group 3 zoo

• Platyhelminthes are invertebrate organisms, also called flatworms, which have a flat and soft bodies
• The majority of Platyhelminthes are parasitic, which means they rely on other organisms for a food source. But some of them are capable of free living
• Platyhelminthes


  Flatworms that lack coelom; many are parasitic; all lack either a circulatory or respiratory system
• Platyhelminthes lineage


  • Catenulida
  • Rhabditophora
• Catenulida


  • A small clade of just over 100 species
  • They typically reproduce asexually by budding
  • They feed on small invertebrates and algae that they capture from the water column
• Catenulida includes most parasitic worms (including members of Trematoda, Monogenes, and Cestoda) as well as free-living flatworms that have been previously classified under Turbellaria

  
• General characteristics of Platyhelminthes

  • They are triploblastic, acoelomate, and bilaterally symmetrical
  • May be free-living or parasitic
  • Has a soft covering with or without cilia
  • Their body is dorsoventrally flattened without any segments and appears like a leaf
  • Devoid of the anus and circulatory system but have a mouth
  • Respire by simple diffusion through the body surface
  • Have an organ level of organization
  • Do not have a digestive tract
  • Are hermaphrodites and can regenerate
  • Have sexual reproduction: fusion of gametes; asexual reproduction: regeneration by fission
• Unique characteristics of Platyhelminthes

  • Parenchyma cells: A connective tissue that fills in between the body wall and organs, helping in transporting the food material
  • Flame cells: They have flame cells which help in excretion and osmoregulation
  • Nervous system: They have a nervous system that comprises the brain and two longitudinal nerve cords arranged in larger like fashion animals: tapeworms, flukes, and planarians
  • Can self-fertilize
• Flatworms exhibit cephalization, which means they have a distinct head and tail region
• Platyhelminthes are known as acoelomates, which means "without a coloem"
• Three embryonic layers of Platyhelminthes

  • Ectoderm: gives rise to surfaces that cover tissues
  • Mesoderm: internal tissues
  • Endoderm: lines the digestive system
• Feeding or Digestion


  They can be carnivores that feed on tiny aquatic animals or they can be scavengers. Flatworms only have one opening through which foods and waste pass
• Habitat


  Usually live under water in sandy areas, but some can live on a host (for example, a tapeworm) and others can live in soil
• Classifications of Platyhelminthes


  • Turbellaria (Planarians)
  • Trematoda and Monogenea (Flukes)
  • Cestoda (Tapeworms)
• Turbellaria (Planarians)


  • Includes mainly free-living, marine species, although some species live in freshwater or moist terrestrial environments
  • Most are less than five millimeters (0.2 inch) long, and many are microscopic
  • Hooks and suckers are not present
• Trematoda and Monogenea (Flukes)

  • Are internal parasites of mollusks and many other groups, including humans
  • Trematodes have complex life cycles that involve a primary host in which sexual reproduction occurs and one or more secondary hosts in which asexual reproduction occurs
  • The primary host is almost always a mollusk
  • They are flattened, leaf-like body with simple digestive tracts
  • Hooks and suckers are usually present

  
• Cestoda (Tapeworms)


  • Are also internal parasites, mainly of vertebrates, that live in the intestinal tract of the primary host, remaining fixed by using a sucker on the anterior end, or scolex, of the tapeworm body
  • Are exclusively parasitic and have hooks and suckers
  • They do not possess a digestive system

  
• Life cycle of Cestoda

  1. Taenia solium (pork tapeworm)

  2. Taenia saginata (beef tapeworm)

  3. Diphyllobothrium latum (fish or broad tapeworm)

  4. Hymenolepis nana and Hymenolepis diminuta (dwarf tapeworm and rat tapeworm)

  5. Echinococcus granulosus and Echinococcus multilocularis (cause hydatid disease)

  
• Liver fluke (Fasciola hepatica)


  • An endoparasite that is known to cause a disease called liver rot
  • These endoparasites are found in the bile ducts of sheep, cattle, goats, and even in a few other vertebrates
  • They can live solitarily or together in a host

  
• General characteristics of liver flukes

  • Anterior end is produced into a conical projection called the cephalic cone
  • Mouth is situated ventrally at the anterior end, and it is surrounded by oral sucker
  • Has highly muscular ventral sucker or acetabulum is situated a little posterior to the oral sucker
  • The posterior end is large and more rounded in the front than the back
  • The digestive system comprises esophagus, pharynx, and diverticulated intestine
  • Excretory pore is situated at the posterior extremity
  • They are hermaphrodites
  • Eggs are passed to the exterior through the median genital pore present between the ventral and oral suckers

