TREMATODES

• Trematodes

  • Dorso ventrally flattened, leaf like and unsegmented. Three body regions: Anterior, middle and posterior. Incomplete digestive tract and circulatory system is absent.
  • Adult are equipped with oral, ventral sucker and genital sucker;Types: monostome , amphistome , distome. All are hermaphroditic
• monostome - having a single mouth or mouthlike structure; specifically (of a digenean trematode) lacking a ventral sucker and having only an oral sucker.
• Amphistome - commonly referred to as 'stomach' or 'rumen' flukes because of the localization of these flukes in the stomach of ruminants, are digenetic trematodes distinguished by the absence of an oral sucker and the position of the ventral sucker or acetabulum at the posterior end of the body.
• Distome - A type of digenetic trematode characterized by the presence of both anterior and posterior suckers on its body surface. The anterior sucker is used for attachment to the host intestine while the posterior sucker serves as a means of locomotion within the gut lumen.
• oral sucker - located at the anterior end (near the mouth) of the organism. Its primary function is to help the organism attach to and hold onto surfaces.
• Ventral sucker - the sucker that is on the underside of the leaf. Same function as oral sucker,
• All have operculated eggs and the infective stage for all is encysted

  larva (metacercaria) except for schistosomes (cercaria).
• First IH is always a mollusc (snail), the

  second IH varies (fish, crustacean, another snail or water plants).
• Miracidium - free living, ciliated larva seeks the intermediate host.
• Sporocyst - loses larval characteristics, grows in the blood of molluscs and produces germ balls.
• Redia - sporocyst develops into active, feeding larval stage with the germ balls.
• Cercaria - larvae of leeches that are free-living and feed on blood. Free swimming larva that leaves the mollusc and enter the definitive host where it develops into an adult.
• Metacercaria - encysted (waiting) stage in second intermediate host until it is eaten by the definitive host, where it develops into an adult.
• Habitat

  Mesenteric vein - Schistosoma sp.

  Lung parenchyma - Paragonimus sp.
• Habitat

  Liver and bile - Fasciola, Clonorchis, and Ophistochis.

  Intestine - Fasciolopsis, Echinostoma, Heterophids.
• Tegument (Synctial) - is a living, complex tissue, outer covering

  Distal cytoplasm - sunken epidermis, distal, anucleate layer connected to cell bodies by internuncial processes
• Tegument

  Difference with Cestodes

  1. Spines consisting of crystalline actin
  2. Ridges, pits, and sensory papillae
  3. Vesicular inclusions
• Golgi derived vesicles, deep pit, cytoplasmic projections of gland cells
• Muscular System - circular muscles with longitudinal and diagonal

  layers
• Nervous System

  • Orthogon - with longitudinal nerve cords connected at intervals by transverse ring commissures (connecting bands of nerve tissue)
  • Cerebral ganglion nerves - (sensory endings of the oral sucker)
  • Bulbous nerve - ending with a short, modified cilium projection
  • Tangoreceptors - is sensitive to touch
  • Dorsal, lateral, and ventral (motor and sensory endings to muscles and tegument) nerve cord
• Cerebral ganglion - is a collection of neurons that connects the brain to the spinal cord.
• Eyespots - consist of one or two cup shaped pigment cells surrounding parallel rhabdomeric microvilli of one or more retinular cells
• Important Excitatory Neurotransmitter

  1. 5-hydroxytryptamine
  2. Acetylcholine

  Neuropeptides - serve as messenger systems that regulate and control a variety of bodily processes
• Excretion - Flame bulb

  Protonephridia - is a unit of an excretory system closed at the

  proximal end and opening to the exterior at the distal end by

  way of a pore.

  • Flask shaped and contains a tuft of fused flagella to provide a motive force for fluid in the system
• Feeding and digestion in trematodes vary with nutrient type and

  habitat within their host

  1. Lung flukes blood from the capillaries

  2. Intestine, urinary bladder, rectum, and bile ducts less blood and more mucus and tissue
• Pharynx - is a muscular tube like structure near the oral sucker that

  plays a vital role in the feeding process. It is surrounded by muscles that allow it to expand and contract, facilitating the ingestion of food particles
• Esophagus - is a tubular structure that connects the pharynx to the rest of the digestive system It serves as a conduit for the passage of food from the pharynx to the gut
• Ceca - Digestion in most species is predominately extracellular in the

