Invertebrates Coelenterates Hexacorals

Hexacorals group covers the majority of the Coelenterates found in saltwater aquariums, particularly anemones and corals. Do not forget that most of them need strong light, as they contain Zooxanthellae, and that they can be fed on small morsels of animal origin. The aquarist must take care when handling some species, as their capacity to sting can be considerable. The great majority of these animals are imported from the Indian or Pacific Oceans, but they are only sporadically available in the aquarium trade.

Sea Anemones (Actinia)
These live on the substrate, attached by their single foot, which acts as a sucker, but they can move around and find the place that suits them best (sometimes the tank's front pane). Some rare species live in the sand and can retreat into it. They are fairly robust in an aquarium if in water that is well lit and aerated (some anemones have Zooxanthellae).

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Anthozoa sometimes provide a refuge for shrimps, protecting them from their predators.

A large living space must therefore be planned for them, as other Anthozoa do not appreciate their tentacles; moreover, they sometimes excrete filaments of mucus that can pollute the water. Only clownfish can accustom themselves to contact with their tentacles. Anemones eat small pieces of mussel, shrimp, fish, or a choppy made from these ingredients.

Sexual reproduction is a possibility, and some anemones are livebearers; asexual multiplication can take place via budding, which will go on to produce a young anemone. When buying anemones, make sure that they are puffed out and unfurled, as these are signs of good health.

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Heteractis Magnifica

• Heteractis (formerly Radianthus)
This has a large number of tentacles, which are quite long (up to 10 cm) and somewhat rigid. Species of this genus can achieve a diameter of several doze centimeters, and they are appreciated by several species of clownfish. Diameter: 30-40 cm.

• Stichodactyla (formerly Stoichactus)
In its natural habitat a species of the Stichodactyla reaches lengths of 1 m. The tentacles are arranged in dense ranks, particularly round the edge of the anemone. Diameter: 20-50 cm.

Stichodactyla Mertensii

Entacmaea quadricolor sheltering the clownfish Amphiphon bicinctus.

• Entacmaea
This genus was created a few years ago to cover some species from the old Radianthus genus (the remainder being included in the Heteractis genus).

• Aiptasia
The glass anemones are often introduced to an aquarium along with rocks or water. They are livebearers that can quickly colonize a tank, to the detriment of other Anthozoa. However, they do have advantages in an aquarium with butterfly fish (Chaetodontid family), as they constitute these fishes' staple diet. Diameter: 5-10 cm.

Aiptasia sp.

Cerianthus sp.

• Ceriantharia
These resemble anemones, although they can be distinguished by their non-retractable tentacles. Moreover, they are not attached by a single foot but live in a self-secreted tube, whose support requires a layer of not too rough sand, 15-20 cm thick.
Ceriantharia feed on finely ground mussels, fish, shrimps, or brine shrimps. Certain species can sometimes be found in the aquarium trade, although their name is often unknown or incorrect. Height: 20-30 cm.

Colonial Anemones (Zoantharia)
These are neither anemones, as they live in colonies, nor corals, as they have no calcareous skeleton. These animals colonize rocks, mollusks' shells, and sometimes sponges, corals, and Gorgonians. They can harbor Zooxanthellae, and therefore need the appropriate light level.

• Parazoanthus sp.
This colonial anemone consists of small polyps which can reach a height of up to 2 cm, with tentacles that do not exceed 5 mm in length. They must be placed 10 or 20 cm under the water surface in an aquarium to take maximum advantage of the light, due to the presence of Zooxanthellae. They must not be put close to stinging Anthozoa. Like many other animals in this group, their food consists of a fine choppy based on mussels. When buying this encrusting anemone, make sure that it is attached to a rock.

Parazoanthus sp.

Corallimorpharia
These invertebrates, which are not corals - they have no skeleton - are known as discus anemones. They live attached by a foot that is less powerful than that of the anemone. The diameter of the disc shaped polyp varies from one species to another. The presence of Zooxanthellae demands strong light. Asexual reproduction through budding is possible in captivity. Size: 10-30 cm.

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Actinodiscus sp.

• Actinodiscus
Several species from this genus are available on the market, and they are easy to keep. Their feeding, identical to that of the animals above, should take place on a weekly basis, as Zooxanthellae supply a part of the substances they need to live and they sometimes reject the food offered by the aquarist.

Scleratinaria
True corals or madreporites live in a calcareous skeleton, into they which they can withdraw. This skeleton means that they make the most significant contribution to the building of coral reefs in tropical seas. These are the most difficult invertebrates to keep in a saltwater aquarium, as they require well-aerated water of the highest quality, with no suspended particles - and therefore crystal clear – and an extremely low nitrate content.

As they are very sensitive to nitrates, it is essential to partially change the water on a regular basis, in small volumes. The tentacles, often drawn in by day, unfurl at night to capture food. This does not mean that corals like darkness; on the contrary, they must be provided with a great deal of light, on account of the presence of Zooxanthellae.

They are carnivorous, feeding on animal plankton in their natural habitat and a choppy based on mussels or fish in captivity, once a week. A supply of calcium carbonate is desirable for the growth of the skeleton. Take care when placing them in an aquarium, as they should not come into contact with other Anthozoa once their tentacles have unfurled.

Acropora sp.

• Acropora (Acroporidae)
They are rarely imported alive but their skeletons are often used as decor in domestic aquariums. In the wild, their growth is rapid (a few centimeters per year) and they can exceed 1 m in height. Height: 20-50 cm.

• Fungia (Fungids)
These solitary (and therefore non-colonial) corals generally live on the sediment and do not take part in the construction of reefs. The distinctive skeleton can be used as a decorative feature. Diameter: 20 cm.

A Fungia sp.

Goniopora sp.

• Goniopora (Poritidae) The species from this genus are imported on a fairly regular basis, and are some of the easiest to keep in an aquarium. They prefer moderately aerated water. Size: 20-30 cm.

• Favia, Platygira (Favidae)
These are easy to keep in captivity and accept small, live prey. The colored tentacles are drawn in by day. Size: 20 cm.

• Leptosammia (Dendrophylliidae)
One temperate species in this genus also tolerates tropical temperatures:
Leptosammia pruvoti.
Its yellow-orange color and small size make it good for decoration. It is preferable - in fact, essential - to put it into the aquarium already attached to a support. Size: 5 cm.

• Plerogyra (Caryophylliidae)
The species in this genus, known as bubble corals, are quite easy to keep in an aquarium. The daytime "bubbles" withdraw at night to give way to stinging tentacles 1-5 cm long. In the wild, the bubbles provide the coral with a certain degree of protection, as the tentacles are not attacked by fish (butterfly fish, for example).

The color of the bubbles varies depending on the presence of Zooxanthellae, and these mean that this coral requires strong lighting. It is best to feed it at night - when the tentacles are unfurled - with relatively large, live prey. It is also possible to accustom it to eating a fine choppy based on seafood between the bubbles by day. Avoid allowing the bubble coral to touch other invertebrates, on account of its capacity to sting. Size: 20-30 cm.