TF阅读真题第796篇Hermit Crabs in Snail Shells

Hermit Crabs in Snail Shells

Hermit crabs depend on a properly fitting snail shell for protection from predators. Crabs in shells that are too small grow more slowly, are less tolerant of air exposure and drying out, and are more likely to be eaten by a predator than those that can withdraw completely into their shell. When a crab has outgrown its snail shell, it has to look for a bigger one that fits properly. They locate shells by smell, either when the preceding owner (the snail) dies and begins to decay or by detecting calcium, the major component of snail shells. The crabs do not generally kill snails to find new shells, although they may fight with other hermit crabs over empty shells, especially when empty shells are scarce. After locating a new shell, the crab investigates its surface and internal size by rolling it over and exploring it with its claws and walking legs. If it looks like a good fit, the crab withdraws its abdomen from its old shell and inserts it into the new one so quickly that it can be difficult to see. Switching shells is risky-the crab could be attacked by a predator or lose one or both shells to other hermit crabs.  

Crabs rarely abandon their current shells without a new home lined up. However, if a crab has been buried in the sand during a storm or flooding event, it is likely to abandon its shell to return to the surface. Although abandoning its shell increases its chances of surviving such a burial, this behavior also increases the risk of predation and of being buried or injured in another flooding event.  

Particular species of hermits tend to prefer certain species of snail shells, but size is the critical factor. Occupying larger and heavier shells gives them greater protection, but it takes more energy to lug a large house around. Shells often become covered with other organisms, such as barnacles or algae, that make them heavier and more difficult to carry. Some hermit species live in shells that get entirely covered by bryozoan colonies that eventually dissolve the snail shell, leaving the crab with a house composed entirely of the bryozoans. As the bryozoan colony grows, so too do the crabs, so these crabs have no need to change their homes.  

Hermit crabs with poor-fitting shells are chemically attracted to dying gastropods (snails and related animals) and other hermit crabs, where a shell may become available. In the Mediterranean species Clibanarius erythropus, gastropod predation sites attract dozens of hermit crabs. Researcher Elena Tricarico and colleagues observed that these aggregations function as shell exchange markets: the first crab to arrive takes the empty shell, and a chain of shell exchanges among the crabs follows. They found that simulated snail predation sites quickly attracted a larger number of hermit crabs than other types of sites; therefore, aggregation is the most efficient tactic for this species to acquire new shells. In Belize, the land hermit Coenobita clypeatus has an even more organized shell exchange in what is called a “synchronous vacancy chain” by Randi Rotjan and colleagues, who discovered this unique behavior. When a large, empty shell becomes available, many crabs gather around it, which can take hours. As they gather, the crabs arrange themselves into a line of decreasing size, starting with the largest crab holding onto the empty shell. As though choreographed, the crabs begin shell swapping, one after the other, a smaller crab climbing into a new shell right after it is vacated by the slightly larger crab ahead of it. What makes the synchronous chain possible is that smaller crabs linger near a too-large shell, perhaps attracting others, waiting until a bigger crab comes along, which increases their chances of getting a good-fitting hand-me-down.  

Most hermit crabs and most snails are right-handed and spiral clockwise. Some species, however, are left-handed and spiral counterclockwise, and they need to find snail shells that are coiled that way. Since the majority of snail species are right-handed, left-handed hermits may have trouble finding left-handed snails. Adults of the left- handed Petrochirus diogenes, the largest hermit crab in the Caribbean, are often found in shells of the queen conch Eustrombus gigas. As an exception to the general rule, they will attack and eat the conch, thus obtaining both a meal and a shell.

 

 

 

 

1

Hermit crabs depend on a properly fitting snail shell for protection from predators. Crabs in shells that are too small grow more slowly, are less tolerant of air exposure and drying out, and are more likely to be eaten by a predator than those that can withdraw completely into their shell. When a crab has outgrown its snail shell, it has to look for a bigger one that fits properly. They locate shells by smell, either when the preceding owner (the snail) dies and begins to decay or by detecting calcium, the major component of snail shells. The crabs do not generally kill snails to find new shells, although they may fight with other hermit crabs over empty shells, especially when empty shells are scarce. After locating a new shell, the crab investigates its surface and internal size by rolling it over and exploring it with its claws and walking legs. If it looks like a good fit, the crab withdraws its abdomen from its old shell and inserts it into the new one so quickly that it can be difficult to see. Switching shells is risky-the crab could be attacked by a predator or lose one or both shells to other hermit crabs.  

