ C.__________________ D. _________________ Soft bodies Mollusks Form and function Body Plan Has four parts Foot - flat structures for crawling, spade-shaped structures for burrowing and tentacles for capturing prey. Mantle – thin layer of tissue that covers most its body Shell – made of glands in the mantle that secrete calcium carbonate. Visceral Mass – beneath the mantle, consists of the internal organs. Mollusks Feeding Snails and slugs use a radula – tongue like structure to which hundreds of tiny teeth are attached. Respiration Aquatic – use gills to breathe Land dwelling – breathe using a mantle cavity that has a large surface area lined with blood vessels. Circulation Have a open and closed circulatory system Open circulatory system – blood is pumped through vessels by a simple heart. Octopi and squid have a closed circulatory system Roundworms Movement Several methods Snails – secrete mucus along the base of the foot and move over surfaces using a rippling motion of the foot. Octopi draws water into the mantle cavity and then forces the water out through a siphon – a tubelike structure through which water enters and leaves the body. Reproduction Reproduce sexually Fertilization takes place in the clitellum – band of thickened specialized segments, secretes a mucus ring into which eggs and sperm are released. Groups of Mollusks Gastropods Shell less or single shelled that move by using a muscular foot located on the ventral side. Ex:Snail Bivalves Two shells that are held together by one or two powerful muscles. Ex: Clams and oysters Cephalopods Soft-bodied; head is attached to a single foot. The foot is divided into tentacles or arms. Ex: Octopus and squids Figure 27–23 The Anatomy of a Clam Section 27-4 Stomach Coelom Shell Heart Nephridium Adductor muscle Mouth Anus Excurrent siphon Adductor muscle Incurrent siphon Gills Mantle cavity Intestine Mantle cavity Foot End of class assignment Draw a snail, a squid, and a clam. (Figure 27-21- page 702) Label the foot, mantle, shell, radula, and gills. Just Slinking or Wriggling in the Rain Section 27-3 Have you ever noticed that after a spring rain, earthworms come out of the soil and appear on driveways, in puddles, and on sidewalks? Why does this happen? 1. An earthworm breathes through its skin. If its skin dries out, it cannot breathe. Why would an earthworm be more likely to “surface” during the rain than at other times? The rain keeps the skin of the earthworm moist. At other times, the earthworm is likely to dry out and suffocate. 2. What types of weather conditions might be fatal for an earthworm? Hot and dry weather is fatal for an earthworm because its skin dries out quickly.
