Three most common worm phyla~
1. Platyhelminthes (flat worms)
2. Nematoda (round worms)
3. Annelida (segmented worms)
All worms:
*Are soft-bodied
*long
*legless (a few have appendages)
*have bilateral symmetry
*Cephalization ~ an anterior, or head region where most of the
sensory organs and nerve cells are concentrated.
*Bodies develop from 3 cell layers
a. Ectoderm - Epidermis
b. Mesoderm
c. Endoderm - Gastrodermis
Embryology
Germ Layers
Wikipedia
• Triploblasty is a condition of the blastula in which there are three primary germ
layers: the ectoderm, mesoderm, and endoderm. The germ layers form during
gastrulation of the blastula. Additionally, the term may refer to any ovum in which
the blastoderm splits into three layers.
• All higher and intermediate animals (from flat worms to humans), arise from a
triploblastic ovum. Triploblastic organisms are organisms which develop from such
an ovum. Generally speaking, triploblastic organisms belong to the Bilateria
subregnum. Triploblastic organisms generally possess bilateral symmetry, which is
where the clade Bilateria takes its name.
• Simpler animals qualified as diploblastic, such as cnidaria (which include jellyfish,
corals and hydra), possess two germ layers. Even simpler animals such as sponges
within the formally termed Porifera phylum contain no true tissues.
Germ Layers
Earthlife.net
• Diploblastic animals have two cell layers to their bodies, an outer Ectoderm and an
inner Endoderm, between these two layers may be an amount of noncellular
material. Triplobastic animals have 3 cell layers in their bodies, Ectoderm (Outer
layer) Mesoderm (middle layer) and Endoderm (inner layer), simpler animals have
only 2 cell layers in their bodies and are called diploblastic. Body cavities of any sort
only exist in triploblastic animals. These layers form in the embryo during a process
called gastrulation and later give rise to different parts of the body. Thus the
Ectoderm will eventually become, the epidermis of the skin, sweat and sebaceous
glands, epidermal coverings (hair, feathers, scales, horns etc.) and the nervous
system including those parts of the sense organs that are sensory, rather than
supportive. The mesoderm gives rise to the skeleton, the muscles, the dermis of
the skin, blood and blood vessels, mesenteries and the lining of the coelomic
cavity. From the endoderm arise the lining of the guts, lungs and urethra as well as
the urinary bladder, the thyroid, parathyroid and thymus and the secretory parts of
the liver and pancreas.
Body Cavity
Earthlife.net
•
Acoelomate animals are called acoelomates and they have no true body cavity. The
acoelomate phyla are Placozoa , Porifera , Cnidaria , Ctenophora , Platyhelminthes, Mesozoa,
Nemertina, Gnathostomulida.
Pseudocoelomate animals have a pseudocoelom. They have a body cavity but it is not lined
with mesodermal cells. It exists between the mesoderm and the endoderm that makes up
the walls of the gut. It does not have supportive mesodermal mesenteries. The
pseudocoelomate phyla are Gastrotricha, Rotifera, Nematoda, Nematomorpha, Kinorhyncha,
Loricifera, Acanthocephala.
Coelomate animals have a coelom, this is a body cavity that has a mesodermal lining.
Coeloms arise in two different ways. Through splitting of the mesoderm cell mass which
arises from the walls of the archenteron in which case it is called a schizocoelom. Or from
the invagination of parts of the endodermal aspect of the archenteron, when it is called an
enterocoelom. The coelomate phyla are Entoprocta, Ectoprocta, Phoronida, Brachiopoda ,
Mollusca, Priapulida, Sipuncula , Echiura, Annelida, Tardigrada, Pentastoma, Onychophora,
Arthropoda, Pogonophora, Echinodermata, Chaetognatha, Hemichordata, Chordata.
Body Cavity
Phylum Platyhelminthes
Have a thin, flat body, so are commonly called flatworms
1. Class Turbellaria- Free living flatworms ~
*illustrated by planarians, basically s strip of flat tissue that ends in a triangular
point.
*Have eye spots that can detect the presence and direction of light.
*Have an elaborate nervous system, having a mass of nerve tissue in the head, two
longitudinal nerves and several transverse nerves
*Has cilia on its ventral surface to propel it over the layer of slime it secretes.
*Epidermis, or outermost covering, is very thin.
