Lab 4: Phylum Platyhelminthes (flatworms) Flashcards
What clade(s) do Phylum Platyhelminthes belong to?
Metazoa, Eumetazoa, and Bilateria
What kind of symmetry of a flatworm?
Bilateral symmetry; meaning that the animal can be divided into mirror image left and right halves by a single plane that passes along the midline of its body
What is the directional term for the head end?
anterior
What is the directional term for the tail end?
posterior
What is the directional term for the side facing up?
dorsal surface
What is the directional term for the side facing down?
ventral surface
What is the term that means worms are flattened from the top down?
Dorsoventrally flattened
What kind of movement do flatworms use?
undirectional movement
What is unidirectional movement?
moving with one part of the body primarily leading the way, identified as the anterior end
What does triploblastic mean?
development from three germ layers; the endoderm, ectoderm, and mesoderm
Platyhelminths have more ________ bodies than diploplastic animals
complex
During cleavage, the embryo is called a _______.
blastula
Where does the mesoderm layer form? (Inner, middle, outer?)
between the inner and outer layer; middle
What is the opening through which the cells move inward ?
blastopore
What does the mesoderm (middle layer) form?
muscles and loosely packed connective tissue called mesenchyme
What kind of nervous system do platyhelminthes have? What does it mean?
Centralized; consists of a mass of nerve cells (brain), and a nerve cord
What are auricles?
sensory cells that detect water currents, solid objects, and chemicals located in two flap-like projections on the head
Sensory cells in the ____ detect changes in the environment
head
Do flatworms move with purpose?
Yes, their sensory structures repond to stimuli such as food or light. They choose where to go.
What is a cilia?
hairlike structures that exist on a flatworms surface that together move too propel an organism
What does the mesenchyme do?
acts as a modified hydrostatic skeleton and is referred to as a mesenchymal hydrostatic skeleton
The planaria has what kind of digestive system?
Incomplete; one opening serves as both the mouth and anus
What is the feeding strategy of most free-living flatworms?
carnivorous predators (hunt other animals) or scavengers (find and eat dead animals)
What is asexual reproduction?
the animal splits in two parts and then through regeneration, grow two whole organisms. The two individuals are genetically identical to one another
What is a hermaphrodite?
each individual has both ovaries and testes
Do flatworms fertilize their own eggs?
No, they exchange sperm with another worm
What are two endoparasites?
-flukes
-tapeworms
What is a definitive host?
the host in which sexual reproduction occurs
What is an intermediate host
host in which additional development occurs, but maturation and sexual reproduction do not occur
Is Mesenchyme a non-living tissue.
No, it is made up of cells and considered to be living (unlike mesohyl and mesoglea)
The part of the free-living flatworm’s body that distributes ingested nutrients to all parts of the body is the:
Gastrovascular cavity
T/F: An animal that feeds by predation (hunting food) does not require a centralized nervous system
False
Which of the following is true about the way gas exchange constrains the body plans of a sponge, an anemone, and a free-living flatworm?
A sponge and anemone are constrained to each layer of the body wall being only one cell thick, while a flatworm is constrained to having a body plan that has a very high surface area to volume ratio by being very flat and thin.
Can triploblasts only have incomplete digestive tracts?
No, some can have complete and others can have incomplete.
What gives the flatworm shape and support?
the mesanchyme and body wall
What are the steps involved in getting nutrients to the cells?
- obtaining food by scavenging or predation
- chemical digestion by the gastrodermis secreting digestive enzymes, then the food being digested in the GVC
- getting rid of undigested material
What makes it possible to distribute food to the large surface area of a flatworm?
The highly branched GVC
What helps a flatworm locate food?
Chemoreceptors
What ingests the food in flatworms?
the pharnyx
If an animal increases in size, the volume increases faster than the surface area, because volume is cubed while surface area is squared. So as volume increases, surface area to volume ratio decreases. Why is this significant for animals doing gas exchange?
When there is more volume and less surface area, the slow process of diffusion cannot occur at a rate fast enough to keep all cells alive.
What is a flatworms solution to the surface area to volume dilemma?
By increasing the surface area to volume by being very flat, flatworms provide an extensive surface area for the volume of living cells and can provide oxygen at a rate that keeps up with the demand
What is the nitrogenous waste in flatworms?
Ammonia
What is asexual reproduction?
production of offspring from a single parent that occurs without the fusion of gametes; offspring are genetically identical
What is the cost of hermaphroditism?
Energy expenditure
What is the benefit of hermaphroditism?
They can reproduce with any planaria, not just male or female but either
What is a tegument in a fluke and tapeworm?
tegument replaces the epidermis in larva and protect from hosts digestive enzymes and once cells fuse, there is no membrane between them so fewer ways for immune system or digestive enzymes to hurt them
What are the bristle like projections in flukes and what do they do?
Spines; they help anchor themselves to host tissues
What are the projections in tapeworms and what to they do?
microvilli; they increase surface area so more surface area more absorption of the already digested nutrients from the host’s digestive system
What is the anterior end of a tapeworm called?
scolex; they also have suckers
The segments in tapeworms are called
proglottids generated behind the scolex
Mature proglottids
when proglottids mature and develop testes and ovaries
Gravid proglottids
egg and sperm fuse forming fertilized eggs; at posterior end and break off and leave the definitive host with the feces and an intermediate host will ingest them
What strategy do flukes use to increase the number of offspring produced and where does it occur in the life cycle?
they use asexual reproduction to increase offspring , occurring in the intermediate host during their life cycle
What strategy do tapeworms use to increase the number of offspring produced?
They produce a large number of eggs using a segmented body structure to release them, enhancing survival chances
