Invertebrates Crustaceans

It is easy to keep a few species of Crustaceans in a saltwater aquarium, to take advantage of their bright colors. These invertebrates are carnivorous: in an aquarium they should be fed on mussels, fish, or white meat. The most common species in marine aquariums are shrimps - usually brightly colored, although more subdued species are also found - and they are imported on a fairly regular basis. These animals pick up food left over by fish and in this way they contribute to the equilibrium of the aquarium.

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Shrimps play an ecological role by feeding on fishes' leftovers.

• Shrimps
These rarely swim and prefer to get about by walking on the decor. If they are disturbed they abruptly recoil by tucking up their abdomen. Several specimens can live together, but it is vital to keep them away from carnivorous fish.

These very brightly colored animals are much appreciated by hobbyists for the theatrical flourish they add to a tank. They are relatively easy to keep if the water quality is good and the aquarium is equipped with hiding places. New species regularly crop up on the market.

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- Stenopus Hispidus
This is one the most common shrimps in the aquarium trade. In their natural habitat (several tropical seas), the barber shrimps live in couples and serve as cleaners, especially for angelfish (Pomacanthids). They abandon this role, totally or partially, in an aquarium if they are well fed. Like many shrimps, they pick up the food rejected or ignored by fish. The male searches for food and gives it to the female.

It is best to keep a couple in a tank and provide them with hiding places, where they will take refuge by day, as they are most active in the dark. In good conditions, this shrimp molts several times in a year, particularly if it is well fed. Size: 7-8 cm.

- Lysmata Amboinensis (formerly L. grabhami)
This very sociable cleaner shrimp tolerates the presence of other shrimps and can also live in groups. It cleans the skin of certain fish with its antennae, which also detect the presence of the specimen to be "cleaned." Apart from the usual food, you can also try providing filamentous algae for this shrimp, as it searches for microorganisms in them. Size: 7-8 cm.

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- Lysmata Debelius
This is a timid species that lives in couples and prefers temperate waters to tropical ones. The red shrimp is still rarely found on the market, like other species of the same genus, such as Lysmata wurdemanni. The latter resembles the L. seticaudata, which is native to the Mediterranean and also to tropical regions, and is very popular in Europe. Size: 7-8 cm.

• Crabs

The small abdomen is tucked under the lower part of the body. Their pincers are particularly well developed. The larger specimens, which can be aggressive, must not be put into marine aquariums, as they can attack other invertebrates, and sometimes even fish.

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Neopetrolisthes sp. cannot live without an anemone,
such as one from the Stichodactyla genus.

Some small species can occasionally be found in the aquarium trade. In captivity, it is best to keep a single specimen, which can be fed on nauplii of brine shrimps or very fine slithers of mussels. Species of the Neopetrolisthes genus (porcelain crabs) live in symbiosis with anemones (for example, Stichodactyla gigantea) and feed on small particles using a pair of claws equipped with tiny fringes. Size: 4-5 cm.

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Enomotoplus sp., the lobster crab, related to the
langoustine, is an attractive and placid resident.

• Pagurids (Hermit Crabs)
These are better known as hermit crabs. Some tropical species can be found commercially, some of them bearing a small anemone on the gastropod shell which houses them. The shell is discarded when it becomes too small for the growing animal, so it is vital to provide bigger ones, as, unlike other crustaceans, a pagurid's abdomen is not protected by a carapace that it makes itself.

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Hermit crabs are highly striking invertebrates which run around the aquarium in all directions to look for their food. They withdraw into their shell when frightened.

These are sometimes considered the garbage collectors of the aquarium as they eat a wide range of detritus. It is not advisable to introduce them into a tank with other invertebrates (except, perhaps, the smaller species), although there is little risk in an aquarium inhabited by fish, as they can withdraw into their shell. The names of the species found on the market are often not known. Size: 4-6 cm.

• Other Crustaceans
- Odontodactylus Scyllarus
The aggressive mantis shrimp spends much of its time prowling and swimming in search of food, but, even though it can bury itself in sand, it also needs a hiding place. In the light of its behavior and feeding habits (small crustaceans and fish), the mantis shrimp must not be kept in an invertebrate aquarium. Its size and agility make it suitable for cohabitation with certain fish. Size: 10-15 cm.

- Enoplometopus Occidentalis
Contrary to what may be inferred from its common name of lobster crab, this decapod, closely related to the langoustine, is not aggressive. By day it remains hidden in a shelter, coming out at night to feed on the bed of the aquarium (leftover fish food, especially mussels, and sometimes filamentous algae). This is a crustacean worthy of a place in an invertebrate tank. Size: 10-15 cm.