The word “preceding” in the passage is closest in meaning to

Asick

Bearlier

Csimilarly sized

Dnatural

 

2

Hermit crabs depend on a properly fitting snail shell for protection from predators. Crabs in shells that are too small grow more slowly, are less tolerant of air exposure and drying out, and are more likely to be eaten by a predator than those that can withdraw completely into their shell. When a crab has outgrown its snail shell, it has to look for a bigger one that fits properly. They locate shells by smell, either when the preceding owner (the snail) dies and begins to decay or by detecting calcium, the major component of snail shells. The crabs do not generally kill snails to find new shells, although they may fight with other hermit crabs over empty shells, especially when empty shells are scarce. After locating a new shell, the crab investigates its surface and internal size by rolling it over and exploring it with its claws and walking legs. If it looks like a good fit, the crab withdraws its abdomen from its old shell and inserts it into the new one so quickly that it can be difficult to see. Switching shells is risky-the crab could be attacked by a predator or lose one or both shells to other hermit crabs.  

Why does the author point out that “Switching shells is risky” for hermit crabs?

ATo suggest that hermit crabs rarely switch shells

BTo illustrate the consequences of moving into a poorly fitting shell

CTo provide an explanation for why many hermit crabs remain in a shell that is too small for them

DTo explain why hermit crabs insert themselves into their new shell very quickly

 

3

Hermit crabs depend on a properly fitting snail shell for protection from predators. Crabs in shells that are too small grow more slowly, are less tolerant of air exposure and drying out, and are more likely to be eaten by a predator than those that can withdraw completely into their shell. When a crab has outgrown its snail shell, it has to look for a bigger one that fits properly. They locate shells by smell, either when the preceding owner (the snail) dies and begins to decay or by detecting calcium, the major component of snail shells. The crabs do not generally kill snails to find new shells, although they may fight with other hermit crabs over empty shells, especially when empty shells are scarce. After locating a new shell, the crab investigates its surface and internal size by rolling it over and exploring it with its claws and walking legs. If it looks like a good fit, the crab withdraws its abdomen from its old shell and inserts it into the new one so quickly that it can be difficult to see. Switching shells is risky-the crab could be attacked by a predator or lose one or both shells to other hermit crabs.  

According to paragraph 1, all of the following are disadvantages a hermit crab may experience when occupying a shell that is too small EXCEРT:

AThe crab is more likely to suffer from drying out.

BPredators can reach the crab more easily.

CThe crab has less access to fresh air.

DThe crab grows more slowly.

 

4

Hermit crabs depend on a properly fitting snail shell for protection from predators. Crabs in shells that are too small grow more slowly, are less tolerant of air exposure and drying out, and are more likely to be eaten by a predator than those that can withdraw completely into their shell. When a crab has outgrown its snail shell, it has to look for a bigger one that fits properly. They locate shells by smell, either when the preceding owner (the snail) dies and begins to decay or by detecting calcium, the major component of snail shells. The crabs do not generally kill snails to find new shells, although they may fight with other hermit crabs over empty shells, especially when empty shells are scarce. After locating a new shell, the crab investigates its surface and internal size by rolling it over and exploring it with its claws and walking legs. If it looks like a good fit, the crab withdraws its abdomen from its old shell and inserts it into the new one so quickly that it can be difficult to see. Switching shells is risky-the crab could be attacked by a predator or lose one or both shells to other hermit crabs.  

According to paragraph 1, what is the first thing a hermit crab does after locating a new shell?

AForce the current owner out of the shell

BInsert its abdomen into the shell quickly

CDetermine whether the shell is the right size

DRoll over to make switching shells easier

 

5

Particular species of hermits tend to prefer certain species of snail shells, but size is the critical factor. Occupying larger and heavier shells gives them greater protection, but it takes more energy to lug a large house around. Shells often become covered with other organisms, such as barnacles or algae, that make them heavier and more difficult to carry. Some hermit species live in shells that get entirely covered by bryozoan colonies that eventually dissolve the snail shell, leaving the crab with a house composed entirely of the bryozoans. As the bryozoan colony grows, so too do the crabs, so these crabs have no need to change their homes.  

Paragraph 3 discusses which TWO of the following as possible effects of organisms that may cover a hermit crab’s shell? To receive credit, you must select TWO answers.

AOrganisms on the shell force the crab to spend more energy in carrying the shell around.

BOrganisms that dissolve the shell leave the crab at risk from predators.

COrganisms can form colonies that replace the shell.

DOrganisms on the shell allow the crab to obtain food without leaving its home.

 

6

Hermit crabs with poor-fitting shells are chemically attracted to dying gastropods (snails and related animals) and other hermit crabs, where a shell may become available. In the Mediterranean species Clibanarius erythropus, gastropod predation sites attract dozens of hermit crabs. Researcher Elena Tricarico and colleagues observed that these aggregations function as shell exchange markets: the first crab to arrive takes the empty shell, and a chain of shell exchanges among the crabs follows. They found that simulated snail predation sites quickly attracted a larger number of hermit crabs than other types of sites; therefore, aggregation is the most efficient tactic for this species to acquire new shells. In Belize, the land hermit Coenobita clypeatus has an even more organized shell exchange in what is called a “synchronous vacancy chain” by Randi Rotjan and colleagues, who discovered this unique behavior. When a large, empty shell becomes available, many crabs gather around it, which can take hours. As they gather, the crabs arrange themselves into a line of decreasing size, starting with the largest crab holding onto the empty shell. As though choreographed, the crabs begin shell swapping, one after the other, a smaller crab climbing into a new shell right after it is vacated by the slightly larger crab ahead of it. What makes the synchronous chain possible is that smaller crabs linger near a too-large shell, perhaps attracting others, waiting until a bigger crab comes along, which increases their chances of getting a good-fitting hand-me-down.  

