Worm Unit

Learning Target Objectives (I can…):• Distinguish between acoelomates, pseudocoelomates, and true coelomates.• Identify worm structures (anatomy) and their functions (physiology).• Classify worms based on their characteristics and associate common names (Ex: flatworms) with their scientific groups (Ex: Platyhelminthes)• Describe diseases/illnesses caused by worms, the symptoms, and how they are transmitted.• Compare/contrast types of symmetry, complete vs. incomplete digestive systems, life cycles of worms, etc.

Vocabulary:

Coelom * acoelomate, pseudocoelom, coelomate * flatworms * incomplete & complete digestive systems * flame cells * ganglia * flukes * cuticle * genital pore * Schistosoma * Bilharzia * swimmer’s itch * Fasciola hepatica * tapeworms * tegument * scolex * proglottids * roundworm * cuticle * hookworm * creeping eruption * trichinosis * elephantiasis * pinworm * annelid * metamerism * open & closed circulatory system * setae * ventral * dorsal * aortic arches * nephridia * ganglia * cerebral ganglion * ventral nerve cord * hermaphroditic * clitellum * crop * gizzard * leeches * parasites

Worms

Kingdom: Animalia

Subkingdom: Invertebrata

4 body types found in animals:

(coelom – a body cavity where organs are suspended)

(acoelomate – has no body cavity)

1) Acoelomate with 2 germ layers (ectoderm & endoderm)

- Simplest body type

- Exs: sponges and cnidarians

2) Acoelomate with 3 germ layers (ecto-, endo-, and mesoderm) Ex: flatworms

3) Pseudocoelom – (false body cavity and 3 germ layers)

The body cavity forms BETWEEN the mesoderm & endoderm. (Exs: roundworms & rotifers)

4) Coelomate with 3 germ layers. Coelom develops within the mesoderm.

(Exs: annelids, mollusks, arthropods, echinoderms, people)

- most complex body type

Phylum Platyhelminthes – flatworms

- bilaterally symmetrical

- cephalization (nerves and sensory organs concentrated at anterior end)

- definite “head” and “tail” regions

- lack (don’t have) respiratory & circulatory systems (oxygen and CO2 diffuse directly in & out of its cells)

- have all 3 (ecto-, endo-, mesoderm) tissue layers

- have true organs & organ systems (from mesoderm layer)

- No body cavity (acoloemate)

- flattened body

3 Classes of Flatworms (Platyhelminthes):

1) Class Turbellaria - most are marine (saltwater) - free-living (NOT parasitic) - one opening digestive system (food enters and wastes leave through the same opening). Food enters mouth using its pharynx (muscular tube) to pull food in. Then food goes down pharynx to intestines. Wastes follow the reverse path out. This is called an incomplete digestive system. - Flame cells – part of an excretory system for liquid wastes. These cells are lined with cilia that move liquid wastes into tubes & out through pores in the ectoderm. - movement by cilia during swimming or by sliding along on a mucus layer - simple brain formed by 2 anterior clusters of nerve cells called ganglia.

- 2 anterior eyespots (photosensitive)

- information is stored chemically & can be transferred by eating another planarian with this knowledge

- can learn

- hermaphroditic but not self-fertile (2 planarians fertilize each other at same time)

- can divide in 2 (asexual reproduction)

- can regenerate

- Most common example is the planarian.

2) Class Trematoda – (the flukes)

- parasites

- produce a non-living, protective layer called a cuticle (prevents being digested)

- usually have 2 sucker mouths (1 at head end for eating, and 1 mid-belly for clinging)

- hermaphroditic (most), with genital pore for egg release (eggs are stored in ovaries until release)

- usually classified as liver (although they can be on other organs) or blood flukes

- digestive system is NOT well developed since food is already digested for them

- most have 2 hosts

(1 vertebrate, 1 invertebrate)

Blood Flukes:

Schistosoma sp. – cause schistosomiasis

- affects 200 – 300 million people in Asia, Africa, S. America

- also known as Bilharzia (instead of schistosomiasis)

- adult worms live in human veins, spined eggs are deposited along vein walls, cut through the walls, and either make it to the bladder or the intestines to be expelled or get stuck in organs such as the liver

- snails are the second host, they are infected by the eggs which develop into small larva in freshwater

(snails are invertebrates)

- the larva penetrate human skin

(usually in less than a minute) when

people enter the water

- the thousands of spined eggs that lodge in organs are what do the most damage (300 to 3000 laid per day by ONE female)

- symptoms: bloody urine, huge abdomen (from liver and spleen enlargement). Dwarfism, death

- irrigated rice fields are common sources of infection

Schistosoma dermatitis – swimmer’s itch

- Widespread in U.S.

- a bird disease BUT the larval cercaria that emerge from the snail host can penetrate human skin part way causing intense itching for a few days. These do not get into the bloodstream to multiply.

Liver Flukes: (there are many types)

Fasciola hepatica (“hepatica” means liver)

- usually considered a sheep disease

- snail is second host

- people can get it by eating contaminated watercress

- can destroy human gallbladder & liver

3) Class Cestoda – tapeworms

- parasites

- no mouth or digestive system, they absorb nutrients right through the “skin”, the tegument

- scolex – knobby tapeworm head with

suckers and hooks to hang on with

- proglottids – behind the scolex, body

sections with nerves & flame cells & both

ovaries and testes. The worm’s length increases by growing more proglottids.

