ACOELOMATE ANIMALSanimals __________________ a coelom

            Phylum Platyhelminthes – flat worms

            Phylum Nemertea – ribbon worms

            Phylum Gnathostomulida – jaw worms

 

I. General Features of Acoelomate animals

 

A. _______________________________

1. Concentrating the sense organs on the head is an advantage to

active animals that seek food; this provides an anterior and

posterior end and bilateral symmetry.

 

B. Position and Biological Contributions

1. These are the simplest animals with primary bilateral symmetry.

2. They have a solid body without a coelom; they are the

_______________________________.

3. Specialization of organs provides the organ-system level of

organization.

4. Along with cephalization, this is the beginning of a

_______________________________of nervous system.

5. The simplest excretory or osmoregulatory systems appear.

6. _______________________________ have the simplest

circulatory system and a one-way alimentary canal with both mouth

and anus.

 

II. Phylum Platyhelminthes – the flatworms

 

A. Classification of Phylum Platyhelminthes

Class Turbellaria

Class Trematoda

Class Cestoidea

Class Monogenea

 

B. Characteristics

1. Flatworms vary from a millimeter to many meters in length.

2. _______________________________ are mostly free-living in

aquatic or moist terrestrial environments; some are symbiotic or

parasitic.

3. All _______________________________ and

_______________________________ are parasitic.

4. Parasitic flatworms may have several hosts in their life cycle;

some larvae may be free-living.

 

C. Form and Function

1. Tegument and Muscles

a. Most turbellarians have dual-gland adhesive organs.

1) Viscid gland cells fasten microvilli of anchor cells

to the substrate.

2) Secretions of releasing gland cells provide a

quick chemical detachment.

2. Nutrition and Digestion

a. _______________________________ have no digestive

system; they rely on the host’s digestive tract and absorb

digested molecules.

b.  The other flatworms have a mouth, pharynx and an

intestine.  Undigested food is egested back out the

_______________________________. 

(They have no _______________________________.)

c. Planaria Feeding

1) They are carnivorous and detect food by

_______________________________.

2) They entangle food in mucous secretions from

glands and rhabdites.

3) They wrap themselves around prey and extend the

proboscis to suck up bits of food.

d. Monogeneans and trematodes feed on host cells, cellular

debris and body fluids.

3. Excretion and Osmoregulation

a. Most flatworms have

_______________________________ with flame cells.

                        b. Collecting ducts join and rejoin until they empty at

                        nephridiopores.

c. Metabolic wastes are removed largely by diffusion through

the body wall.

4. Nervous System

a. One to five pairs of longitudinal nerve cords lie under the

muscle layer.

b. In most flatworms, the nerves are differentiated into

sensory, motor and association-types.

5. Sense Organs

a. _______________________________ are light-sensitive

eyespots in turbellarians, monogeneans and larval

trematodes.

b. Tactile and chemoreceptive cells are abundant, especially

in the ear-shaped auricles.

c. Some have _______________________________ for

equilibrium and _______________________________ for

sensing direction of water currents.

6. Reproduction and Regeneration

a. Fission

1) Many turbellarians constrict behind the pharynx

and separate into two animals.  Each half regenerates

the missing parts; this provides for rapid population

growth.

b. Some asexual reproduction occurs in intermediate hosts;

see life cycles to follow.

c. Nearly all are _______________________________ but

_______________________________.

d. After copulation, eggs and yolk cells are enclosed in a

small cocoon and attached by a stalk to plants.

e. Embryos emerge and resemble little adults; however,

some marine forms are ciliated and free-swimming larvae.

 

D. Class Turbellaria (e.g. ___________________)

1. Planaria, which are very small, swim by

cilia.

2. Others move by cilia and gliding over a

slime track secreted by marginal adhesive

glands.

3. Rhythmical muscular waves pass

backward from the head.

4. _______________________________

 

 

 

E. Class Monogenea

1. Monogeneans are external parasites of ___________________,

especially gills, but a few are found in bladders of frogs and turtles.

2. Monogeneans have a _______________________________ life

cycle in a _______________________________ host.

