Sharp Front Legs

Crustaceans have appendages that generally branch in two directions and are adapted to aquatic life. A characteristic shared by all crustaceans is their articulated shell, which leaves two pairs of antennae uncovered. They also have a pair of mandibles, two pairs of maxillae, and a pair of appendages in each segment of the body. Their pincers have enough strength so they can trap their prey and feed themselves. The class Malacostraca includes lobsters, crabs, shrimp, and prawns, among other animals. •

DUBLIN BAY PRAWN

Nephrops norvegicus

ANTENNAE

The brain receives the information sent by the antennae and communicates with the rest of the body through the ventral nerve.

UROPODS

are shaped like a spade. The telson is like a barb. Both are used by the shrimp for its characteristic escape backwards.

PLEOPODS

First five pairs of abdominal appendages

PINCERS

are mobile appendages that it uses for defense and attack. With its pincers, the shrimp can trap its prey with a great deal of pressure so that it cannot escape.

PEREIOPODS

Five pairs of appendages

TELSON

Fin-like structures used for swimming. The telson makes up the caudal fan together with the last abdominal segment and the uropods. There are no appendages.

FRONT VIEW

Shrimp is the name for about 2,000 species of crustaceans of the suborder Natantia. Shrimp are characterized by their semitransparent and flat bodies, with appendages modified for swimming, and by their long antennae. Their length varies between 0.1 inch and about 8 inches (from a few mm to 20 cm), depending on the species. They live in salt water, brackish water, and fresh water. They survive by burying themselves for almost the entire day and coming out at dusk to catch their food.

DUBLIN BAY PRAWN

Nephrops norvegicus

ANTENNAE

The brain receives the information sent by the antennae and communicates with the rest of the body through the ventral nerve.

UROPODS

are shaped like a spade. The telson is like a barb. Both are used by the shrimp for its characteristic escape backwards.

PLEOPODS

First five pairs of abdominal appendages

FIRST TWO PAIRS

have been adapted for sexual functions.

LAST THREE PAIRS

are similar to each other and are used to swim.

FRONT VIEW

PINCERS

are mobile appendages that it uses for defense and attack. With its pincers, the shrimp can trap its prey with a great deal of pressure so that it cannot escape.

Lobster

A lobster is characterized by two enormous pincers formed by the first pair of legs. It lives on rocky bottoms in shallow water, and it migrates seasonally toward the coast in summer and to greater depths in winter. The lobster is typically a nocturnal animal seeking its food when the Sun sets. Its food consists mainly of mollusks, bivalves, worms, and fish.

TELSON

Fin-like structures used for swimming. The telson makes up the caudal fan together with the last abdominal segment and the uropods. There are no appendages.

55,000

LIVING SPECIES AND AS MANY FOSSIL SPECIES ARE PART OF THIS GROUP OF INVERTEBRATES.

PEREIOPODS

Five pairs of appendages

FIRST THREE PAIRS

are used to feed itself. The pincers catch and hold prey.

LAST TWO PAIRS work as walking legs that are aided by the pleopods.

AT REST

The body remains close to the ground, the center of gravity is lowered, and movements are slow and rhythmic.

PENDULUM

SLOW WALK

The body operates like the weight of a pendulum. Close to the ground, it saves energy by moving in a swinging motion.

Crab

Of all crustaceans, the crab has surprising mobility and agility. It has five pairs of legs, four of which are walking legs, despite the fact that it moves laterally instead of forward. The crab-like movement is due to the placement of its legs and the general design of its body. A crab's walk is funny, but its technique is effective for both swimming and walking, even over such varied surfaces as beach sand, rock, and -for some species- tree branches.

AT REST

The body remains close to the ground, the center of gravity is lowered, and movements are slow and rhythmic.

PENDULUM

SLOW WALK

The body operates like the weight of a pendulum. Close to the ground, it saves energy by moving in a swinging motion.

CUTTING CLAW CUTTING EDGE

Thinner and with sharp edges, it is used to cut the meat of its prey.

TEETH

The lobster has thick, strong teeth and a muscle capable of crushing snail shells, clams, and even a human finger.

LOBSTER

Homarus vulgaris

Resistance power

Joint

Muscle

The body, elevated higher than its joints, tends to fall like an inverted pendulum, which helps with movement.

LOBSTER

Homarus vulgaris

CUTTING CLAW CUTTING EDGE

Thinner and with sharp edges, it is used to cut the meat of its prey.

Resistance power

CRUSHING CLAW

TEETH

The lobster has thick, strong teeth and a muscle capable of crushing snail shells, clams, and even a human finger.

REBOUND EFFECT

FAST WALK

Suspended from its joints, the body jumps by means of them and on them and multiplies the energy of its movement.

The body, elevated higher than its joints, tends to fall like an inverted pendulum, which helps with movement.

WALKING-

LEGS

are situated in the céphalothorax, and even though they are rather small in relation to the body, they are capable of providing movement

JOINTS AND LEVERS

Crustaceans, with slim limbs and little space for large muscles, are able to move with great strength because the majority of their joints function as simple levers, with the lever arm corresponding to the limb itself, and the fulcrum corresponding to the joint.

Joint

Muscle

42 CRUSTACEANS AND ARACHNIDS

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