Prawns & Shrimps

Both shrimps and prawns are decapods, the term meaning 10 legged. Those most commonly found, are the Common Shrimp Crangon crangon and the Common Prawn Palaemon serratus. Both of these creatures are often confused with each other. This is understandable as the division between shrimps and prawns is not scientific but only a layman’s grouping.

Ecdysis 

As with other creatures that have an exoskeleton, they have to shed this inflexible outer coating of armour before they can grow. After shedding the body has a chance to expand before the new exoskeleton hardens. This process of shedding the exoskeleton and a new one hardening is called ecdysis. As the exoskeleton is there to protect, it is ineffective until it hardens. Fortunately the process of shedding the old takes under a minute and reaches full strength in a couple of days. Young prawns and shrimps grow fast during the summer months and moult up to four times a month.

Movement

Toward the rear of the body there are five pairs of swimmerets, these are used to swim forward. However if aggravated a faster motion is obtained, by flexing the abdomen which flicks the tail, propelling the animal backwards.

Reproduction

Mating can only occur after the female has shed her exoskeleton and while her skin is still soft. The female carries the fertilised eggs (which number in the thousands) under her body between the swimmerets. This not only protects the eggs but the pulsing swimmerets, keeps them aerated. After hatching the larvae are carried by the currents and join other plankton.

Distinguishing Between the Common Prawn & Common Shrimp

Both creatures are closely related and hence share similar features. As decapods both have five pairs of legs. The prawn walks on the rear three pairs, the front two pairs are used for eating and have pincers, the largest being on the second pair. The shrimp’s two front pairs are also pincered, but in this case it is the front pair that are the largest, and considerably so. The prawn’s legs are longer than those of the shrimp’s.

Both shrimps and prawns have their eyes on the end of stalks. Both creatures have two pairs of antenna used to detect their food, one pair is much longer than the other.

With the prawn the head is extended in front to form a spike the rostrum, which has several toothed like projections on top of it.

The prawn is semi transparent its internal organs can easily be seen, the shrimp has more pigment typically sandy coloured.

The common prawn is more of a rocky shore animal, while the prawn is more of a sandy shore creature.

Common Prawn Palaemon serratus

Common prawns are semi transparent creatures, their internal organs visible through the skin. They are found on rocky beaches.

The common prawn can reach four inches in length, but those seen in rock pools never reach anywhere near this length.

Even with being transparent they are still relatively easily seen, particularly when they are disturbed as their jerky backwards darting motion makes them conspicuous in a calm rock pool.

The first two pairs of legs have pincers the second pair being the larger. These are used for feeding on seaweed and carrion.

Common Shrimp Crangon crangon

The common shrimp’s body has more colour to match its background sand, this is made more effective as the colour pigments can be modified. They are an important commercial species.

The shrimp is a nocturnal bottom feeder, hunting at night using its antenna to detect its food. During the day they bury in the sand with only their antennae exposed. They may be very common on a beach, but are only seen when disturbed and this will be just a quick darting movement highlighted by a small disturbance in the sand.

The first two pairs of legs have pincers with the front pair pincers being enlarged. Just like the common prawn, the common shrimp is an opportunist feeder, consuming seaweed, carrion but with its larger pincers also smaller animals. The common shrimp can reach up to two inches in length.