Lecture 5 - Phylum Platyhelminthes

Question 1

What is the defining characteristic of parasitic Platyhelminthes?

Answer 1

The syncytial tegument (neodermis), a non-ciliated layer that protects against host digestive enzymes and immune responses

Question 2

What are the four classes within Phylum Platyhelminthes?

Answer 2

Turbellaria, Trematoda, Monogenea, and Cestoda

Question 3

What is the function of the dual-gland adhesive organ in Turbellarians?

Answer 3

It allows for temporary attachment to surfaces using viscid gland cells for adhesion and releasing gland cells for detachment

Question 4

What is the primary mode of movement in Turbellaria?

Answer 4

Movement is facilitated by alternating contractions of circular and longitudinal muscles, aided by cilia on the ventral surface

Question 5

How do Turbellarians protect themselves using rhabdites?

Answer 5

Rhabdites swell and form a protective mucous sheath around the body

Question 6

What specialized cells are found in the protonephridia for osmoregulation in Platyhelminthes?

Answer 6

Flame cells, which have tufts of flagella to move fluid through the tubules for excretion

Question 7

What is the main function of the muscular pharynx in Turbellarians?

Answer 7

The pharynx contracts to extend and retract, allowing the worm to ingest food

Question 8

How do parasitic Platyhelminthes differ from Turbellarians in their body covering?

Answer 8

Parasitic forms have a syncytial tegument instead of a ciliated epidermis

Question 9

What is the role of the branched digestive system in Turbellarians?

Answer 9

The branched system increases surface area for digestion and nutrient absorption

Question 10

How do Monogenea attach to their hosts?

Answer 10

Using a specialized structure called an opisthaptor, which is equipped with hooks, suckers, or clamps

Question 11

What is the primary function of the flame cells in the Platyhelminthes excretory system?

Answer 11

Flame cells regulate water balance and remove metabolic waste through protonephridia

Question 12

How do Trematoda (flukes) feed?

Answer 12

They use an oral sucker to attach to the host and a muscular pharynx to pump food into their digestive system

Question 13

What are proglottids in Cestoda (tapeworms)?

Answer 13

Segments that make up the body of a tapeworm, each containing reproductive organs

Question 14

What is the function of the scolex in tapeworms?

Answer 14

It is the attachment organ used to anchor the tapeworm to the host’s intestinal wall

Question 15

How do tapeworms absorb nutrients?

Answer 15

Through microtriches, which are finger-like projections on their tegument that increase surface area for nutrient absorption

Question 16

How do tapeworms reproduce?

Answer 16

They are monoecious, with each proglottid containing both male and female reproductive organs, allowing cross-fertilization or self-fertilization

Question 17

What type of larvae do Monogenea produce?

Answer 17

Ciliated larvae called oncomiracidia, which hatch and swim to find a new host

Question 18

How do parasitic Platyhelminthes protect themselves inside their hosts?

Answer 18

Their syncytial tegument protects against the host’s digestive enzymes and immune responses

Question 19

What is the function of the parenchyma in Turbellaria?

Answer 19

It acts as packing tissue
-provides structural support
-contains cells and fibers for body shape maintenance

Question 20

What do scientists believe about the evolutionary history of Platyhelminthes?

Answer 20

They may have evolved from ancestors with cnidarian-like characteristics;
-mesoglea layer (later replaced by mesodermal-derived parenchyma)

Question 21

Why is the evolution of a branched digestive system significant in Turbellarians?

Answer 21

Allows for more efficient distribution of nutrients throughout the body

Question 22

How do Platyhelminthes, including Turbellaria, respire?

Answer 22

They rely on diffusion across their body surface to exchange gases with their environment

Question 23

What is the structure of the nervous system in more primitive Platyhelminthes?

Answer 23

• have a subepidermal nerve plexus, (similar to the nerve net in Cnidarians)

Question 24

What sense organs are found in Turbellarians?

Answer 24

Have tactile and sensory cells spread across the body
- ocelli for detecting light
-statocysts for balance
- rheoreceptors for detecting water currents

Question 25

What is the role of the ciliated epithelium in free-living Turbellarians?

Answer 25

Aids in movement
-allowing them to glide over surfaces with help of secreted mucus

Question 26

How does the life cycle of Monogenea typically proceed?

Answer 26

Adults release eggs that hatch into ciliated oncomiracidium larvae, which swim to find a new host

Question 27

What happens to the reproductive organs of tapeworm proglottids as they mature?

Answer 27

The reproductive organs degenerate, and the proglottid becomes a “bag of eggs” before breaking off and leaving the host.

Question 28

What is the role of intermediate hosts in the Trematoda life cycle?

Answer 28

Immature stages of flukes can be found in vertebrates, invertebrates, or plants, which serve as intermediate hosts before the parasite infects its final host.

Question 29

Why are tapeworms considered an example of evolution resulting in simplification?

Answer 29

Due to their adaptation to the stable environment of the host’s intestine, tapeworms have lost many complex structures found in their ancestors