Platyhelminthes-Amphibia 2

• Platyhelminthes


  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
• 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.

  
• Platyhelminthes


  • They are triploblastic, acoelomate, and bilaterally symmetrical
  • May be free-living or parasitic
  • Have 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
• 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. They have bilateral symmetry. Platyhelminthes are known as acoelomates, which means "without a coloem".
• Three Embryonic Layers

  • Ectoderm - give 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.
• Platyhelminthes Classifications

  • 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 a 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 have no distinguishing behavior traits or social systems
  • They can live solitarily or together in a host

  
• Liver Fluke (Fasciola hepatica)


  • 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 Fluke (Fasciola hepatica)


  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

  5. The cercariae encyst as metacercariae on vegetation

  6. The metacercariae are ingested by the definitive host, excyst in the intestine, migrate to the liver, and develop into adult flukes

  
• Amphibia


  Derived from the Greek word "amphibious", whereas "amphi" means "both" and "bios" means "life", simply means "living a double life"
• Amphibia


  • They are ectothermic (cold-blooded) vertebrates the derive body heat from the environment
  • They 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
  • Eggs are hatched into larvae (called tadpoles in frogs and toads) that live in the water for an extended period
  • Larvae undergo a complex transformation, called metamorphosis
  • In frogs and toads, the tail is reabsorbed during metamorphosis and the limbs develop
• Amphibian Skin


  • The 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
• Amphibian Parental Care


  • 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
• Amphibians can live both on land and in water. This is because amphibians, such as frogs and salamanders, are adapted to both environments. They are born in water where they breathe through gills, like fish. As they mature, they develop lungs and legs for living on land.
• Amphibians


  • Ectothermic animals. This means that amphibians cannot regulate their body temperature internally like mammals do. Instead, their body temperature changes with the environment
  • Their body is divided into head and trunk. Unlike mammals, amphibians do not have necks or tails in their adult form. Their body structure is simpler, consisting only of a head and a trunk
  • Skin is smooth and rough without any scales, but with glands that make it moist. The skin of amphibians is permeable, allowing them to absorb water and oxygen directly from their environment. The glands in their skin secrete mucus to keep it moist and aid in this absorption
  • Have no paired fins. Unlike fish, amphibians do not have fins. They have limbs for movement on land
  • Have two pairs of limbs for locomotion. Amphibians have four limbs (two pairs), which they use for moving around on land and swimming in water
  • Three chambered hearts. Consisting of two atria and one ventricle. This is different from mammals, which have a four-chambered heart
  • Kidneys are the main excretory organs
• 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
• Caecilians


  Wormlike animals that burrow in the soil in forested areas, although some species live in rivers and streams
• Caecilians


  • They vary in length from several centimeters to more than 1.5m (5ft)
• Caecilians


  • They have tentacles on their head that are chemosensory organs that help them detect underground prey
  • They possess venom glands
  • They secrete mucus to reduce water loss and keep their skin moist
  • They resemble eels and earthworms and possess highly ossified skulls and powerful heads, which enable them to burrow deep into the soil
  • Their biology is less known than that of other amphibians
• Urodela (Caudata)


  The tailed amphibians
• Urodela (Caudata)


  • They generally lead secretive lives and live in cool, shady places, typically active at night
  • Fertilization is usually internal, with most species laying eggs but some giving birth to larvae or small adults
  • Their body is elongated with four equally sized limbs
  • Their skin is smooth with poison glands
  • The male lacks a penis and sperm is transferred to the female in a spermatophore
  • They feed on insects and worms
  • They are found under leaf litter, in the soil, or water
  • They possess hidden gills
• Amphibians


  • They have a lateral line system during their development, used to detect movement and vibration in the surrounding water
  • Their respiration is through the lungs and skin, with gills present externally for some adults
  • Sexes are separate and fertilization is usually external
  • Their development is indirect with metamorphosis
  • They breed in water as their eggs lack shells and must remain moist
• Anura (Salientia)


  The frog and toad amphibians
• Anura (Salientia)


  • There are around 3400 species in the world