horseshoe crab

noun

: any of several closely related marine arthropods (family Limulidae and order Xiphosura) with a broad crescentic cephalothorax, six pairs of legs, and a spikelike tail

especially : one (Limulus polyphemus) of coastal waters from Maine to the Yucatán Peninsula

Note: The horseshoe crab is often said to have five pairs of legs since the first pair is greatly reduced in size and used mainly for feeding. All the legs of the horseshoe crab end in claws except for the last pair of legs which have leaflike expansions used mainly for pushing.

… a horseshoe crab … is a Swiss army knife of jointed limbs—for walking, swimming, grasping, shredding, and defending.

—Carl Zimmer

… the horseshoe crab has changed little since an ancestor was fossilized 150 million years ago …

—National Geographic

called also king crab

Examples of horseshoe crab in a Sentence

Recent Examples on the Web

In fact, the gills resemble the same structure that horseshoe crabs possess, which is called the opisthosoma. —Greta Cross, USA Today, 16 May 2025

The researchers compared its rear section to modern arthropods such as insects and horseshoe crabs. —Julia Jacobo, ABC News, 14 May 2025

The team even revealed that the same genetic mechanism builds the gills of horseshoe crabs, invertebrates that have changed very little over the last 400 million years. —Sarah Kuta, Smithsonian Magazine, 23 Jan. 2025

What were these strange fossils that looked like horseshoe crabs and were so deeply embedded in the rocks? —Caroline Winterer / Made By History, TIME, 14 Jan. 2025

Word History

First Known Use

1797, in the meaning defined above

Rhymes for horseshoe crab

• ab
• cab
• dab
• drab
• fab
• gab
• grab
• jab
• lab
• mab
• nab
• rab

Kids Definition

horseshoe crab

noun

: any of several closely related arthropods that have a broad crescent-shaped united head and thorax and a tail resembling a spike