Question 1

Of what evolutionary significance is the "hydrostatic skeleton"?

Accepted Answer

The hydrostatic skeleton is of significant evolutionary importance as it represents a fundamental mechanism by which many organisms have achieved movement, support, and structural integrity. This type of skeleton is characterized by a fluid-filled cavity, the coelom, surrounded by muscles. Unlike rigid skeletons, hydrostatic skeletons rely on the pressure of the fluid inside the body cavity to maintain shape and enable movement.

Here are some key evolutionary significances of the hydrostatic skeleton:

1. **Early Evolution of Movement**: The hydrostatic skeleton allowed the earliest multicellular organisms to move in a coordinated manner. By contracting muscles against the fluid-filled cavity, these organisms could change shape and propel themselves through their environment. This was a significant step in the evolution of more complex locomotion.

2. **Support and Structure**: For soft-bodied organisms, the hydrostatic skeleton provides structural support without the need for hard, mineralized tissues. This allows for a wide range of body shapes and sizes, which can be advantageous in different ecological niches.

3. **Adaptability**: Hydrostatic skeletons are highly adaptable. They can change shape easily, allowing organisms to squeeze through tight spaces or burrow into substrates. This flexibility is advantageous for escaping predators, hunting prey, or simply moving through complex environments.

4. **Energy Efficiency**: Hydrostatic skeletons can be energy-efficient because they do not require the organism to maintain a rigid structure at all times. Muscles can relax when not in use, saving energy.

5. **Evolution of Complex Organisms**: The hydrostatic skeleton has been a stepping stone in the evolution of more complex body plans. For example, the ancestors of cephalopods (like squids and octopuses) and annelids (like earthworms) utilized hydrostatic skeletons. These groups have since evolved a variety of sophisticated adaptations, such as the ability to manipulate objects and complex burrowing behaviors.

6. **Diversification**: Hydrostatic skeletons have allowed for a great diversification of life forms, particularly among invertebrates. Many phyla, including Cnidaria (jellyfish), Annelida (segmented worms), and Mollusca (mollusks), rely on this type of skeletal system.

7. **Evolutionary Precursor**: In some lineages, the hydrostatic skeleton may have been a precursor to the development of more rigid internal or external skeletons. For example, the notochord in chordates, a flexible rod-like structure, is considered a type of hydrostatic skeleton that played a role in the evolution of the vertebral column in vertebrates.

In summary, the hydrostatic skeleton has played a crucial role in the evolution of multicellular life, particularly in soft-bodied organisms. It has facilitated movement, provided structural support, allowed for adaptability in various environments, and served as a precursor to more complex skeletal systems. Its significance is evident in the diversity and success of the myriad organisms that utilize this form of skeletal structure.

Question 2

When earthworms mate,the _______________ secretes mucus to hold them together.

Accepted Answer

clitellum

Question 3

The circulatory system in the earthworm

Accepted Answer

A) is absent since all respiration is across the epidermis. 
B) is an open system where hemolymph washes through body sinuses. 
C) has a dorsal vessel as the main pumping organ. 
D) has no pumping structure but depends on the action of body muscles to move the blood. 
E) has five pumps that circulate blood first to the gills and then to the rest of the body. 
A) is absent since all respiration is across the epidermis. 
B) is an open system where hemolymph washes through body sinuses. 
C) has a dorsal vessel as the main pumping organ. 
D) has no pumping structure but depends on the action of body muscles to move the blood. 
E) has five pumps that circulate blood first to the gills and then to the rest of the body. C

Question 4

The remaining valid use of "medicinal leeches" is to

Accepted Answer

A) apply them to severely-bruised tissue to relieve blood congestion and allow damaged vessels to grow back. 
B) use them to clean out dead tissue from a wound. 
C) use them to restore the balance of body fluids or humors. 
D) apply them to increase circulation or blood flow to a region. 
E) All of the choices are correct. 
A) apply them to severely-bruised tissue to relieve blood congestion and allow damaged vessels to grow back. 
B) use them to clean out dead tissue from a wound. 
C) use them to restore the balance of body fluids or humors. 
D) apply them to increase circulation or blood flow to a region. 
E) All of the choices are correct.

Question 5

Why does the wound from the bite of a leech bleed profusely?

Accepted Answer

The wound from the bite of a leech bleed

Question 6

A unique feature of the leech nervous system is that

Accepted Answer

A) leeches have good eyesight. 
B) leeches have two "brains";one anterior and one posterior. 
C) they can join their nervous system with the nerves in the host tissue. 
D) it only has giant axons that provide fast responses. 
E) the nerve ladder and ganglia are all dorsal. 
A) leeches have good eyesight. 
B) leeches have two "brains";one anterior and one posterior. 
C) they can join their nervous system with the nerves in the host tissue. 
D) it only has giant axons that provide fast responses. 
E) the nerve ladder and ganglia are all dorsal.

