Untitled Quiz

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.

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.

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)

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.

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.

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).

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.

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.

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.

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).