Platyhelminthes - Zoology

What body plans can be found in phylum Platyhelminthes?

Acoelomate - without a body cavity

What tissue structure is found in flat worms?

Triploblastic - three embryonic germ layers

What is the ectoderm?

Outer layer that gives rise to skin tissue and associated structures.

What is the endoderm?

Inner layer that gives rise to the gut lining and associated structures.

What is the mesoderm?

Inner layer that gives rise to true muscle tissue, most organ systems and bones, connective tissue.

What layer is #1?

Ectoderm

What layer is #2?

Parenchyma (mesoderm)

What layer is #3?

Mesodermal Organ

What layer is #4?

Gut (endoderm)

What is the parenchyma?

Connective tissue with living cells. (Cellular material between epidermis and gastrodermis).

What do adult platyhelminths body plans consist of?

Bilateral symmetry, anterior, posterior, dorsal, ventral, and lateral surfaces

Cephalization occurs in what species?

Free-living

Why is cephalization common in certain species?

Prominent in animals that search for food as cephalization helps them search for food.

How is the body flattened?

Dorso-ventrally (top-bottom)

What is #1?

Auricle (sensory structures)

What is #2?

Eye spots

What is #3?

Head

What is #4?

Mouth

What is platyhelminthes’ level of organization?

Organ system (due to presence of mesoderm)

What digestive system type do flat worms have?

Incomplete

What makes it an incomplete digestive system?

Mouth but no anus

What is the only subphylum that lost it’s digestive system (secondary characteristic)?

Tapeworms

Why do tapeworms have elaborate skin texturing?

More surface area allowing for greater absorption.

Tapeworm skin is…

Syncytial with microtriches (hair-like microvilli)

Freshwater flatworms have what type of nervous system?

Ladder-type (one pair of lateral nerve cords connected to cerebral ganglia)

Flatworms typically have ____ nerve cords, with _______ and _____-______

paired, lateral, cross nerves

Osmoregulation is carried out by what?

Flame cells

What are flame cells?

Lined with cilia that drive fluids through a series of tubules which open to outside through a series of pores.

How does gas exchange occur in flatworms?

Simple diffusion, their flattened bodies aide in this process (make it easier for diffusion due to high surface area to volume ratio).

Class Turbellaria are…

Free-living flatworms

Class Monogenea are…

Small flukes, ectoparasites on fishes

Class Trematoda are…

Larger flukes, endoparasites

Class Cestoda are…

Tapeworms, endoparasites

Class Turbellaria…

Digestive system = Y-shaped with eversible (can be turned inside out or extended) pharynx for feeding.

Sexual reproduction is via what in Dugesia?

Complex organ system (syngamy)

How is asexual reproduction performed in Dugesia?

Fission (autofragmentation)

Are Dugesia monoecious or dioecious?

Monoecious