Question 7

Discuss why segmentation is such an important innovation in the Annelida.

Accepted Answer

Segmentation is a crucial innovation in

Question 8

In leeches,a cocoon into which fertilized eggs will be deposited is secreted by the __________.

Accepted Answer

The answer of In leeches,a cocoon into which fertilized eggs...

Question 9

The body wall of an annelid consists of

Accepted Answer

A) an epidermis and longitudinal muscles only,as is the case with nematodes. 
B) a non-living cuticle,and inner circular muscles to squeeze the cuticle. 
C) an epithelium that secretes cuticle,and layers of both longitudinal and circular muscles. 
D) a bare epidermis with inner circular muscles and outer longitudinal muscles. 
E) a soft exoskeleton to hold up in the absence of inner fluids,with outer circular muscles and inner longitudinal muscles. 
A) an epidermis and longitudinal muscles only,as is the case with nematodes. 
B) a non-living cuticle,and inner circular muscles to squeeze the cuticle. 
C) an epithelium that secretes cuticle,and layers of both longitudinal and circular muscles. 
D) a bare epidermis with inner circular muscles and outer longitudinal muscles. 
E) a soft exoskeleton to hold up in the absence of inner fluids,with outer circular muscles and inner longitudinal muscles.

Question 10

Each internal compartment of an annelid is lined with

Accepted Answer

A) amebocytes that serve to distribute food and remove wastes. 
B) nephridiocytes that keep the coelomic fluid in circulation. 
C) cuticle secreted by the epithelium. 
D) peritoneum,a layer of ectodermal epithelium. 
E) peritoneum,a layer of mesodermal epithelium. 
A) amebocytes that serve to distribute food and remove wastes. 
B) nephridiocytes that keep the coelomic fluid in circulation. 
C) cuticle secreted by the epithelium. 
D) peritoneum,a layer of ectodermal epithelium. 
E) peritoneum,a layer of mesodermal epithelium.

Question 11

The most recent molecular evidence suggests that the Annelida and Mollusca are more closely related to each other (in the clade Lophotrochozoa)rather than either phylum is to the Arthropoda (clade Ecdysozoa).Do you think 1)it matters that this distinction is made,and 2)should the use of molecular evidence by itself be the sole means of distinguishing the affinities of these groups? Support your argument.

Accepted Answer

1) Yes, it does matter that this distinc

Question 12

Paired appendages used for locomotion in polychaetes are called ___________________.

Accepted Answer

The answer of Paired appendages used for locomotion in polychaetes...

Question 13

The spaces in the coelom of leeches are called the _______________.

Accepted Answer

The answer of The spaces in the coelom of leeches...

Question 14

A leech

Accepted Answer

A) has a clitellum only during the breeding season. 
B) has a fixed number of segments. 
C) has both anterior and posterior suckers. 
D) has a coelomic cavity filled with connective tissue. 
E) All of the choices are correct. 
A) has a clitellum only during the breeding season. 
B) has a fixed number of segments. 
C) has both anterior and posterior suckers. 
D) has a coelomic cavity filled with connective tissue. 
E) All of the choices are correct.

Question 15

Why do zoologists not have a well-accepted theory for the origin of segmentation?

Accepted Answer

The origin of segmentation in animals is

Question 16

The circulatory system of earthworms is

Accepted Answer

A) closed with hearts pumping blood to the anterior arteries and veins returning from the posterior. 
B) open with blood "washing" through the coelomic cavity. 
C) half closed with hearts pushing blood toward the head but washing posteriorly through an open cavity. 
D) closed with dorsal and ventral blood vessels joined by five paired "hearts" forcing circulation flow dorsal-ventrally. 
E) absent and they rely solely on diffusion to absorb gases through the epidermis. 
A) closed with hearts pumping blood to the anterior arteries and veins returning from the posterior. 
B) open with blood "washing" through the coelomic cavity. 
C) half closed with hearts pushing blood toward the head but washing posteriorly through an open cavity. 
D) closed with dorsal and ventral blood vessels joined by five paired "hearts" forcing circulation flow dorsal-ventrally. 
E) absent and they rely solely on diffusion to absorb gases through the epidermis.