  
• Life cycle of liver flukes

  1. Adult fluke lay eggs that are passed out onto pasture in the faeces

  2. At suitable temperatures, a miracidium develops within the egg, hatches, and migrates in thin films of moisture, actively seeking the snail host

  3. Miracidia can only survive for a few hours outside the snail

  4. Within the snail they undergo two further developmental stages, including multiplication, eventually becoming infective cercariae, which emerge from the snail when the temperature and moisture levels are suitable

  
• Compared to other helminths, the lifecycle of liver flukes is complex and involves an intermediate host, the mud snail Galba (Lymnaea) truncatula and several free-living stages

  
• Detailed life cycle of liver flukes

  1. The life cycle begins on the adult flukes that live on the bile duct of their host

  2. The adult flukes lay eggs that will be passed onto the host's feces

  3. After that, the egg will proceed to the "miracidium stage", which they will hatch into "miracidia" or a "free-swimming larva"

  4. They require a moist environment to hatch

  5. As they reach the miracidium stage, they will seek for a host, which is a snail, so that they can develop into sporocyst and will further develop into cercariae

  6. When they become a cercariae, this is the time that it will emerge from the snail and will swim into the water or suitable vegetation to live

  7. After they find a vegetation, they will be enclosed in cysts and will transform into "metacercariae"

  8. This is the time that they will wait when to be ingested by the host

  9. The host could be infected by this metacercariae through ingesting contaminated water or food. It can also enter the body of the host through direct skin contact with contaminated water or food

  10. Next is the infective stage, which is when they will enter the second host and will migrate to the liver through the bloodstream

  11. In the liver, they will transform into adult flukes and later on migrate to the bile duct of the host, where they will reproduce sexually, releasing eggs that will be excreted on the hostʼs feces for the next life cycle

  
• Amphibians are ectothermic (cold-blooded) vertebrates that derive body heat from the environment
• Amphibians are typically aquatic as larvae and terrestrial as adults. They are highly dependent on water and are associated with freshwater habitats – none live in the sea
• Amphibian eggs are hatched into larvae (called tadpoles in frogs and toads) that live in the water for an extended period
• Amphibian larvae undergo a complex transformation, called metamorphosis
• In frogs and toads, the tail is reabsorbed during metamorphosis and the limbs develop

  
• Amphibian skin


  • Contains glands, is commonly moist, and lacks scales, feathers, or hair
  • Most amphibians have lungs but all, to a greater or lesser extent, take in oxygen through their skin
  • The skin is also important for taking in water from the environment and contains numerous pigment cells that give it color
  • Many amphibians are brightly colored; this is especially common in poisonous species, in which striking colors and skin patterns serve as a warning
  • In other species, skin coloration provides camouflage or plays a role in mate selection
• Amphibians have diverse life histories. While many produce very large numbers of eggs that they do not care for, others have evolved parental care in which a small number of eggs are protected by one or both parents
• Parental care is usually provided by the female in caecilians, newts, and salamanders, but in many frogs, it is provided by the male
• Lacking a shell, amphibian eggs need protection against dehydration and infection by fungae, as well as from predators
• General characteristics of amphibians

  • Can live both on land and in water
  • Ectothermic animals
  • Their body is divided into head and trunk
  • Skin is smooth and rough without any scales, but with glands that make it moist
  • Have no paired fins
  • Have two pairs of limbs for locomotion
  • Three chambered hearts
  • Kidneys
• Amphibians


  • They do not regulate their body temperature internally like mammals do
  • Their body temperature changes with the environment
  • Their body is divided into head and trunk
  • They do not have necks or tails in their adult form
  • Their body structure is simpler, consisting only of a head and a trunk
• Amphibian skin


  • It is smooth and rough without any scales
  • It has glands that make it moist
  • It is permeable, allowing them to absorb water and oxygen directly from their environment
  • It secretes mucus to keep it moist and aid in absorption
• Amphibians


  • They have no paired fins
  • They have limbs for movement on land
  • They have two pairs of limbs for locomotion
• Amphibian heart


  • It is three chambered, consisting of two atria and one ventricle
  • This is different from mammals, which have a four-chambered heart
• Amphibian kidneys


  • They are mesonephric, responsible for waste excretion and osmoregulation
• Amphibians


  • They possess ten pairs of cranial nerves that provide their senses and control their facial muscles
• Apoda (Gymnophiona or Caecilia)


  The smallest of the three major groups of amphibians