Phylum: Platyhelminthes, Phylum: Nematoda, Phylum: Annelida.
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Phylum Platyhelminthes
Platyhelminthes diversity
• 20,000 known species
• Found in every habitat;
terrestrial, marine, freshwater
• Mode of living - free living or parasitic (majority)
Phylum Platyhelminthes
= flatworms
Characteristics of Platyhelminths
1. Bilateral symmetry (Simplest bilateria)
2. Triploblastic
(Simplest animals composed of
three fundamental cell layers)
Dugesia
3. No body cavity (acoelomate)
Mesoderm filled with parenchyma cells
Organ level of organization and these organs are
embedded in the mesoderm
4. Dorso-ventrally flat ;
5. Oval shape to worm like body;
- soft bodied animals
- measures 1 mm - 30 cm in length
6. Incomplete digestive tract; opens with a mouth
and ends blindly. (No anus)
Some animals do not have
a digestive tract.
7. Hermaphrodite (monocious)
Internal fertilization
between two animals
A free swimming ciliated larval stage/s in their
life cycle (some)
Müller's larva
Miracidium larva
8. Excretory organs
Function: Excretion and osmoregulation
A net work of water collecting tubules connected
to flame cells
Protonephridia
When cilia beat; they move water into the tubules
and out the body through pores called nephridiopores
9. Nervous system –
-cephalized with cerebral ganglia (brain)Cephalization and bilateral symmetry evolved together
-net work of longitudinal and lateral nerves
10. Do not have circulatory or respiratory organs.
Gas exchange is through simple diffusion
• Divided into 3 Classes
– Turbellaria
– Trematoda (Monogenea & Digenea)
– Cestoda
Phylum Platyhelminthes
Class Turbellaria
Nearly 3000 species
- Mainly free-living few are parasitic or commensal
Bdelloura on horseshoe crab
A commensal
Most are marine,
some inhabit fresh water
and moist terrestrial habitats.
They are benthic.
(bottom feeders)
Marine species are colourful.
Terrestrial turbellarians are
dull brown colour
Class Turbellaria
Rhabdites and gland cells secrete adhesive material
(mucous)
- Body cover is a multi ciliated epidermis
- Sub-epidermal rhabdites are present
- There is a basement membrane to separate epidermis
from muscle layer
-
Latin term for Class Turbellaria - "whirlpool“
is to visual impression of their
epidermal ciliary activity
– Swimming or gliding over the substrate
by action of cilia on mucous trail
– Swimming, crawling, folding or leech-like
looping movements
by peristaltic action of muscles
Locomotion/Movement
Feeding and Digestion
– Ventral mouth
– Moveable pharynx
– Extracellular digestion
• mostly carnivorous
• They have a variety of sensory cells and glands.
• Ocelli (eyespots)
-to detect light, dark, movement
• Chemoreceptors throughout epidermis
Reproduction
Asexual reproduction
1. budding
Asexual reproduction
2. Fission and regeneration
Asexual reproduction
3. Break into pieces and form a cocoon
• Internal fertilization between two animals
• Fertilized eggs are attached to
undersurfaces of stones and plants.
• Eggs hatch into miniature adult forms;
(direct development)
• Simple life cycle
Sexual reproduction
Marine forms, (not all) produce a ciliated
larva called a Müller's larva .
It is free swimming.
Ciliary lobes (6)
As the larva matures, the
compact body enlarges;
the lobes shrink and gradually
disappear.
Anterior apical organ
(brain)
Eyespots
Turbellarians are classified among 12 Orders.
Based on
- type of pharynx
- branching pattern of the gut etc….
Order Acoela
Convoluta has symbiotic
algae living beneath their
epidermis.
A mass of green colour Convoluta on the sandy beach
Mouth opens into a mass of loosely packed cells.
Order Tricladida “Planarians”
• Digestive tract - Three Diverticula
• Scavengers or active predators
Bdelloura Planaria
Order Polycladida eg. Leptoplana
• Found in tropical coral reefs.
-often mistaken for sea slugs
• Free living; carnivorous; scavengers
highly branched gut
Importance of Turbellarians:
-Colorful marine polycladids in the aquarium trade
-Dugesia is a common laboratory animal
But the vast majority of turbellarians are of little
economic importance to humans.
Humans can threaten turbellarian populations
through pollution of aquatic habitats.
Convoluta BdellouraPolycladid Planaria
Class Trematoda -Monogenea -
• Ectoparasitic on aquatic animals;
- on the gills and skin of fish
- bladder of frog
Requires Single host
• They have an opisthapter.
• It has suckers, hooks and anchors
to attach on to the host body.
Polystoma
Gyrodactylus
Simple life cycle:
Egg Ciliated larva Adult
Class Trematoda – (Sub class Digenea)
•Endoparasitic in vertebrates
• They have two suckers
- Oral sucker around mouth
- Ventral sucker
(acetabulum)
• Digestive tract consists of a
terminal mouth, muscular pharynx and
two intestinal diverticula.
- Their body cover
- is a live tegument
- has a glycoprotein layer
- No cilia
For Protection and Absorption
•Nervous system is reduced.
•Excretory system is a bladder with an excretory
pore.
• The entire body is occupied by the reproductive
system.
• Liver fluke - Fasciola hepatica
(The sheep liver fluke)
•They require two hosts to complete the
life cycle (vertebrate and a snail)
Eg. Fasciola hepatica
Sporocyst and redia
Class Cestoda -
• Endoparasites
• Adults are found only in vertebrate intestine
4000 species
Diversity
General morphology
Highly modified for parasitic life
• Long, flat, tape-like “Tapeworms”Some species can reach lengths of up to 15 m.
• No digestive tract. No mouth
- absorption through tegument
Body cover
–Tegument with glycoprotein layer
(similar to that of trematodes)
They have no sense organs
Adult body
- scolex (head)
- neck
- strobila - repeated segments
(proglottids)
New proglottids produce by neck region (Strobilization)
Each proglottid contains only reproductive organs.
Scolex consists hooks and suckers
Yolk glandMature proglottid
Mature reproductive organs
Fertilization
• - between two animals
• - between two proglottids of the same animal
• - within the same proglottid
Eggs filled uterus
A gravid proglottid consists of uterus filled with
eggs. (male organs deteriorated)
There may be 80,000 eggs in one gravid proglottid.
Gravid proglottids detach from the body and pass
out with host faeces.
Gravid proglottid
Taenia solium- Pork Tapeworm
Taeniorhynchus saginata - Beef tapeworm
Cysticercus
Onchosphere larva
Tapeworm
Require two hosts – Definitive host - man
Intermediate host - pig/cow