Invertebrates and Fish

Invertebrates are animals without a backbone or bony skeleton. They range in size from microscopic mites and almost invisible flies to giant squid with soccer-ball-size eyes.

This is by far the largest group in the animal kingdom: 97 percent of all animals are invertebrates. So far, 1.25 million species have been described, most of which are insects, and there are millions more to be discovered. The total number of invertebrate species could be 5, 10, or even 30 million, com- pared to just 60,000 vertebrates.

One reason for the success of invertebrates is how quickly they reproduce. Sponges and corals, for example, produce both eggs and sperm. Social insects such as ants and bees lay eggs that can develop without fertilization—they become the workers.

Insects in particular are successful because they are so adaptable. They are opportunistic eaters, feeding on plants, animals, and decaying organic material. They are able to survive in extreme environments, including very hot, dry habitats. And many can fly—either to escape predators or to find new sources of food, water, and shelter.

Like vertebrates, invertebrates are classified based upon their body structure, life cycle, and evolutionary history.

—From the National Geographic

All fish share two traits: they live in water and they have a backbone—they are vertebrates. Apart from these similarities, however, many of the species in this group differ markedly from one another. Fin fish like salmon have gills, are covered in scales, and reproduce by laying eggs. Eels, by contrast, have worm-like bodies and exceedingly slimy skin. Lungfish gulp air. Whale sharks, the largest fish, give birth to live young and eat only tiny fish, squid, and plankton. Some species, such as the weedy sea dragon, are so bizarre they seem almost unreal.

Fish have developed special senses, too. Because water transmits sounds, disperses chemicals, and conducts electricity better than air, fish rely less on their vision and more on their hearing, taste, and smell. Many can detect motion in the water using a special row of scales with sensors known as the lateral line. Others can find their prey and even navigate by detecting electrical charges.

One reason fish are so diverse is that 70 percent of the planet is covered in water. The animals in this group live in a variety of habitats ranging from coral reefs and kelp forests to rivers, streams, and the open ocean. Another is that fish are very old on the evolutionary scale. According to fossil records, they have been on Earth for more than 500 million years! The total number of living fish species—about 32,000— is greater than the total of all other vertebrate species (amphibians, reptiles, birds, and mammals) combined.

—From the National Geographic

For the kind cooperation, I thank the Nature and Acquarissima 2000

The IUCN REDLIST , established in 1948 is the largest database of information on the status of conservation of every animal and plant species of the Planet. The technical and scientific data are collected and analyzed by many expert zoologists and botanists who lend part of their scientific work to IUCN in a totally free way. THANK YOU!

No evaluation was made
At relatively low risk of extinction
It will probably become vulnerable
High risk of extinction in nature
At very high risk of extinction in nature
At extremely high risk
It survives only in captivity
No surviving individual

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