 

            F.  Class Trematoda (the _______________________________)

1. Most adults are _______________________________ of

_______________________________.

            2. Adaptations for parasitism include:

a. penetration glands,

b. glands to produce cyst material,

c. hooks and suckers for adhesion, and

d. increased reproductive capacity.

3. Sense organs are poorly developed.

4. Subclass Digenea – includes the serious fluke parasites of

humans and domestic animals.

a. Nearly all have an indirect life cycle with the first

_______________________________ host being a

_______________________________.

b. The _______________________________ or final host

is a vertebrate.  This is where _______________________

_______________________________occurs.

c. A second or third intermediate host may be required in the

life cycle.

d. They parasitize a wide range of hosts and most parts of

most systems in hosts.

e. General Digenean Life Cycle

1) The egg passes from the definitive host in excreta

and must reach water.

2) The egg then hatches into a free-swimming ciliated

larva, the miracidium.

3) The miracidium penetrates the tissues of a snail and transforms into a sporocyst.

4) The sporocyst reproduces asexually into more

sporocysts or many rediae.

5) Rediae reproduce asexually into more rediae or

into cercariae with tails.

6) Cercariae emerge from the snail and penetrate a second intermediate host or encyst on objects to become metacercariae, or juvenile flukes.

7) The adult grows from a metacercaria when it is eaten by the definitive host.

                        6.  Sheep Liver Fluke - _______________________________

was the first digenean whose life cycle was described.

 

Watch this video of a cow liver fluke turning ants into “zombies!”

This is caused by the trematode Dicrocoelium dendriticum, known as the lanceolate fluke.

 

 

7. Liver Fluke in Humans - _______________________________

a. This is the most important human liver fluke; it is common

in China, Japan and Southeast Asia.

b. It also infects cats, dogs and pigs.

c. Clonorchis Life Cycle (courtesy CDC below).

d.  Control is achieved by:  __________________________

___________________________________________

__________________________________________.

 

http://www.fao.org/docrep/008/y5970e/y5970e04.jpg

 

8. Blood Flukes - _______________________________

a. Over 200 million people have ______________________,

infection with blood flukes, commonly in Africa, South

America, West Indies, and the Middle and Far East.

b. It is unusual insofar as sexes are separate (they are

______________________).

1) The male is larger with a gynecophoric canal to

embrace a smaller female.

c.  Schistosoma Life Cycle (courtesy CDC) below.

d.  _____________________________________________

 (swimmer’s itch) occurs when cercariae penetrate an

unsuitable host such as a human.

http://www.stanford.edu/class/humbio103/ParaSites2004/Schisto/Schistomes_LifeCycle.gif

 

9. Lung Flukes – _______________________________

_______________________________ is a lung fluke that

parasitizes humans, pigs, rodents, etc.

a. Its eggs are coughed up in ________________________,

then swallowed and eliminated in feces.

b. Metacercariae develop in _________________________;

human infection occurs by eating uncooked crabmeat.

c.  Control is by ___________________________________

_______________________________________________.

10. _________________________________________________,

another trematode, lives in human intestines in India and China; it

is contracted from eating raw aquatic vegetation.

 

G. Class Cestoidea (the _______________________________)

1.  General tapeworm characteristics

            a.  A unique flattened and segmented shape compared to

            other flatworms.

b.  Each trailing segment is a

_______________________________ containing a set of

_______________________________ organs.

            1)  Proglottid formation is not “true” segmentation;

            replication of sex organs is not equivalent to

            metamerism in annelids, etc.

c.  The tegument is syncytial and has no cilia.

d. The entire surface of cestodes is covered with projections

(they look like microvilli seen in vertebrate small intestines);

these _______________________________ increase the

surface area for food absorption.

e. Nearly all are _______________________________.

f. They lack sensory organs except for modified cilia.

g. The _______________________________ is a holdfast

head portion with suckers and hooks.

h. Nearly all cestodes require two hosts; the adult is parasitic

in the digestive tract of the __________________________.

 

http://turbo.indyposted.com/wp-content/uploads/2010/12/Tapeworm.jpg

2. Characteristics of Subclass Eucestoidea – tapeworms that affect humans.

·         The chain of proglottids is called a strobila.

