The Horseshoe Crab's Ancient Design
Written by Studio AM.
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A horseshoe crab pushes across a tidal flat beneath a domed shell. Despite its name, it is more closely related to spiders and scorpions than to true crabs. Its lineage reaches far back in the fossil record, and its general body plan has remained recognizable through immense environmental change.
That history often earns the animal the label “living fossil.” The phrase can be misleading. Modern horseshoe crabs are not unchanged specimens from an ancient sea. Their populations have continued evolving, and the environments around them have changed. Some body features can remain useful while other traits continue to change.
Along parts of the Atlantic coast, adults gather on beaches around high tides to lay and fertilize eggs in sand. Many eggs remain buried, while some near the surface become food for migrating shorebirds. The cycle connects offshore animals, narrow spawning beaches, and birds traveling across continents. The shell protects the body, jointed legs move and handle food, and book gills exchange gases in water. A tail spine helps the animal right itself if waves overturn it; it is not a stinger. Each familiar feature belongs to a living animal meeting present conditions.
Shore alteration, harvesting, and changing water conditions can disrupt different parts of the cycle. Protecting horseshoe crabs therefore involves more than admiring ancient ancestry. It requires attention to spawning habitat, connected food webs, and the timing of human activity. The durable design survived past changes, but that history does not guarantee safe passage through every new one.
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Questions
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Question 1 of 4
What is the main idea of the passage?
The answer is C: Horseshoe crabs have an ancient, durable body plan, but they remain evolving animals dependent on vulnerable modern habitats and relationships.
The passage corrects the living-fossil idea while connecting form, life cycle, ecology, and present risk.
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Question 2 of 4
Why does the author call “living fossil” potentially misleading?
The answer is D: It can imply that modern animals stopped evolving and live outside changing environments.
The second paragraph rejects the image of an unchanged ancient specimen while allowing continuity of form.
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Question 3 of 4
What does “lineage” mean in the opening paragraph?
The answer is A: a continuing ancestral line through generations
The fossil record traces the ancestral group across a very long span of time.
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Question 4 of 4
What does the tail spine help a horseshoe crab do?
The answer is B: turn itself upright after being overturned
The third paragraph explains the righting function and directly denies that the spine is a stinger.
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