Ms. Moore 2/11/13 Worms and Mollusks
What is a flatworm? • Phylum: Platyhelminthes • Flatworms are soft, flattened worms that have tissues and internal organ systems. • They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, and cephalization. • Acoelomates: without coelom (fluid-filled body cavity, lined with tissue from mesoderm
Flatworms: Form and Function • Feeding: • Carnivores or Scavengers ; can be parasitic • Digestive cavity with single opening (mouth) • Pharynx: extends outside the mouth and pumps food into digestive cavity (gut) • Food diffuses from the digestive cavity into all other body tissues
Respiration, Circulation, and Excretion: • Since their bodies are so flat and thin, many flatworms do not need a circulatory system to transport materials (use diffusion). • No gills or respiratory organs; no heart, blood vessels, or blood. • Flame cells: specialized cells that remove excess water from the body; filter and remove ammonia and urea using pores of the skin
Response: • Ganglia: groups of nerve cells that control the nervous system (no brain) • Eyespot: group of cells that can detect changes in the amount of light in their environment
Movement: • Cilia on the epidermal cells help glide through the water. • Muscles controlled by the nervous system help to twist and turn to react to environment.
Reproduction: • Hermaphrodite: both male and female reproductive organs • Sexual: two worms join in a pair and they deliver sperm to each other • Asexual: fissionorganism splits in two and each half grows new parts to become a complete organism
Groups of Flatworms • Turbellarians • Flukes • Tapeworms
Turbellarians • Free-living flatworms • Most live in marine or fresh water • Bottom dwellers: living in sand or mud • Planarians: “cross-eyed” freshwater worms
Flukes • Class: Trematoda • Parasitic flatworms that infect internal organs of their host; can also be external parasites.
Tapeworms • Class: Cestoda • Long, flat, parasitic worms that are adapted to life inside the intestines of their hosts. • Scolex: contains suckers or hooks; attaches • Proglottids: segments that make up most of worm’s body; contain male and female reproductive organs • Youngest proglottids are at the anterior end and the largest and most mature are at t he posterior. After eggs have been fertilized, proglottids break off and release zygotes that are passed out of the host in feces/ • Testes: fertilize eggs of other tapeworms or of self
What is a Roundworm? • Phylum: Nematoda • Roundworms are slender, unsegmented worms with tapering ends; Range in size from microscopic to a meter in length • Pseudocoelom: false coelom (only partially lined with mesoderm • Digestive tract with two openings—mouth and anus (posterior opening of digestive tract) • “tube within a tube”: inner tube is digestive tract and outer tube is body wall • Food moves in one direction
Roundworms: Form and Function • Feeding: • Carnivorous: eat small animals by latching on to them with grasping mouth parts and spikes • Scavengers: eat algae or decaying mater • Consume bacteria and fungi • The free living roundworms tend to be more complex than parasitic roundworms.
Respiration, Circulation, and Excretion • Diffusion through body walls • Response • Simple nervous systems with several ganglia; sense organs that detect chemicals given off by prey or host • Movement • Muscles extend length of body; function as hydrostatic skeleton • Reproduction • Sexually with male and female worms • Internal fertilization
Roundworms and Human Disease • Trichinosis-Causing Worms • Caused by Trichinella roundworm • Worms burrow into intestine walls and females release larvae that travel through the bloodstream and live in organs and tissues of host’s body
Filarial Worms • Found in tropic regions of Asia; live in blood and lymph vessels of birds and mammals (humans) • Transmitted host-to-host by biting insects like mosquitoes • Large numbers could block lymph passageselephantiasis
Ascarid Worms • The cause of malnutrition of more than 1 billion people worldwide. • Ascarislumbricoidesusually spread by eating vegetables that are not washed properly.
Hookworms • 25% of the world’s population is infected with these worms • Eggs hatch outside the body and mature in the soil • Use tooth-like plates to burrow into skin of an uncovered foot and live in bloodstream • Suck blood and cause weakness and poor growth
Research on C. elegans • DNA sequence has been mapped out (97 million bp) • Help us find out how eukaryotes become multicellular and how multicellular animals are similar and different
What is an Annelid? • Phylum: Annelida; “little ring” • Septa: internal walls between each body segment • Setae: bristles attached to each segment • Annelids are worms with segmented bodies • Have true coelom that is lined with tissue derived from mesoderm. • Like roundworms, annelids have a tube within a tube system with an anus.
