How Many Legs Do Crustaceans Have?

Crustaceans such as crabs, lobsters, and shrimp are common delicacies with their crunchy shells and sweet meat. But have you ever wondered, with all those legs and claws, just how many legs do crustaceans have? Read on to uncover the details.

If you’re short on time, here’s a quick answer to your question: Crustaceans have 10 legs/appendages. These include 2 chelipeds (claws), 4 walking legs, and 4 swimming legs.

In this comprehensive guide, we will provide an overview of crustacean anatomy, look at the different types of crustacean legs and appendages, explore leg function and purpose, examine how many legs major crustacean groups possess, and summarize the key points in a quick reference table for how many legs different crustaceans have.

Crustacean Anatomy Overview

Exoskeleton

Crustaceans have a hard external skeleton called an exoskeleton. This protective outer layer provides structure and support for the animal’s body. The exoskeleton does not grow with the crustacean, so it must periodically molt (shed its old shell) and produce a new, larger one.

The exoskeleton is made up of calcium carbonate and provides protection from predators.

Cephalothorax

The cephalothorax is the body section of the crustacean that consists of the head and thorax fused together as one unit. This body part contains the brain, stomach, mouth, antennae, and eyes of the crustacean.

Under the carapace (hard upper shell) of the cephalothorax are attached five pairs of appendages used for gathering food – maxillipeds and pereiopods. This structure provides stability and also protects vital internal organs.

Abdomen

The abdomen is the posterior body section of the crustacean. It contains the heart, reproductive organs, and parts of the digestive system. The abdomen is made up of 6-7 segments and also has smaller appendages called pleopods and ended by the tail fan called the telson.

The abdomen provides balance and enables swimming through rapid movements of the tail fan propelling the crustacean backwards. The pleopods play a role in brooding eggs and swimming.

Appendages

Crustaceans have 19 pairs of appendages in total attached to their bodies. These include:

• 2 pairs of antennae – sensory functions
• 5 pairs of maxillipeds – feeding manipulation
• 10 pairs of pereiopods – locomotion and gathering food
• 1 pair of uropods – balance and forward propulsion
• 1 telson – aids in balance and steering

The legs and other appendages enable the crustacean to move, feed, balance, steer, and sense their environment. The number and types of appendages differ between crustacean subgroups.

Types of Crustacean Legs and Appendages

Chelipeds (Claws)

Crustaceans like lobsters, crabs, and crayfish have large, powerful front claws called chelipeds. These claws are used for catching prey, fighting, and defense. Chelipeds can have pincers with teeth for holding and crushing food.

Some chelipeds like the coconut crab’s can exert an amazing 3,300 Newtons of force, enabling them to crack open coconuts!

Walking Legs (Pereopods)

Behind the chelipeds are several pairs of walking legs called pereopods. These legs propel crustaceans along the seafloor or land. Crabs have five pairs while lobsters and crayfish each have four. The pereopods work like small oars, pushing the animal forward.

Some pereopods are also used for grooming, mating, brooding eggs, or capturing prey.

Swimming Legs (Pleopods)

Crustaceans have smaller appendages under their tail called pleopods or swimmerets. These feathery pleopods create water currents that enable swimming. Pleopods also function in respiration, circulating oxygenated water over the gills.

In females, pleopods hold clusters of eggs until they are ready to hatch. Male crustaceans use specialized pleopods to transfer sperm to the female during mating.

Other Appendages

In addition to legs, crustaceans have various sensory and mouthpart appendages. Antennae detect chemicals and touch. Compound eyes provide vision. Mouthparts like mandibles, maxillipeds, and maxillae manipulate and ingest food.

These specialized appendages enable crustaceans to sense their environment and consume a wide variety of prey.

Leg Function and Purpose

Chelipeds Help Capture and Tear Food

The foremost pair of legs in crustaceans like lobsters, crabs, and crayfish are called the chelipeds. These appendages serve as pincers or claws used for grasping, tearing, and shredding food (Britannica).

The chelipeds contain sharp edges and pointed tips ideal for spearing prey, ripping flesh, and crushing hard-shelled organisms like molluscs and other crustaceans (ScienceDirect). Their powerful muscles and mechanical leverage enable chelipeds to snip objects cleanly like scissors.

Walking Legs Enable Motion on Sea Floor

Behind the chelipeds are several pairs of walking legs that let crustaceans like crabs and lobsters move across the seafloor and within rocky crevices (AMNH). These legs are longer and more slender than the thick crushing chelipeds.

Rows of stiff bristles on the tips of walking legs provide traction for gripping surfaces while exploring the sediment. Species like coconut crabs even climb trees with their strong walking legs.

Swimming Legs Allow Speed and Mobility in Water Column

While crabs and lobsters walk along the bottom with their rear legs, shrimp and krill use swimming legs to dart quickly through the water column. Their paddle-like appendages generate thrust to jet forward and make rapid escapes from predators.

Many small crustaceans migrate long distances vertically using swimming legs (ScienceDirect). Krill in particular form huge swarms and support entire marine ecosystems with their sheer biomass.

