Some species of Saltwater Aquarium Invertebrates helping to maintain the plants. Moreover, they feeding on detritus too. These animals present a huge biological and ecological diversity, and this is one reason why they are so attractive to aquarists. Most invertebrates are very demanding as regards water quality.
The invertebrates have no backbone. Their body is soft, but it is protected on the outside, by a carapace in the case of the crustaceans, or by a shell in mollusks, or it is supported by an internal calcareous skeleton, as in corals. They adapt in surprising ways to ensure their survival. The crustaceans, for example, can walk or swim to look for food or flee an enemy, while corals and anemones unfurl to capture micro particles, such as plankton, in open water, or retract to escape their predators.
The Coelenterates slightly more evolved than sponges, were also classed as vegetables for many years; even now the term animal-flowers is used to describe them. The Coelenterates comprise medusas ("jellyfish") -but, they rarely seen in aquariums.
Worms are barely evolved soft-bodied animals. They are more common in aquariums as live food than as residents. A few specific species can be kept in captivity in sea water. They live in a tube and are often sedentary. The coloring of worms can vary enormously, but they are usually blue or purple, flecked with white, and almost always bicolor.
Mollusks body is protected by a shell, which has two parts- these are the bivalves - or a single part - as in the case of the gastropods. The bivalves half-open their shell - formed, as their name suggests, by two valves - to filter water. In this way they absorb oxygen and capture food particles, particularly vegetal plankton. Keeping them in an aquarium does not, therefore, pose any problems.
The crustaceans' bodies are protected by an articulated carapace. The animal abandons its carapace when it becomes too small due to body growth; this phenomenon is called the molt. The crustacean is particularly vulnerable to attacks from predators during the formation of the new carapace.
The two pairs of antennae, highly developed in shrimps, play a tactile and sensory role. Crustaceans are carnivorous, and can feed on live or dead prey - they are not difficult to feed in an aquarium.
These possess a symmetry based on five, which is extremely rare in nature, as most animals have a binary symmetry, meaning that, if they are cut down the middle, two identical parts can be observed. This is not possible with echinoderms, because they have to be cut into five sections to obtain identical pieces. Echinoderm means spiny skin: this is highly appropriate in the case of sea urchins, less so in relation to the rough starfish. Generally speaking, echinoderms will not survive for long outside water.