  Gastrodermal cells - secrete digestive enzymes Proteases, dipeptidases, an aminopeptidase, lipases, acid phosphatase, and esterases
• TRUE

  • Most trematodes are hermaphroditic and some are capable of self fertilization however, require cross fertilization to produce viable progeny
  • Worms find each other by means of chemoattractants cholesterol
• Male Reproductive System

  • Usually include two testes round to highly branched
  • Vas efferens that connects with others to form a vas deferens toward the genital pore
  • Internal seminal vesicle is a muscular cirrus pouch for sperm storage
  • Ejaculatory duct is usually surrounded by numerous unicellular prostate gland cells
  • Cirrus is the male copulatory organ
• Female Reproductive System

  • Ovary is single, usually round or oval, but it may be lobated or even branched
  • Ovicapt or proximal sphincter is a short ciliated oviduct that controls the passage of ova
  • Seminal receptacle forms as an outpocketing of the wall of the oviduct
  • Laurer’s canal (vestigial vagina) is a slender tube which

  opens through the tegument
• Female Reproductive System

  • Vitelline cells are produced in follicular vitelline glands contributing to yolk in the female gamete ectolecithal system
  • Ootype is a expanded oviduct
  • Numerous unicellular Mehlis’ glands surround the ootype and deposit their products into it by means of tiny ducts
  • Egg forming apparatus, or oogenotop is a structural complex including upper uterus
  • Uterus is the expanded female duct extending to the female genital pore
  • Metraterm is the distal end of the uterus is often quite muscular functions as ovijector and as a vagina
• Female Reproductive System

  Mehlis’ gland secretions

  1. Mucoid dense bodies may serve as an adhesive mediating coalescence of vitelline globules to form the shell, or they may serve as a lubricant for the various components in the ootype
  2. Membranous bodies aggregate to surround the oocyte, two or three vitelline cells, and some spermatozoa
• 1. Aspidogastrea (aspidogaster , multicotyle) elongated flattened
  2. Digenia (Schistosoma, Fasciola, Clonochis) varied body shapes

  Oral sucker:

  1. Absent

  2. Present

  
  

  Ventral sucker/acetabulum:

  1. Multiple suckers

  2. Single ventral s.

  
  

  Complex life cycle

  1. Direct life cycle

  2. Indirect life cycle with multiple host
• At least two hosts serve in the life cycle of a typical digenetic fluke.

  1. Vertebrate in which sexual reproduction occurs
  2. Mollusc in which one or more generations are produced by an unusual type of asexual reproduction.
• Egg (Shelled Embryo)

  • Egg of trematodes is a developing (or developed) embryo enclosed by its shell, or capsule with an operculum except for blood flukes.
  • In many species an egg contains a fully developed miracidium by the time it leaves the parent, miracidia hatch while still in their parent’s uterus, and embryonate in the external environment.
• Egg (Shelled Embryo)

  F actors influencing the rate of development:

  1.Water

  2.High oxygen tension

  3.pH (4.2 to 9.0)

  4.Temperature

  5.Light

  F actors influencing hatching rate:

  1.Light

  2.Osmotic pressure

  3.Carbon dioxide tension

  4.Host enzymes
• Vitelline membrane - is the outer layer of the egg cell and is made of chorionic gonadotropin
• • Miracidium - is a tiny and ciliated organism.

  Piriform with a retractable apical papilla.

  • Apical papilla - has no cilia but bears five pairs of duct openings from glands (penetration and apical gland histolytic enzymes) and two pairs of sensory nerve endings (nerve cell bodies).
  • Sensory organs for photoreception, chemoreception, tangoreception , and statoreception adaptations.
  • Free swimming miracidia are very active since they can survive for only a few hours.
  • Mucus produced by the snail is a powerful attractant for miracidia.
• • Sporocyst (Germinal sac)

  Miracidia undergo metamorphosis near their site of penetration

  (foot, antenna, gill)

  Extensive changes:

  1. Loss of ciliated epithelial cells
  2. Formation of new tegument with its microvilli.
  3. All other miracidial structures generally disappear except for subtegumental muscle layer and protonephridia

  • Embryos in a sporocyst may develop into another sporocyst generation (daughter sporocysts), into a different form of germinal sac ( redia ), or directly into cercariae