Invertebrates were the first animals to evolve. The first animals had soft bodies and for this reason they left little fossil evidence of their existence. Scientists have discovered fossilized burrows and tracks in sediments that date back nearly 1 billion years. The oldest fossil of an invertebrate dates back to the late precambrian, about 600 million years ago.
What percentage of known animals on earth are invertebrates? Over 95%. Invertebrates defy nearly every generality. Of some 30 phyla representing 95 to 99 percent of the planet's animal species, the only thing they have in common is what they lack: a backbone.
The simplest invertebrates, in fact the simplest animals, are sponges. Sponges are sessile animals that live in marine and freshwater habitats. Sponges feed by siphoning water into their body and filtering out food particles. Water enters their body through small pores on their outer surface. The water then passes into a central cavity and is expelled through a large opening called the osculum. Although the cells in the body of a sponge perform specialized functions, they are not organized into true tissues or organs as they are in other animals.
The delicately latticed Venus' flower basket sponge,Euplectella aspergillum, often shelters pairs of shrimp and as a result was once a symbol of marital fidelity in Japanese weddings
They have no brains and no spines. You can often see right through them. But they can cause painful, sometimes deadly stings. Some can even glow in the dark! Scientists know them as medusas, but most people call them jellyfish.
The joined exoskeletons of tiny cnidarians called polyps form coral reefs. Coral reefs provide habitat to more than one fourth of marine animal species including fish, anemones, cephalopods, crustaceans, and sponges. Coral reefs also benefit humans by protecting seashore communities from strong waves and storms.
The longest invertebrate is the ribbon worm which can grow to 180 feet long.
The smallest invertebrate is the rotifer, or wheel animal, which can be as small as 50um.
Many of the world’s parasites are invertebrates. Ticks, tapeworms, leeches, and roundworms are just a few of the parasites in the animal kingdom and all are invertebrates. Some parasites live on the external surfaces of their hosts while others live in the digestive tract or tissues of their hosts. Parasites often go through an elaborate series of steps in their life cycle during which time they may pass from one to several other hosts.
They can’t see or hear. They hide from daylight. They have no eyes, no ears, no arms, and no legs. Yet they work the soil as hard as any farmer. What are they? Earthworms. Earthworms enrich the soil by eating dirt, literally. To burrow, earthworms may simply wiggle through the ground, but compact earth requires them to swallow the soil.
Around 23% of all marine organisms are mollusks.
Mollusks have variously modified shells, ranging from the large, whorled shell of the whelk to the thin vestigial plate embedded in the body of a slug. Conchology is the study of mollusk shells.
Did you ever eat a quahog? A quahog is not a pig. It is a kind of clam. Quahog is a name that Native Americans gave clams.
The only hard body part of an octopus is a hooked beak at the end of its tentacles.
The biggest invertebrate is the giant squid. It can be up to 60 feet (18 meters) long. Recently, Watch Video)Architeuthis dux (
Lobsters, crabs, and shrimp all have 10 legs. The front two legs have pincers they can use to catch food and fight off predators.
Some scorpion mothers protect their young by carrying them on their backs.
Try to picture an animal that is almost all mouth and arms. Its arms are covered with feet, and it has no brain. This strange and wonderful sea animal is called a starfish. Another name for starfish is sea star. The starfish is not a fish. It is an echinoderm. Starfish and other echinoderms have sharp, hard spines sticking up from their skin. Brittle stars, sea cucumbers, sand dollars, and sea urchins are other kinds of echinoderms.
The fleshy, oblong sea cucumber is radially symmetrical at the organ level only. They are some of the gutsiest echinoderms, spewing out their organs when disturbed and regenerating them over several weeks in a process called evisceration.
The hard exoskeletons of insects and creatures such as crabs do not grow with the rest of the body. As the animal grows, its exoskeleton gets too tight—so it sheds it from time to time. Underneath is a new, slightly bigger, and looser case. The animal pumps itself up with fluid before the case has time to harden.
Most invertebrates change form as they grow, going through a process known as metamorphosis. Metamorphosis is a process by which organisms change form as they mature. Young are sometimes very different from adult forms and may feed on different resources and inhabit different niches. Metamorphosis can enable a species to disperse with greater ease at certain times during its life cycle, find different food resources, or prepare for breeding. The changes involved in metamorphosis are controlled by hormones and may proceed quickly or gradually.
Insects are invertebrates, or animals without backbones. They breathe air through holes in their bodies. The body of an insect has three main parts called the head, thorax, and abdomen.
There are likely millions of invertebrates living in your house right now. They are called dust mites and you can't see them.
Queen Alexandra's Birdwing is the biggest butterfly in the world. Its wingspan is about 1 foot (30 cm) wide.
Centipedes are carnivores which eat insects and worms. They have a poisonous bite to help them kill their prey. Millipedes are herbivores who eat plants and rotting material.
Birds commonly feed on spiders, but the world's largest spider, the Goliath bird-eating tarantula (Therophosa leblondi), turns the tables on avian predators. The tarantula will eat young birds on occasion, although its usual diet consists of frogs, beetles, or small snakes.