of all Earth's animals are invertebrates
World's heaviest invertebrate: the giant clam
Comfortable temperature for deep-sea tube worms
World's largest invertebrate: the giant squid
An invertebrate is an animal without a backbone. Common examples of invertebrates include snails, clams, insects, spiders, and worms. 97 percent of all animals on Earth are invertebrates.
You can find marine invertebrates in almost every marine exhibit. The most familiar invertebrates include crabs, sea anemones, jellies, sea stars, sea urchins, sea cucumbers and shrimps. Even the octopus, one of the most popular attractions at the Aquarium, is an invertebrate.
Invertebrates thrive in a wide variety of habitats worldwide. They exist on every continent, on the ground and in the air, in soil and in water. Terrestrial invertebrates such as the North African desert ant, Cataglyphis fortis, can withstand surface temperatures of more than 67°C. At the other extreme, some invertebrates exist in near-freezing waters. Some marine invertebrates, including tube worms, live on the ocean bottom near vents that expel sulphide-rich water heated to 400°C. Sulphides are poisonous to most animals, but bacteria in the tube worms’ bodies can metabolize hydrogen sulphide so it is actually a food source.
Many invertebrates have shells that protect them from both predators and losing water when they are out of water. Other invertebrates have developed defenses that allow them to survive without shells. Brightly-coloured sea slugs taste terrible to predators, sea anemones possess numerous stinging tentacles and a battery of sharp spines shield the sea urchin’s body.
Many invertebrates have evolved effective defenses, making them dangerous. Scorpions, conesnails and some jellies can deliver a severe sting, while some spiders and even octopuses can bite, if harassed. Mosquitoes and certain snails may carry parasites causing diseases such as malaria, sleeping sickness, schistosomiasis and hookworm disease.
Tiny, drifting animals, called zooplankton, live in the ocean’s surface waters and feed on tiny drifting plants, called phytoplankton. Some invertebrates are carnivorous. For example, jellies and squids often feed on fishes, while octopuses prefer crab dinners on the sea floor. Dog whelks and some sea stars prey on shellfishes, such as clams and mussels, or on barnacles. Some sea snails, chitons and limpets are herbivores that graze on algae, seaweed and other plants. Sea urchins are opportunistic omnivores. They graze on kelp or algae and scavenge the dead bodies of other animals for a meal.
Many carnivorous invertebrates rely on camouflage to surprise their prey. Others scavenge leftovers from the meals of other animals. Some invertebrates are parasites that live in or on other animals and derive nourishment from their host.
Some invertebrates live symbiotically with other organisms. For example, some sea anemones ride on the shells of decorator crabs; the crab provides bits of food for the sea anemone, and the sea anemone protects the crab from octopuses. Another example is the association between sea anemones and clownfish. The clownfish gain protection while the sea anemones get bits of dropped food.
Squids, octopuses and a majority of other invertebrates reproduce sexually by copulation. Other invertebrates use the broadcast method where both male and female gametes are released into the water in enormous quantities and left to unite by chance. Many invertebrates are hermaphroditic, possessing both male and female sex organs, but they don’t usually self-fertilize. They typically look for another individual to exchange sperm with. Others reproduce asexually. Asexual reproduction results in a genetically identical copy of the parent and is characteristic of cnidarians such as corals and hydroids, some sea anemones and certain worms and sea squirts. Some invertebrate species change sex at different periods in their lives. For example, some shrimp species start life as males and later become females.
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