Lecture 5 - Phylum Platyhelminthes Flashcards
What is the defining characteristic of parasitic Platyhelminthes?
The syncytial tegument (neodermis), a non-ciliated layer that protects against host digestive enzymes and immune responses
What are the four classes within Phylum Platyhelminthes?
Turbellaria, Trematoda, Monogenea, and Cestoda
What is the function of the dual-gland adhesive organ in Turbellarians?
It allows for temporary attachment to surfaces using viscid gland cells for adhesion and releasing gland cells for detachment
What is the primary mode of movement in Turbellaria?
Movement is facilitated by alternating contractions of circular and longitudinal muscles, aided by cilia on the ventral surface
How do Turbellarians protect themselves using rhabdites?
Rhabdites swell and form a protective mucous sheath around the body
What specialized cells are found in the protonephridia for osmoregulation in Platyhelminthes?
Flame cells, which have tufts of flagella to move fluid through the tubules for excretion
What is the main function of the muscular pharynx in Turbellarians?
The pharynx contracts to extend and retract, allowing the worm to ingest food
How do parasitic Platyhelminthes differ from Turbellarians in their body covering?
Parasitic forms have a syncytial tegument instead of a ciliated epidermis
What is the role of the branched digestive system in Turbellarians?
The branched system increases surface area for digestion and nutrient absorption
How do Monogenea attach to their hosts?
Using a specialized structure called an opisthaptor, which is equipped with hooks, suckers, or clamps
What is the primary function of the flame cells in the Platyhelminthes excretory system?
Flame cells regulate water balance and remove metabolic waste through protonephridia
How do Trematoda (flukes) feed?
They use an oral sucker to attach to the host and a muscular pharynx to pump food into their digestive system
What are proglottids in Cestoda (tapeworms)?
Segments that make up the body of a tapeworm, each containing reproductive organs
What is the function of the scolex in tapeworms?
It is the attachment organ used to anchor the tapeworm to the host’s intestinal wall
How do tapeworms absorb nutrients?
Through microtriches, which are finger-like projections on their tegument that increase surface area for nutrient absorption
How do tapeworms reproduce?
They are monoecious, with each proglottid containing both male and female reproductive organs, allowing cross-fertilization or self-fertilization
What type of larvae do Monogenea produce?
Ciliated larvae called oncomiracidia, which hatch and swim to find a new host
How do parasitic Platyhelminthes protect themselves inside their hosts?
Their syncytial tegument protects against the host’s digestive enzymes and immune responses
What is the function of the parenchyma in Turbellaria?
It acts as packing tissue
-provides structural support
-contains cells and fibers for body shape maintenance
What do scientists believe about the evolutionary history of Platyhelminthes?
They may have evolved from ancestors with cnidarian-like characteristics;
-mesoglea layer (later replaced by mesodermal-derived parenchyma)
Why is the evolution of a branched digestive system significant in Turbellarians?
Allows for more efficient distribution of nutrients throughout the body
How do Platyhelminthes, including Turbellaria, respire?
They rely on diffusion across their body surface to exchange gases with their environment
What is the structure of the nervous system in more primitive Platyhelminthes?
- have a subepidermal nerve plexus, (similar to the nerve net in Cnidarians)
What sense organs are found in Turbellarians?
Have tactile and sensory cells spread across the body
- ocelli for detecting light
-statocysts for balance
- rheoreceptors for detecting water currents
What is the role of the ciliated epithelium in free-living Turbellarians?
Aids in movement
-allowing them to glide over surfaces with help of secreted mucus
How does the life cycle of Monogenea typically proceed?
Adults release eggs that hatch into ciliated oncomiracidium larvae, which swim to find a new host
What happens to the reproductive organs of tapeworm proglottids as they mature?
The reproductive organs degenerate, and the proglottid becomes a “bag of eggs” before breaking off and leaving the host.
What is the role of intermediate hosts in the Trematoda life cycle?
Immature stages of flukes can be found in vertebrates, invertebrates, or plants, which serve as intermediate hosts before the parasite infects its final host.
Why are tapeworms considered an example of evolution resulting in simplification?
Due to their adaptation to the stable environment of the host’s intestine, tapeworms have lost many complex structures found in their ancestors
