Caprellids

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Onglets

Description

Distinguishing features

There are many species of caprellids, and it is difficult to differentiate one from the other. They are all small marine crustaceans with a shell like crabs, and resembling tiny skeleton shrimps or even small praying mantises.

The head has 2 pairs of antennae, one of which has bristles used to push food towards the mouth.

The elongated and cylindrical body has 8 legs (4 at each end) fitted with hooks, which allow the animal to cling to the substrate.

The gills are found in the middle of the body, on the ventral part. If the belly is swollen, it is a female carrying eggs inside her.

There is sexual dimorphism in caprellids, with males being larger than females. Caprellids move like inchworms: they advance the front part of the body, then the rear part joins the front one, and so on.

Reproduction

Generally, the male grabs the female with his hind legs, although in some species the front legs are used.

Breeding is possible throughout the year, but the chances of success are better in the spring.

A female can reproduce several times during her year of life. She carries 16 to 21 eggs, whose diameters vary between 0.25 and 0.30 mm.

There is no larval stage. The fertilized egg develops in the female’s ventral pouch and when mature, a small caprel is released. Generally, these young caprellids immediately disperse into the environment.

The fact that there are no larval stages ensures a better survival rate for the caprellids.

Diet

Caprellids mainly eat detritus (86% of their diet). Some species, on the other hand, are obligate predators and will consume small crustaceans and polychaete worms.

Prey is captured using the hooks on their front legs, which act as pincers. The presence of many serrated hairs on the opposite side of the hook makes it easier to hold on to their food.

Predators

Caprellids are the prey of many fish living around macroalgae. Some nemertean worms (ribbed worms) such as Tetrastemma elegans also attack caprellids. By remaining motionless, a caprellid can go unnoticed by fish.

Some years, when the environmental conditions are right, there are caprellid population explosions, to the delight of all their predators.

Habitat

Caprellids are opportunistic. As soon as the seabed is disturbed, they quickly colonize the vacant space. They are common on all types of seabed algae. Their small size and the presence of hooks on their legs allow them to cling easily to the substrate even when currents are strong.

The presence of caprellids is an indicator of the health of an environment. They attach themselves to macroalgae, but are also capable of clinging to dock beams, fishing nets, buoys, floating plastics and the bodies of other animals such as starfish, crabs and sea urchins.

Caprellids are commensals, that is to say they benefit from a host species without harming it: for example, by living on it and feeding on debris, dead skin, or parasites found on the surface of its body.

Ecology, behaviour

Rapid growth, high reproduction rate, a flexible diet, high environmental tolerance – caprellids have everything they need to succeed.

Those who are commensals play a very important role in cleaning up and ridding their hosts’ bodies of possible invaders, reducing the risk of disease.

Some caprellids travel around the world in the ballast of ships. If the conditions are right, they can become true invaders and harm the health of a natural environment. Unfortunately, their impact on the environment is still poorly understood.

French name

Caprelles

Scientific name

Caprella sp

Phylum

Arthropoda

Class

Crustacea

Order

Amphipodes

Family

Caprellidae

Size

Length : from 1 mm to 2 cm

Weight

10 to 25 mg (approximative)

Life span

About 1 year

Status

Non-threatened species Not evaluated by IUCN

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