Chapter 9-Worms (Platyhelminthes, Nematoda, and Annelida) Flashcards
What does it mean to be a bilateral organism?
only one plane of bisection produces left and right mirror-image halves; body is polarized along 2 perpendicular axes: anterior-posterior (head-tail) axis and dorsal-ventral (back-belly) axis
What are the 3 phyla of worms studied in lab and their common names?
Platyhelminthes (flatworms), Nematoda (roundworms), Annelida (segmented worms)
What does it mean to be triploblastic?
have 3 embryonic layers: 1. ectoderm 2. mesoderm 3. endoderm
What does the ectoderm give rise to?
covering of animal
What does the mesoderm give rise to?
forms muscles and most other organs between gut and outer covering
What does the endoderm give rise to?
lining of digestive tract
What does it mean to be acoelomate and what kind of worm exhibits this?
lack internal body cavity, apart from incomplete digestive trace; flatworms
What does it mean to be pseudocoelomate and what kind of worm exhibits this?
body cavity located between mesoderm and endoderm; roundworms
What doe it mean to have a true coelom and what kind of worm exhibits this?
body cavity that develops entirely within the mesodermal layer; annelids
What are animals with a true coelom called?
coelomates or eucoelomates
T/F The presence and configuration of a body cavity was a key innovation in animal body design.
True
T/F A body cavity serves as a hydrostatic skeleton.
True
How is a hydrostatic cavity useful?
muscular contractions to displace fluid within a cavity, therefore exerting force and changing the shape of the cavity
What are some general characteristics of flatworms?
mostly small, dorsoventrally flattened, soft-bodied worms that live in aquatic environments; considered simplest of Bilateria; acoelomate, lack a circulatory system, most are monoecious and exert hermaphroditism, exhibit regeneration
Do flatworms exhibit some form of cephalization?
yes
Are many flatworms parasitic?
yes
What types of flatworms are parasitic?
flukes and tapeworms
Where do Turbellarians live?
marine environments, some inhabit fresh water or moist soils, some prefer sand, mud, or under stones and shells where they scavenge and hunt for small animals
T/F Turbellarians are free-living worms.
True
T/F Turbellarians are not hermaphroditic.
False-most are hermaphroditic
How does reproduction occur in Turbellarians?
copopulation and cross fertilization
What are some characteristics of Dugesia?
acoelomates, found in freshwater habitats, known as planaria, uses a pharynx to eat, head has lateral lobes and light-sensitive eyespots
What is the pharynx?
food sucked up through tube to mouth and leads to a blind gastrovascular cavity with 3 lobes, one anterior and two posterior; muscular organ usually retracted in body but can be everted through mid ventral opening
How do flatworms move?
use cilia on outside surface for movement
What clade/class do Turbellarians belong to?
Turbellaria
What are trematodes also called?
flukes
What are flukes known for doing?
parasitize vertebrates including humans
What are endoparasites?
live inside host
What are ectoparasites?
parasitize surface of host
What important adaptation do endoparasites have?
metabolically active epicuticle resists host’s digestive enzymes and immune defenses
How does a fluke attach to its host?
suckers that are located along midline; the anterior sucker surrounds the mouth
Explain the life cycle of a trematode.
Involves 2 or more hosts: first intermediate host typically a gastropod mollusk (snail), second intermediate host an arthropod or fish, vertebrate is always the final or definitive host
What is the life cycle of a fluke?
zygote > miracidium > sporocyst > redia > cercaria > metacercaria (absent in blood flukes such as Schistosoma) > adult; produce a large amount of eggs
What is the Fasciola hepatic commonly known as?
sheep liver fluke