WORMS AND MOLLUSKS

Ms. Moore 10/18/12

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

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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. Ascaris lumbricoides usually

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