Other Appendages Aid in Respiration, Reproduction, Balance

In addition to locomotive legs, crustaceans have specialized mouthparts for filtering food, feather-like gills for breathing, egg-carrying appendages, and tail fins for stability. Barnacles are attached crustaceans that use feathery cirri legs to gather microscopic food particles (AMNH).

While not expressly for movement, these other appendages allow crustaceans to thrive through suspension feeding, oxygen intake, reproduction, and remaining upright in currents.

How Many Legs Major Crustacean Groups Possess

Crabs Have 8 Legs Plus 2 Claws = 10 Appendages

Crabs are one of the most recognizable crustaceans, with their sideways walk and large front claws used for defense and food gathering. All crabs have 8 jointed walking legs, connected to the top section of their body known as the cephalothorax.

In addition to their 8 legs, crabs also have 2 front claws called chelipeds, for a total of 10 appendages.

The crab’s claws are very useful tools and considered an additional pair of legs in terms of function. The claws are used to tear apart food, dig in sand or mud, defend against predators, and grasp objects. Male crabs often use their claws to attract female crabs.

So while they may not technically be “legs”, the crab’s claws allow them to walk, balance, feed, fight, and mate.

Lobsters Have 8 Legs Plus 2 Claws = 10 Appendages

Much like their crustacean cousins the crabs, lobsters also have a total of 10 functional appendages. They use 8 jointed walking legs connected to their thorax to creep along the seafloor. Lobsters also have 2 large front claws called chelipeds that they employ to capture prey, scoop food toward their mouth, and intimidate potential attackers.

A lobster’s claws are its primary tools and weapons, used for self defense, hunting, fighting, and feeding. Their long, spiney antennae also aid in navigation, detecting smells, and sensing vibrations.

So while the claws might not be true legs in terms of biological classification, they serve a similar purpose by enabling the lobster to effectively maneuver throughout its marine environment.

Shrimp Have 5 Pairs of Swimmerets Plus Claws and Legs = 10 Appendages

Like crabs and lobsters, shrimp also possess 10 appendages for moving around and interacting with their surroundings. In addition to 2 pairs of front claws and 5 pairs of walking legs, shrimp have smaller, hair-like structures under their tails called “swimmerets”.

Swimmerets function sort of like little oars to propel the shrimp through the water column. The swimmerets create water currents with synchronized paddling motions, allowing shrimp to dart backwards very quickly when needed.

So while not technically counted as “legs”, a shrimp’s swimmerets enable mobility and are crucial for survival from predators.

Barnacles Have 6 Pairs of Cirri

Unlike free-moving shrimp, crabs and lobsters, adult barnacles are sessile – meaning they attach their back end to rocks, ships, whales etc. and do not travel far. Since they are cemented in one place, barnacles do not use traditional legs for walking around.

Instead, barnacles have feather-like appendages called “cirri” that catch food particles from the water. Inside their calcareous shells, barnacles have 6 pairs of cirri that continually sweep back and forth, trapping plankton and detritus to eat. Other cirri aid in reproduction.

So while they are not locomotive structures, a barnacle’s cirri allow it to thrive and breed in its fixed position cementing to various surfaces in the intertidal zone.

Summary Table of Crustacean Legs

Crustaceans are a large and diverse group of arthropods that include crabs, lobsters, crayfish, shrimp, krill, barnacles and many more. They can be found in marine and freshwater environments across the world.

One of the defining features of crustaceans are their number of legs, which can vary greatly between species.

Here is a summary table of the number of legs for some common crustacean groups:

As the table shows, 10 legs arranged in 5 symmetrical pairs is the most common number for crustaceans like crabs, lobsters, crayfish and shrimp. However, some crustaceans like copepods and barnacles have fewer legs, while amphipods, isopods and mysids have more.

The reason for the variation in legs is due to evolutionary adaptation to different environments and lifestyles. For example, barnacles are sessile and use their legs mainly for feeding, whereas amphipods and isopods roam the seafloor on their many legs.

In terms of function, the frontmost pairs of legs are generally specialized for sensing and feeding. The rear pairs are for locomotion – walking sideways, swimming, or jumping. Species like shrimp have muscular rear legs adapted for powerful swimming bursts.

Conclusion

We have explored that crustaceans have a often have a total of 10 appendages, including 2 chelipeds used as claws, 4 walking legs, and 4 swimming legs that aid mobility. While crustaceans display an incredible diversity of forms and functions, they united by this body plan of 10 arthropod legs adapted for aquatic life.

We detailed how chelipeds help crustaceans capture prey and how walking legs enable locomotion along the seafloor. The pleopods or swimmerets can propel shrimp swiftly backwards by paddling through the water column. Other unique adaptations like barnacle cirri allow filter feeding.

Crustaceans have adapted an effective body plan of 10 appendages to survive every niche from filter feeding to active predation. We hope this guide gave you a comprehensive overview of crustacean anatomy and helped explain how many legs different crustaceans have.