·         Proglottids originate in the germinative zone just behind the scolex.

·         A proglottid is usually fertilized by another proglottid in the same or different strobila.

·         Shelled embryos form in the uterus; they are either expelled or the whole proglottid is shed.

·         Over 1000 species of tapeworms are known, infecting almost all vertebrates.  Most tapeworms do little harm to the host.

 

3. Beef Tapeworm ____________________________________

a. This tapeworm lives as an adult in the alimentary canal of

humans; the juvenile form is found in

_______________________________ tissue of

_______________________________.

b. Mature adults can reach over

_______________________________ in length with

over _______________________________ proglottids.

c. The scolex has four suckers but no hooks.

d. _______________________________ proglottids (with

shelled, infective larvae) pass in _____________________.

e. Each mature proglottid has muscles and parenchyma plus

male and female organs.

f. Gravid proglottids usually crawl out of feces.

g. Proglottids rupture as they dry; embryos are viable for

_______________________________ and are picked up by

grazing.

h. Life Cycle

http://www.cals.ncsu.edu/course/zo150/mozley/fall/TapewormLC.jpg

 

i. Infection can be avoided by ________________________

________________________________________________.

 

Neural cysticercosis

http://www.cdc.gov/ncidod/eid/vol3no3/evans.gif

4. Pork Tapeworm _________________

a. This tapeworm lives as an adult in the _____________________ of

humans; juveniles live in muscles of ____________________________.

b. If eggs or proglottids are

ingested, the embryos migrate to

organs and form _____________.

c. _________________________

commonly occurs in ___________

or the _______________ causing

expected symptoms or death.

d. Infection can be avoided by

___________________________.

 

 

5. . Fish Tapeworm  - Diphyllobothrium latum

a. Adults are found in intestines of humans, dogs, cats and

other mammals; immature stages are in crustaceans and

fish.

b. It is the largest cestode of humans, reaching up to 20

meters long.

c. Fish tapeworms may occur when people eat raw fish.

6. Unilocular Hydatid - Echinococcus granulosus

a. Adults parasitize dogs and other canines; juveniles infest

many mammals.

b. Humans may serve as an intermediate host.

c. A juvenile is a special cysticercus, a hydatid cyst, that

grows for up to 20 years to a huge size.

d. Surgical removal is the only treatment.

e.  Infection occurs when people play with dogs or work in

soil where dogs have defecated and then fail to wash their

hands.

 

III. Phylum Nemertea - ribbon worms

http://upload.wikimedia.org/wikipedia/commons/thumb/4/49/Nemertea_Basiodiscus_mexicanus.png/250px-Nemertea_Basiodiscus_mexicanus.png

Nemerteans are dorsoventrally flattened.

They are the simplest animals with a blood-vascular system.

·         The blood-vascular system has a single dorsal vessel and two lateral vessels.

·         Blood is colorless and contains nucleated corpuscles.

·         There is no heart; blood is moved by muscular walls of blood vessels and by body movements.

·         Respiration occurs through the body surface.

Most are marine.

Most nemerteans are carnivorous and eat dead or living prey.

 

IV. Phylum Gnathostomulida – jaw worms

http://www.proprofs.com/flashcards/upload/a4588891.jpg

·         Over 80 species of jaw worms in 18 genera have been described.

·         They are delicate worm-like animals, 0.5 to 1 mm long.

·         They live in crevices of sediment and silt and endure low oxygen; they are often very common.

 

V.  Phylum Gastrotricha

http://www.eeob.iastate.edu/faculty/DrewesC/htdocs/gastrotrich-5.JPG

·         Gastrotrichs are similar to rotifers but are ventrally flattened, lack a corona and mastax, and are bristly or scaly.

o   They live in the interstitial spaces between benthic (the bottom of seas or lakes) particles of sand or mud.

·         Gastrotrichs are hermaphroditic.

o   Some eggs are thin-walled and rapidly develop, and some are thick-shelled for long dormancy.

o   Development is direct; juveniles have the same form as adults.