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Invertebrate Facts | Galapagos Islands Wildlife Guide

Terrestrial invertebrates—crabs, snails and other land animals that lack backbones—represent an estimated 51 percent of the total biodiversity of the Galapagos Islands. They are present throughout the islands in every habitat and play crucial ecological roles as pollinators, links in the food chain, and as nutrient recyclers, which play an important role in soil formation and plant growth.

The ancestors of these oft-overlooked Galapagos residents originally arrived either through active flight or passive drift from the mainland. Once ashore, many species began to adapt to the unique environmental conditions of the archipelago, which eventually resulted in the creation of new, distinct species. It has been estimated that more than half of all terrestrial invertebrate species found here are endemic to the islands, meaning they are found nowhere else.

At low tide, tide pools offer a good opportunity to study marine invertebrates. Starfish, sea anemones, sea urchins, marine snails, barnacles, chitons and limpets are often found. Venture deeper into the water with snorkeling gear to see many more creatures, including sea cucumbers, octopus and corals. If you poke around some of the rocky underwater crevices, you may even encounter lobster. Be careful where you poke though because you may encounter the sea urchin, which has beautiful, iridescent black spines that are long, brittle and needle-sharp.

Sally Lightfoot Crabs and Black Crabs

Perhaps the most photogenic of the invertebrate species is the Sally Lightfoot crab, which is bright red on the top and blue underneath. This colorful character can be found on rocky beaches throughout the archipelago and is particularly striking to behold as it scuttles over black sand and lava.

Also present on rock beaches is a black crab, which blends well with the lava background. These small, well-camouflaged crabs are actually young Sally Lightfoots. The adults, however, are far from camouflaged and must remain alert and vigilant to escape predators. If humans approach them, Sally Lightfoots will immediately dash to safety and are even able to scurry across tide pools by staying on top of the water. If you remain still, crabs will draw near, a technique herons, who prey on Sally Lightfoots, use to their advantage during predation. Keep an eye out for a lava heron waiting motionless amid rocks on the beach. If a crab moves within striking distance, the bird will thrust toward the crab to grab it. If the heron succeeds, he will devour it, but only after shaking it and knocking it against rocks to make its legs fall off.

Ghost and Hermit Crabs

Other crab species inhabit the Galapagos, including the ghost grab, which is a pale, sand-colored creature that stares at you with unusual eyes situated at the terminus of long eyestalks. It leaves a characteristic pattern of sand balls that are seen on most sandy beaches.

Tide pools also support the hermit crab, a crustacean that makes its home by carrying an empty seashell on its back. When a juvenile hermit crab outgrows its protective shell, it finds a larger one and grows into that one. This “moving house” occurs several times before the hermit crab reaches adult size.

Giant Land Snails

Some of the best-known and most interesting endemic species in this group include the giant land snails in the genus Bulimulu. With more than 60 distinct species, they have adapted to inhabit a variety of highly specific microclimates and habitats—similar to how Darwin’s finches have branched out to exploit a variety of different ecological niches.

Header Credit: Patty Potter
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