*Also contains gastroderm and mesoderm.
*Has flame cells ~ hollow bulbs containing a tuft of cilia that beat vigorously, used to
aid in excretion of wastes and excess water.
*Asexual regeneration and sexual reproduction. All are hermaphrodites
Digestion
• Pharynx- muscular tubelike structure that extends
out of the mouth and sucks up food particles
• Branched intestines- enzymes partially digest food
in the intestines
• Cells lining intestine engulf and complete digestion
• Indigestible food is egested back through the
pharynx
Respiration and Circulation
• The thin body and extensive digestive tract of
the planarian keep most of the animal’s cells
near food and the environment.
• Diffusion on the cellular level can thus
accomplish respiration and circulation
efficiently.
http://www.youtube.com/watch?v=Fq_aSR5FK0Y&feature=fvwrel
http://www.youtube.com/watch?v=osuABmTutZM
2. Parasitic flatworms ~ depends on the host for nourishment
Scientists divide parasitic flatworms into two groups: flukes and tapeworms
Phylum Platyhelminthes
Class Trematoda: The Flukes
Class Cestoda: The Tapeworms
*Few sensory organs as adults
*No external cilia as adults
*Tegument ~ thick protective body covering
* Suckers and/or hooks for attachment to hosts
Tapeworm
Proglottids - segments of body of tapeworm for
reproduction.
Scolex - bulb-shaped head
http://www.denniskunkel.com/DK/Misc._
Invertebrates/23995C.html
Phylum Platyhelminthes
Class Trematoda
Sheep Liver Fluke – Fasciola hepatica
cdc.gov
Fascioliasis- People usually become infected by eating raw watercress or other water
plants contaminated with immature parasite larvae. The immature larval flukes
migrate through the intestinal wall, the abdominal cavity, and the liver tissue, into the
bile ducts, where they develop into mature adult flukes, which produce eggs. The
pathology typically is most pronounced in the bile ducts and liver.
1.
2.
3.
4.
5.
6.
7.
Adult fluke in liver of sheep or human
Adult fluke releases fertilized eggs which are egested with feces
Eggs hatch releasing ciliated larva in a body of water
Ciliated larva enter a snail= intermediate host- temporarily harbors immature parasite
Immature fluke develops and reproduces asexually in snail
Young flukes leave snails and attach to vegetation as cysts
Sheep or human eats the plant with the cyst
http://www.cdc.gov/parasites/fasciola/
Phylum Platyhelminthes
Class Cestoda
Pork Tapeworm – Taenia solium
cdc.gov
Taeniasis- in humans is a parasitic infection caused by the tapeworm species Taenia
saginata (beef tapeworm), Taenia solium (pork tapeworm), and Taenia asiatica (Asian
tapeworm). Humans can become infected with these tapeworms by eating raw or
undercooked beef (T. saginata) or pork (T. solium and T. asiatica). People with taeniasis
may not know they have a tapeworm infection because symptoms are usually mild or
nonexistent.
Cysticercosis- A parasitic tissue infection caused by larval cysts of the tapeworm Taenia
solium. These larval cysts infect brain, muscle, or other tissue, and are a major cause of
adult onset seizures in most low-income countries. A person gets cysticercosis by
swallowing eggs found in the feces of a person who has an intestinal tapeworm.
http://www.cdc.gov/parasites/taeniasis/
http://www.cdc.gov/parasites/cysticercosis/
Life Cycle Resulting in Taeniasis
1. Each proglottid produces, fertilizes, and stores eggs as it lives
inside human
2. Mature proglottid breaks off and is egested with feces
3. Pig (intermediate host) eats proglottid
4. Eggs are released and hatch in pig intestine
5. Larvae enter blood stream and are transported to muscle
tissue throughout pigs body
6. Larvae form cysts or bladdar worms on muscle tissue
7. Human eats poorly cooked pork
Branch off The Life Cycle Resulting
in Cysticercosis
1. Each proglottid produces, fertilizes, and stores eggs as it lives
inside human
2. Mature proglottid breaks off and is egested with feces
3. Human (intermediate host) eats proglottid
4. Eggs are released and hatch in human intestine
5. Larvae enter blood stream and are transported to muscle
tissue throughout the humans body
6. Larvae form cysts or bladdar worms on muscle tissue in
human