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CSU-PUEBLO / Biology / BIOL 202 / What is torsion?

What is torsion?

What is torsion?

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Zoology Exam 2 study guide


What is torsion?



1. Name the defining ancestral characteristics of Phylum Mollusca. Mantle- sheath of skin that extends from visceral mass and hangs  down on each side

Mantle cavity- space between visceral mass and mantle, has the gills Muscular foot- for locomotion and attachment. EX: mucous of a snail Radula- ribbon like row of teeth

2. What is torsion? What is one advantage of torsion?

Torsion is the rotation of the visceral mass, mantle, and shell 180˚ with  respect to the head and foot of the gastropod. This rotation brings the  mantle cavity and the anus to an anterior position above the head. The head enters the shell first. Therefore, it does not expose the head to  predators.

Anterior opening of the mantle cavity allows clean water to enter into the  mantle cavity front the front of the snail.


What is one advantage of torsion?



3. Both bivalves and octopuses have multiple types of muscles in  their body, besides the “foot”. What is the foot used for in each  class (bivalves and cephalopods)? We also discuss several other topics like Does the strength of electric field due to an infinite long line charge depend upon the distance of the observation point from the line charge?

Bivalves-use the foot by contracting and relaxing it to burrow  Octopus (cepholo)- divided in tentacles for suction cups or hooks for  capturing prey

4. You find shells from two different species of bivalves that have  different growth rates but are the same size (i.e., one grows more  quickly than the other). However, one has a very thick shell and one  has a very thin shell. Which do you think is older?

5. Why do you think cephalopods, but not bivalves have closed circulatory  systems?

They need closed circulatory systems in order to move rapidly. It allows oxygen and nutrients to go to specific areas of the body in need.


What are metameres?



1. What are metameres? Do you think this is a type of segmentation (broader term used across phyla)?

Similar body segments arranged in a linear series. Yes.

2. Polychaetes can be both errant or sedentary feeders. How do  their feeding structures differ?

Errant- have foregut midgut and hindgut. Usually predators and scavengers. Sedentary- Feed on suspended particles and debris in sediment. Well  developed head and cliteum.  We also discuss several other topics like Which of the two types of needs is most important to satisfy?

3. What mode of reproduction do earthworms use?  

Cross fertilization- both worms excrete so much mucous, that what is called a slime tube forms around their bodies. Each worm ejaculates sperm from its  sex organs into this slime tube and it is then deposited in the other worm's  sperm receptacle.

4. Name one organ system that is NOT arranged in metameres in an  earthworm.

Digestive tract.

5. Are leeches or earthworms better examples of segmentation?  Why?

Leeches- they have 34 segments.

1. What is arthropodization?  

Stiffening of chitonous cuticle (calcium) to form jointed exoskeleton. The  evolution that occurred- reduced coelom, no cilia, open system of sinuses. We also discuss several other topics like What is the meaning of spring potential energy?
We also discuss several other topics like How does carrying capacity affect logistic growth?
We also discuss several other topics like What type of learning associates a stimulus with a response?
We also discuss several other topics like What is the dynamic nature of chemical equilibria?

2. What are the four major subphyla of Phylum Arthopoda? For each  subphylum, give one example of a species in that Phylum.

Crustacaea- crab

Chelicerata- tick

Myriapoda- centipede

Hexapoda- Loose

3. Arachnids (e.g., spiders) have malpighian tubules. What are they  used for? How many times did they evolve in Arthropoda?

These tubules are used to excrete nitrogenous waste. Between mid and hind  gut. Evolved 2 times.

4. Name five species (or types of species) that all belong to  subphylum Crustacea.

Barnacles, crawfish, crayfish, crab, amphipod.

5. Describe the main features of a crustacean’s circulatory system. Hemocoel: body cavity

Open system

Heart- single chamber of striated muscle

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