The terrestrial invertebrates of Galapagos are the largest group of organisms with the highest species diversity, they are present in all habitats and represent an estimated 51% of the total biodiversity. Their ecological role is essential: they act as pollinators, are part of the food chain, participate in nutrient recycling of organic material and thus contribute to soil formation.
Like other organisms, terrestrial invertebrates arrived in Galapagos by a variety of dispersal mechanisms: active flight, passive drift and transport following, in most cases, the main marine currents that arrive at the islands from Central America, and southern South America.
The invertebrate fauna of Galapagos has been called imbalanced. Because of the oceanic origin of the islands, their complete geographic isolation, their climatic conditions, and a great habitat variety, some groups are much better represented here than others. Native species that the Galapagos Islands share with the South American mainland were already pre-adapted to survive in the harsh environments of the islands, but many more species evolved and adapted to open, available ecological niches and are now unique for the archipelago – they are endemic species found nowhere else on earth. One of the best examples are the land snails in the genus Bulimulus. With more than 60 different species, they all evolved here and are not well adapted to many different microclimates and habitats. Some species are restricted to particular islands and are often only found in very specific habitats.
The exact number of terrestrial invertebrates in Galapagos is still unknown. Until 2001, a total of 2289 species had been reported in the literature, but numbers of new records and newly described species are still being added to that list. As much as 51.7% of these species are today reported to be endemic to Galapagos. The group with the highest species diversity are the insects, and in particular, the following taxonomic orders: Coleoptera, Diptera, Hemiptera, Hymenoptera y Lepidoptera. Other groups are less well represented: Diplura, Thysanura, Odonata, Mantodea, Embidina, Zoraptera, Stresiptera. Particularly poorly studied, but very species rich groups are nematodes and mites.
Galapagos is also home to marine invertebrates. This very diverse group includes molluscs (e.g., shells and snails), marine annelids (e.g., segmented worms), echinoderms (e.g., sea urchins and sea cucumbers), cnidarians (e.g., corals and gorgonians), sponges, and many others.
Credits: (darwinfoundation.org) Editors: Henri W. Herrera, Lázaro Roque-Álbelo. Other Contributors: Léon L. Baert, Fabián Bersosa, Ruth Boada, Charlotte Causton, Germania Estévez, John M. Heraty, Christopher Hodgson, Bernard Landry, Maria Piedad Lincango, Alejandro Mieles, Christine E. Parent, Stewart B. Peck, Ashley Sheridan, Bradley J. Sinclair, Michael R. Wilson.