Question 17

In the earthworm,the typhlosole

Accepted Answer

A) is the organ of locomotion. 
B) increases the absorptive area of the gut. 
C) grinds the food. 
D) produces secretions during mating. 
E) coordinates the contractions of the digestive system. 
A) is the organ of locomotion. 
B) increases the absorptive area of the gut. 
C) grinds the food. 
D) produces secretions during mating. 
E) coordinates the contractions of the digestive system.

Question 18

A biologically plausible reason that burrowing earthworms have solid segmental walls but nonburrowing and parasitic annelids often have partial septa is

Accepted Answer

A) the segmentation was selected to enable better expansion during burrowing.Parasitic annelids do not burrow and the loss of the ability to expand segments was not disadvantageous during their evolution. 
B) the nonburrowing worms were primitive and had not yet developed full walls. 
C) nonburrowing worms are halfway between roundworms and fully-segmented earthworms. 
D) that it permits fragmentation and regeneration of body parts,which earthworms need because they are in a dangerous environment,but internal parasites do not need this. 
E) None of the choices is correct. 
A) the segmentation was selected to enable better expansion during burrowing.Parasitic annelids do not burrow and the loss of the ability to expand segments was not disadvantageous during their evolution. 
B) the nonburrowing worms were primitive and had not yet developed full walls. 
C) nonburrowing worms are halfway between roundworms and fully-segmented earthworms. 
D) that it permits fragmentation and regeneration of body parts,which earthworms need because they are in a dangerous environment,but internal parasites do not need this. 
E) None of the choices is correct.

Question 19

In the earthworm,food is drawn into the mouth by the pumping action of the _____________.

Accepted Answer

The answer of In the earthworm,food is drawn into the...

Question 20

Select the list of characteristics typical of annelids.

Accepted Answer

A) Segmentation,open circulation,and metanephridia 
B) Segmentation,a closed circulatory system,and metanephridia 
C) An exoskeleton,metanephridia,and a pseudocoelom 
D) An exoskeleton,Malpighian tubules,and a pseudocoelom 
E) Metanephridia,a true coelom,and open circulation 
A) Segmentation,open circulation,and metanephridia 
B) Segmentation,a closed circulatory system,and metanephridia 
C) An exoskeleton,metanephridia,and a pseudocoelom 
D) An exoskeleton,Malpighian tubules,and a pseudocoelom 
E) Metanephridia,a true coelom,and open circulation

Exam 17: Annelids and Allied Taxa

Of what evolutionary significance is the "hydrostatic skeleton"?

When earthworms mate,the _______________ secretes mucus to hold them together.

The circulatory system in the earthworm

The remaining valid use of "medicinal leeches" is to

Why does the wound from the bite of a leech bleed profusely?

A unique feature of the leech nervous system is that

Discuss why segmentation is such an important innovation in the Annelida.

In leeches,a cocoon into which fertilized eggs will be deposited is secreted by the __________.

The body wall of an annelid consists of

Each internal compartment of an annelid is lined with

Paired appendages used for locomotion in polychaetes are called ___________________.

The spaces in the coelom of leeches are called the _______________.

A leech

Why do zoologists not have a well-accepted theory for the origin of segmentation?

The circulatory system of earthworms is

In the earthworm,the typhlosole

A biologically plausible reason that burrowing earthworms have solid segmental walls but nonburrowing and parasitic annelids often have partial septa is

In the earthworm,food is drawn into the mouth by the pumping action of the _____________.

Select the list of characteristics typical of annelids.

Life: Biological Principles and the Science of Zoology

The Origin and Chemistry of Life

Cells As Units of Life

Cellular Metabolism

Genetics: a Review

Organic Evolution

The Reproductive Process

Principles of Development

Architectual Pattern of an Animal

Taxonomy and Phylogeny of Animals

Unicellular Eukaryotes

Sponges and Placozoans

Cnidarians and Ctenophores

Acoelomorpha, Platyzoa, and Mesozoa

Polyzoa and Kryptrochozoa

Molluscs

Smaller Ecdysozoans

Trilobites, Chelicerates, and Myriapods

Crustaceans

Hexapods

Chaetognaths, echinoderms, and Hemichordates

Chordates

Fishes

Early Tetrapods and Modern Amphibians

Amniote Origins and Nonavian Reptiles

Birds

Mammals

Support, Protection, and Movement

Homeostasis: Osmotic Regulation, Excretion, and Temperature Regulation

Homeostasis: Internal Fluids and Respiration

Digestion and Nutrition

Nervous Coordination: Nervous System and Sense Organs

Chemical Coordination: Endocrine System

Immunity

Animal Behavior

Animal Distribution

Animal Ecology

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