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BIO 101 Exam #2 Prep Mollusks, Segmented Worms, & Basal Ecdysozoans
Terms in this set (21)
soft extension of the body wall in mollusks that secretes the shell
hard mouthparts of mollusks that often are developed as a rasping tongue
foot (in terms of mollusks)
muscular organ in mollusks that is used for movement
muscle found in bivalve mollusks that pulls the two valves together (closes shell)
bristles in annelids that anchor the body and aid in movement
thickened region of certain segments in many earthworms and leeches that secretes mucus during reproduction
hard carbohydrate that forms the exoskeleton and cuticle of several bilaterian clades
shedding (molting) of outer, non-cellular cuticle layer; characteristic of Ecdysozoa
What feature(s) make a snail a protostome bilaterian animal?
Snails (gastropod mollusks) are protostomes in that they exhibit a blastopore (first opening) that develops into the mouth and the nerve cord is positioned ventrally (along the belly side of the animal). Snails are bilaterians in that they are bilaterally symmetrical (divided into right and left halves), are cephalized (have a distinct head with a centralized nervous system), and have triploblastic tissues (three tissue layers). Snails are animals in that they are multicellular eukaryotic organisms, heterotrophic, obtain nutrients through ingestion, and have collagen.
What feature(s) make an earthworm a protostome bilaterian animal?
Earthworms (annelids) are protostomes in that they exhibit a blastopore (first opening) that develops into the mouth and the nerve cord is positioned ventrally (along the belly side of the animal). Earthworms are bilaterian in that they are bilaterally symmetrical (divided into right and left halves), are cephalized (have a distinct head with a centralized nervous system), and have triploblastic tissues (three tissue layers). Earthworms are animals in that they are multicellular eukaryotic organisms, heterotrophic, obtain nutrients through ingestion, and have collagen.
List the major synapomorphies of Mollusca
mantle, calcareous shell, muscular "foot", chambered heart, radula, and posterior gills.
List the major synapomorphies of Annelida
metameric segmentation and setae
List the major synapomorphy of Ecdysozoa
ecdysis (shedding of outer, non-cellular cuticle layer)
Which major clade of mollusk is the most diverse in terms of the greatest number of species?
There is only one clade of mollusk that includes fully terrestrial (land dwelling) species. Which clade is it?
only some members of Gastropoda are fully terrestrial
Bivalve molluks have lost their radula. How do they eat?
Bivalve mollusks eat through suspension feeding.
They draw water with food particulates into their viscaeral masses through incurrent siphons, which directs the water over the gills. Food is trapped in the gills and moved to the mouth, and water is expelled through excurrent siphons.
Do "worms" (Platyhelminthes, Annelida, Nematoda, and Onycophora) form a monophyletic group?
Animals that often are called "worms" do not form a monophyletic group, which is an ancestor and all of its descendents. Annelids and platyhelminths are more closely related to mollusks than they are to nematodes, and nematodes are more closely related to arthropods than they are to either annelids or platyhelminths. (FYI, the most recent common ancestor of Platyhelminthes, Annelida, and Nematoda is at Protostomia, but not all protostomes would be considered "worms".)
Annelids have metameric segmentation. What does that mean?
division of the body into serial parts divided by septa
The segments are easily observed in lumbricid annelids (earthworms)
Briefly discuss the lifestyle(s) of nematodes. Are they free-living, symbiotic, or parasitic?
Nematodes can be free-living (such as the model organism C. elegans), mutualistic (such as species that live in the intestines of iguanas to help digest plant material), OR parasitic (such as round worms, hook worms, and pin worms)
What feature does members of Onycophora share with members of Tardigrada, but not with Nematoda?
Onycophora (velvet worms) and Tardigrada (water bears) possess unjointed appendages, but appendages are absent in Nematoda. In addition, the exoskeletons of onycophorans and tardigrades are composed of chitin, but the exoskeleton of nematodes is composed of collagen
What is cryptobiosis, and how has it led to the success of tardigrades?
a state of suspended animation observed in tardigrades, and it is characterized by a nearly complete drying of the body and a stop of metabolism
It allows tardigrades to survive if the film of water in which they live dries, and it also allows them to survive extremely low temperatures, and even the vacuum of space!
Recommended textbook explanations
Johnson, Peter H. Raven
Miller and Levine Biology
Joseph S. Levine, Kenneth R. Miller
Modern Biology: Student Edition
Janet L. Hopson, Postlethwait
Biology The Dynamics of Life
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