- “mature” proglottids filled with fertile

eggs break off and exit with feces of host

- humans are infected by eating under-

cooked beef (Taenia saginatta) or pork

(Taenia solium) containing tapeworm cysts.

Roundworms & Rotifers

- round body tapered on both ends

- have a pseudocoelom (body cavity between the endoderm and mesoderm) This is full of fluid. It contains the body’s organs & aids in support.

- no circulatory or respiratory system

- complete digestive system – this means food enters through 1 opening, the mouth, and wastes leave through a second opening, the anus.

Phylum Nematoda: (roundworms)

- anterior mouth & posterior anus

- some are free-living, some parasites

- at least 50 species infect man

- cuticle (outer skin that protects worm from being digested)

- separate sexes, internal fertilization (occurs within the body)

Phylum Nematoda (continued)

Ascaris lumbricoides (& the milk myth)

- eggs in contaminated food, water, or soil are swallowed. They hatch in the intestine. The larva then bore into the bloodstream, are carried to the lungs (can sometimes cause pneumonia-like symptoms), coughed up and then swallowed.

Adults develop in intestines at this point & begin producing up to 200,000 eggs per day! Adults can completely block intestines, causing death.

- eggs can lay dormant for 10 years and still hatch if they come in contact with a host

- males are smaller than females and have a hook at their posterior end

Phylum Nematoda (roundworms) continued:

Necator americanus & Ancylostoma duodenale (Hookworms)

- cutting plates at mouth “hook” into person’s intestines. They feed on blood, causing anemia (low blood count).

- common in tropical areas

- larva in soil bore through bare skin, get into bloodstream, go to lungs, get coughed up & swallowed, become adults in small intestine, produce eggs that pass in feces.

Creeping eruption – infection under the skin caused by dog or cat hookworms. The larva move into layers just below the skin but never make it into the bloodstream.

Phylim Nematoda (roundworms) continued

Trichinella spiralis (Trichinosis):

- infection occurs after eating undercooked, contaminated pork. These cysts become larva in our intestines, then adults, then new larva are produced that travel through the blood to our muscles (make cysts there), causing pain & stiffness (can even infect heart muscle).

Phylim Nematoda (roundworms) continued

Filarids:

- spread by bite of mosquito

- worms invade lymph system. Can cause swelling in tissues. Area where worms lodge usually enlarges.

- one form migrates to human eyes (Loa loa)

- one type causes elephantiasis (an enormous swelling especially of genitals)

- one type causes “heartworm” in dogs

Phylim Nematoda (roundworms) continued

Enterobius vermicularis (pinworm)

- only infects people

- common in U.S. (42 million infected)

- cause anal itching when female comes out to lay her eggs

- ingestion (or inhalation) of eggs causes

infection

Rotifers:

- often confused with protozoans such as Vorticella (which has an incomplete digestive system)

- have cilia near mouth

- complete digestive system

(not truly a “worm”)

Phylum Annelida: (annelids)

- body has several sections (segments = metamerism)

- found in saltwater, freshwater, and soil

- bilaterally symmetrical

- closed circulatory system – blood is confined to vessels

- complete digestive system

- setae = bristles found on most (not found on leeches)

- “tube within a tube”, true coelom (within mesoderm)

Phylum Annelida (continued)Class Oligochaeta (earthworms):

- circular and longitudinal muscles along interior body wall- known to carry swine flu (2nd host)- eat soil/organic matter

-Digestive system includes:muscular pharynx (sucks soil in)esophagus (tube-like)crop (temporary storage)gizzard (grinds food up)intestines (absorbs food)anus (expels wastes)

- Circulatory system includes:

1) ventral (moves blood from anterior to posterior end) & dorsal (on top side - moves blood from posterior to anterior end) blood vessels Ventral = bottom/belly side dorsal = top/”back” side 2) 5 pairs of aortic arches – link ventral and dorsal blood vessels at anterior end (sometimes called 5 hearts)

Annelids:

Respiration occurs as gas exchange across the skin. This requires moist skin. Earthworms excrete mucus to help keep their cuticle moist.

Excretion (eliminates liquid wastes & nitrogen) involves nephridia – tubes found in all segments except 4. Carry liquid wastes out.

Nervous System:

- light receptors at head and tail

- ganglia – nerve bundles in each segment that coordinate movements

- cerebral ganglion (simple brain) – coordinates body actions

- ventral nerve cord – connects peripheral nerves with cerebral ganglion

Reproduction:- hermaphroditic (both male & female parts) but not self-fertile- 2 worms line-up head to tail, exchange sperm, later form & shed egg capsule- clitellum – a swelling behind the sex organs (makes egg case)- male sex organs are found in 10th and 11th segments- female sex organs are found in 13th body segment ----- ----- ----- ----- ----- ----- ----- ----- Class Hirudinea (leeches)- most are blood eating parasites- have 2 suckers, 3 teeth (plates with ridges)- produce anti-coagulant, used in medical field- No setae