1. Platyhelminthes

2. General Characteristics
They exhibit bilateral symmetry: anterior and posterior ends are different; so are the dorsal (top) and ventral (bottom) surfaces
The platyhelminths also exhibit some degree of cephalization. Commonly referred to as the 'flatworms' because their bodies are dorsoventrally flattened.
They are acoelomates
This phylum (and all remaining phyla) possess 3 germ layers (=triploblastic)
The mesoderm (third germ layer) gives rise to muscles, various organ systems, and the parenchyma, a form of solid tissue containing cells

3. Outer Body Covering
The body of some platyhelminthes (e.g., turbellarians) is covered by a ciliated epidermis
Epidermal cells contain rod-shaped structures called rhabdites that when released into the surrounding water, expand and form a protective mucous coat around the animal
The outer body covering of other platyhelminthes (e.g., parasitic forms) is a non-ciliated tegument
The tegument is referred to as a syncytial epithelium

6. The intestine, with only one opening, is a blind system
Organ Systems of the Platyhelminthes
Digestive System
Some of the flatworms possess a digestive system, with a mouth, pharynx, and a branching intestine from which the nutrients are absorbed
The intestine, with only one opening, is a blind system

9. Muscular System
Below the epidermis are layers of circular and longitudinal muscle fibers; used in locomotion

10. Nervous System
Includes: anterior cerebral ganglia, longitudinal nerve cords, and some lateral nerves
Most free living planarians and parasitic larval forms possess a variety of sensory organs (e.g., eye spots, statocysts, rheoreceptors)

11. Reproductive System
Most are capable of some form of asexual reproduction (e.g., many turbellarians reproduce by fission)
Most flatworms are hermaphroditic; however, they often pair with other individuals to exchange gametes

12. Platyhelminthes Taxonomy
Class Turbellaria
Free-living flatworms; mostly marine organisms
Range in size from microscopic (interstitial species between sand grains) to extremely large (two feet)
Locomotion
Most move by means of cilia and mucous
Muscle contractions also permit turning, twisting and folding of the body

13. Nutrition
Turbellarians are carnivores and prey on other animals or eat dead animal remains.
Planarians have a muscular pharynx that they can insert into their prey and then pump to bring in food fragments
These animals have a highly divided gut to greatly increase the surface area for digestion and absorption
Senses
They have well developed sensory structures, including eyespots, mechanoreceptors, and chemoreceptors

14. Reproduction
Planarians are capable of asexual reproduction via fission
Also capable of regeneration; exhibit both anterior- posterior and lateral polarity
They are hermaphrodites but usually exhibit cross-fertilization
The penis of some turbellarians is modified as a hollow stylet; sperm tranfer is by hypodermic impregnation, in which the copulating partners stab each other and inject sperm

15. KELAS TURBELARIA