Untitled Quiz

Invertebrate Worms

• Worms are eukaryotic, multicellular animals, usually with digestive, circulatory, nervous, excretory, and reproductive systems.
• Worms are triploblastic with endoderm, mesoderm, and ectoderm layers.
• They exhibit bilateral symmetry, having a head and tail, with differentiated tissues.
• Some parasitic forms have multiple hosts.

Worm Specializations

• Some parasitic worms have suckers, hooks, or lips for attachment to hosts.
• Some have digestive systems to absorb nutrients from the host's food, body fluids, or tissues.
• They have a reduced nervous system.
• Locomotory organs may be reduced or absent.
• Sexes might be separate or fused (hermaphrodite).
• Reproductive systems might be complex.
• The worms can produce hundreds or thousands of eggs.

Worm Classification (Phyla)

• Platyhelminthes (Flatworms):

  • Acoelomates (lack body cavity) with thin, solid bodies.
  • Bilateral symmetry
  • Approximately 14,500 species
  • Free-living (e.g., planarians) or parasitic (e.g., flukes and tapeworms).

• Nematoda (Roundworms):

  • Pseudocoelomates (false body cavity)
  • Bilateral symmetry.

• Annelida (Segmented Worms):

  • Coelomates (true body cavity)

Flatworms (Platyhelminthes)

• Class Turbellaria (Planarians)

  • Free-living, mostly predators
  • Freshwater and some marine
  • Body size range from less than 1cm to ~60 cm
  • Possess a ciliated epidermis and move by cilia and muscle undulations.

• Class Trematoda (Flukes):

  • Leaf-shaped bodies
  • Ventral and oral suckers for attachment and nutrient intake.
  • Parasitic, with life cycles involving multiple hosts.
    • Often have two or more hosts with one as the final host in order to complete the life cycle and reproduce.
    • Classified according to the host tissues in which adult lives. (e.g., blood flukes, liver flukes)

• Class Cestoda (Tapeworms):

  • Long, flat bodies that are intestinal parasites.
  • Lack a digestive system and absorb food from the host through a cuticle.
  • Hermaphrodite
  • Body divided into proglottids where the reproductive organs reside.
  • Gravid proglottids contain numerous eggs.
  • Have scolex for attachment to the intestinal wall.

Liver Fluke

• The adult liver fluke is leaf-like and reaches a size of 3-7cm.
• Possesses both oral and ventral suckers.
• It has a digestive system and is a hermaphrodite.
• Inhabits the bile ducts of vertebrates (sheep, goats, rabbits, etc.)
• May be fatal if host eats contaminated leaf vegetables or undercooked liver.

Blood Flukes

• Separate sexes (male and female).
• Males have a gynecophoric canal to carry female.
• Cause schistosomiasis , affecting millions globally.
• Adults live in the bloodstream, digestive tracts, or visceral organs of definitive hosts.
• Definitive hosts often include humans.
• Larva is called cercariae which invades human skin via contaminated water. Cercariae enter the circulatory system and to the abdominal and pelvic veins.

Tapeworms

• Parasitic worms having a head (scolex) with hooks and suckers for attachment
• Flattened body segments (proglottids) contain the reproductive organs
• Hermaphrodites, leading to self-fertilization or with others.
• The proglottids break off and pass out in feces, continuing the life cycle.

Helminth Life Cycle

• Often complex, with multiple hosts.
• Intermediate hosts harbor larval stages, while the definitive host houses the adult stage.
• Sexual reproduction strategies include Dioecious (separate sexes) and Monoecious (hermaphrodites).

Worm Digestion and Nutrition

• Most are carnivores, consuming small invertebrates, scavenging, or eating dead animals.
• They ingest food via the pharynx (sometimes extendable/contractible)
• Digestion is partially external and partially internal, using a gastrovascular cavity for digestion.

Worm Excretory System

• Specialized organs/cells, such as protonephridia and flame cells, are important in water regulation.
• Protonephridia are networks of tubules that draw water in the body through negative pressure caused by beating cilia in the flame cells.
• The excretory products are removed via nephridiopores.

Worm Reproduction

• Asexual reproduction (often by transverse fission) allows for rapid regeneration.
• Sexual reproduction is common, with most exhibiting internal fertilization and laying eggs in cocoons.
• Hermaphrodites may self-fertilize or cross-fertilize with others.

Worm Classification

• Platyhelminthes (flatworms) are divided into classes Turbellaria (free-living), Trematoda (parasitic flukes with intermediate hosts), and Cestoda (tapeworms).
• Nematoda (roundworms) are characterized by their pseudocoelom and lack of segmentation.
• Annelida (segmented worms) are coelomates divided into various classes (important to note the differences and not details).

Control of Schistosomiasis

• Destruction of snail hosts (intermediate hosts).
• Proper disposal of excrement to reduce contamination.
• Treatment of infected individuals.