Invertebrates are animals without backbones. This is a very numerous group: about 90% of known animal species are invertebrates. This group includes the Sponges, Echinoderms, Segmented Worms, Leeches, Flatworms, Roundworms, Ectoprocts, Entoprocts, Brachiopods, Coelenterates, Molluscs and Arthropods.
The Sponges (Phylum Porifera) are the simplest types of multicellular invertebrates. There are freshwater sponges in addition to the more familiar marine species. Segmented worms are found in the sea, fresh water, and in the soil; for example, marine annelid worms and earthworms. Phylum Coelenterata includes creatures such as jellyfish, hydras, corals, and sea anemones.
Molluscs live on land, in the sea and in freshwater, and include slugs, snails, limpets, clams, oysters, octopuses and squid. One important Irish freshwater mollusc is the Nore Freshwater Pearl Mussel, Margaritifera durrovensis, an endangered species protected by Irish law under the Wildlife Act, and by European law under the Habitats Directive. The Nore Pearl Mussel was first discovered and named as a species new to science in 1928 and the only known population worldwide is found in the Nore River. Pearl mussels grow very slowly and can live to over 100 years of age. The status of this species is critically endangered as there has been no successful recruitment of young in the last 20 years. The decline of this sensitive mollusc is thought to be linked to depressed river bed and water quality in its habitat.
The Echinoderms (meaning 'prickly skin') are exclusively marine animals - the starfishes, sea urchins, sea lillies, brittle stars, and sea cucumbers. The Echinoderms are a very ancient and diverse group. Starfish, one of our most familiar seashore animals, crawl slowly on about 1,000 hydraulically controlled and well-developed tube feet. They are carnivores and can extrude their stomachs around their prey. They use their many tube feet to pry open the shells of clams and many species can slip folds of the everted stomach inside the clam opening to begin the digestive process.
Arthropods are the most numerous animal group. Arthropods have an external skeleton and paired, jointed limbs. Phylum Arthropoda includes Crustaceans, Insects and Spiders. Crustaceans include crabs, lobsters, shrimp, krill, barnacles and wood lice. The lobsters include the largest invertebrates. In Ireland, a freshwater lobster called the White-clawed Crayfish, Austropotamobius pallipes, is widespread in lowland lime-rich streams and lakes. Our population is internationally important because it remains free of the plague carried by American crayfish species, which is now found in the rest of Europe. The White-clawed Crayfish is protected under the Berne Convention and the Habitats Directive and under the Irish Wildlife Acts.
The Insects are a varied group which includes wasps, bees, ants, flies, beetles, bugs, earwigs, grasshoppers, dragonflies, damselflies, butterflies and moths. In 1981, the Irish damselfly, Coenagrion lunulatum, was first discovered. It is found in small colonies in sheltered mesotrophic lakes and moderate sized pools on cutover bogs in Fermanagh, Tyrone, Armagh and Monaghan.
The Marsh Fritillary, Euphydras aurinia, is the only Irish butterfly species protected under the EU Habitats Directive. Once widespread, this species declined severely during the 20th century due to loss of uncultivated grasslands; overgrazing on remaining habitat; and its requirement for extensive habitat area and wildlife corridors. It is now considered one of the most endangered species in Europe so the Irish population is of international importance.
Marsh Fritillary Euphydryas aurinia (Photo: Mike Brown)
Reynolds, J.D. (1998) Conservation management of the white-clawed crayfish, Austropotamobius pallipes. Part 1. [2,010KB] Moorkens, E. A. (2000) Conservation management of the freshwater pearl mussel Margaritifera margaritifera. Part 2: Water Quality Requirements. [1,955KB] Anonymous (2004) Margaritifera margaritifera: Stage 1 and Stage 2 survey guidelines. [504KB] Moorkens, E. & Killeen, I. (2005) A survey of the molluscan fauna of a mixed farm in South County Cork, 2004. [1,184KB] Regional Red List of Irish Bees 2006 [576KB]