Annelids: Form and Function • Feeding and Digestion • Range from filter feeders to predators • Use a pharynx that hold two or more sharp jaws used to attack prey. • Earthworms: pharynx pumps food into esophagus moves to crop (storage) through gizzard (ground into smaller pieces) intestine
Circulation • Closed Circulatory System: blood is contained within a network of blood vessels • Earthworm: blood circulates through two major blood vessels • Dorsal runs to head; ventral runs to tail • Dorsal functions as a heart due to contractions = pump blood
Respiration • Aquatic annelids breathe through gills • Land-dwelling annelids take in oxygen and give off carbon dioxide through moist skin; mucus • Excretion • Digestive waste passes through the anus • Cellular waste eliminated by nephridia (excretory organs that filter fluid in the coelom)
Response • Brain and nerve cords • Marine annelids are more developed: sensory tentacles, chemical receptors, statocyts, two or more pairs of eyes • Movement • Hydrostatic skeleton • Longitudinal muscles: front to rear; muscles contract to make worm shorter and fatter • Circular muscles: contract to make worm longer and thinner • Marine annelids: paddle like appendages (parapodia)
Reproduction • Sexually: external fertilization • Hermaphrodites: two worms exchange sperm and store them in special sacs • Clitellum: band of thickened, specialized segments, secretes a mucous ring into which sperm and egg are released; rings slips off and forms a cocoon; worms hatch weeks later
Groups of Annelids • Class: Oligochaetes • Annelids that typically have streamlined bodies and relatively few setae; soil or freshwater • Castings: mixture of sand, clay and undigested food that an earthworm expels from its anus.
Class: Hirudinea • Leeches • External parasites that suck the blood and body fluids of their host • ¼ are carnivorous that that feed on soft-bodies invertebrates • Suckers at both ends of body • Proboscia: muscular extension that can be forced into tissue of host • Can release a substance that anesthetizes wound and prevents blood from clotting.
Class: Polychaeta • Polychaetes • Marine annelids that have paired , paddle like appendages tipped with setae
Ecology of Annelids • Earthworms (and other annelids) burrow through soil, aerating it and mixing it to depths of two meters or more • Mine minerals from deeper soil layers • Diets of many birds and other vertebrates
What is a Mollusk? • Phylum: Mollusca • Mollusks are soft-bodied animals that usually have an internal or external shell. • Ex: snails, slugs, clams, squids, and octopi. • Trochophore: free-swimming larval stage • Characteristic of Annelida = related 550 m.y.a.
Form and Function: Mollusks • True coeloms and organ systems • Body Plan (4 basic parts): • Foot: muscular structure used for crawling, burrowing, and capturing prey • Mantle: thin layer of tissue that covers the body (cloak) • Shell: glands in mantle secrete calcium carbonate; reduced or lost in slugs and other mollusks • Visceral Mass: beneath mantle; consists of internal organs (Figure 27-21)
Feeding: • Can be herbivores, carnivores, filter feeders, detritivores, or parasites • Radula: flexible tongue-shaped structure used by snails and slugs; 100s of teeth are attached • Octopi use sharp jaws and tentacles to feed • Clams, oysters, and scallops filter feed with their gills and mucus • Siphon: tube like structure where water enters and leaves the body
Respiration: • Use gills inside their mantle cavity • Land species have no gills, but they do have thin blood vessels in mantle that stay moist for oxygen passage. • Circulation: open or closed • Open circulatory system: blood is pumped through blood vessels by a simple heart; the blood makes way through body to the gills, then back to the heart; found in slow moving mollusks • Closed circulatory system: used in fast-moving mollusks bc it moves blood through body faster • Excretion: • Cells release wastes into blood and nephridia remove it from the body
Response: • Slugs use simple ganglia and octopi use complex brain • Complex brain allow them to remember things and be trained for reward or avoid punishment • Movement: • Slugs secrete mucus and use their foot to glide • Octopi use jet propulsion • Reproduction: • Sexually by internal or external fertilization • Can be hermaphrodites, but do not fertilize own eggs
Groups of Mollusks • Gastropods • Class: Gastropoda • Gastropods are shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side • EX: snails, land slugs, sea butterflies, and sea horses • Protection: some can retract back into their shell or use ink to make a smoke screen; some produce chemicals that make them taste bad; nudibranchs can recycle nematocysts and use them
Bivalves • Class: Bivalvia • Bivalves have 2 shells held together by one powerful muscle • EX: clams, oysters, mussels, and scallops • Most stay in one spot for long periods of time, except scallops (move to run from predators) • Eat through filter feeding or sifting through the mud.
Cephalopods • Class: Cephalopoda • Cephalopods have a head that is attached to their foot which is divided into tentacles or arms (8+). • EX: octopus, squids, cuttlefishes, nautiluses • Nautiluses are the only ones with external shells; they have over 90 tentacles; control water depth by amount of gases in their mantle • Octopi have lost shells completely • Cuttlefishes have small shells inside their body
Ecology of Mollusks • Mollusks can be used to detect water quality • Filter algae out of the water • Live symbiotically with other organisms • Major food source for humans