The word “tactic” in the passage is closest in meaning to

Astrategy

Btype of cooperation

Cmovement

Daction

 

7

Hermit crabs with poor-fitting shells are chemically attracted to dying gastropods (snails and related animals) and other hermit crabs, where a shell may become available. In the Mediterranean species Clibanarius erythropus, gastropod predation sites attract dozens of hermit crabs. Researcher Elena Tricarico and colleagues observed that these aggregations function as shell exchange markets: the first crab to arrive takes the empty shell, and a chain of shell exchanges among the crabs follows. They found that simulated snail predation sites quickly attracted a larger number of hermit crabs than other types of sites; therefore, aggregation is the most efficient tactic for this species to acquire new shells. In Belize, the land hermit Coenobita clypeatus has an even more organized shell exchange in what is called a “synchronous vacancy chain” by Randi Rotjan and colleagues, who discovered this unique behavior. When a large, empty shell becomes available, many crabs gather around it, which can take hours. As they gather, the crabs arrange themselves into a line of decreasing size, starting with the largest crab holding onto the empty shell. As though choreographed, the crabs begin shell swapping, one after the other, a smaller crab climbing into a new shell right after it is vacated by the slightly larger crab ahead of it. What makes the synchronous chain possible is that smaller crabs linger near a too-large shell, perhaps attracting others, waiting until a bigger crab comes along, which increases their chances of getting a good-fitting hand-me-down.  

According to paragraph 4, which of the following is true of the shell exchanges of the Mediterranean hermit crab species Clibanarius erythropus?

AThey are not as organized as the synchronous vacancy chains of Coenobita clypeatus are.

BThey are not as competitive as the shell exchanges of Coenobita clypeatus are.

CThey begin after the crabs arrange themselves into a line of decreasing size.

DThey are more advantageous to larger crabs than to smaller ones.

 

8

Most hermit crabs and most snails are right-handed and spiral clockwise. Some species, however, are left-handed and spiral counterclockwise, and they need to find snail shells that are coiled that way. Since the majority of snail species are right-handed, left-handed hermits may have trouble finding left-handed snails. Adults of the left- handed Petrochirus diogenes, the largest hermit crab in the Caribbean, are often found in shells of the queen conch Eustrombus gigas. As an exception to the general rule, they will attack and eat the conch, thus obtaining both a meal and a shell.

Which of the following can be inferred about “Eustrombus gigas”?

AThey often attack and eat hermit crabs.

BThey sometimes have trouble finding a suitable shell to use as a home.

CTheir shells are too small for large adult Petrochirus diogenes to live in.

DThe species includes individuals whose shells coil in a counterclockwise direction.

 

9

Particular species of hermits tend to prefer certain species of snail shells, but size is the critical factor. Occupying larger and heavier shells gives them greater protection, but it takes more energy to lug a large house around. [■]Shells often become covered with other organisms, such as barnacles or algae, that make them heavier and more difficult to carry.[■] Some hermit species live in shells that get entirely covered by bryozoan colonies that eventually dissolve the snail shell, leaving the crab with a house composed entirely of the bryozoans. [■]As the bryozoan colony grows, so too do the crabs, so these crabs have no need to change their homes.  [■]

Look at the four squaresthat indicate where the following sentence could be added to the passage

 

However, one type of organism can benefit crabs when it covers their shells.

Where would the sentence best fit？Click on a square  sentence to the passage.

 

10

Hermit crabs use found snail shells as homes.

AAs a hermit crab grows, it typically needs to find a new shell that fits it in size and spirals in the same direction as its body.

BHermit crabs may fight each other for empty shells, but, apart from adult crabs of one species that eat their shells’ original occupants, they do not normally kill gastropods to obtain shells.

CSeveral hermit crab species use synchronous vacancy chains to compete with other crab species for shells at gastropod predation sites.

DOrganisms that cover and dissolve the shell are dangerous to hermit crabs. but bryozoan colonies are beneficial because they provide the crab with a source of food.

EHermit crabs are attracted to available shells by smell, and extensive shell exchanges occur after a large crab vacates its earlier shell to move into a bigger one.

FCertain hermit crab species do not use snail shells at all, which puts them at greater risk of predation but makes it easier for them to survive during storms and floods.