Invertebrates Facts

  • Invertebrates are multi-cellular and all the cells have different responsibilities to keep the animal alive.
  • Invertebrates have no backbone or bony skeleton or cells wall like all other animals.
  • Invertebrates like echinoderms do not have heads.
  • There are millions of invertebrates living in our house in the name of dust mites which are hardly visible to human eyes.
  • Invertebrates under a process called metamorphosis through which they change form as they grow.



Arachnids are invertebrate animals that belong to the group Arthropods and subphylum Chelicerata. This group includes animals like spiders, ticks, scorpions, and mites. Arachnids get their name after the legendary figure Arachne. They are terrestrial. Arachnids are easily distinguished from the other insects by the fact that they have eight legs.

Fossils studies suggest that arachnids are the fist animal species to live on land early in the Devonian period. Today there are about 65,000 to 73,000 species of arachnids are found. They are found in all parts of the world in the entire habitat. Arachnids species living in the warm, arid tropical region will grow to their greatest size.

Like arthropods arachnids also have a hard exoskeleton and jointed legs used for locomotion. Some arachnids have four pairs of legs. Few of them use their first pair of legs for feeding and to hold the prey. They lack the antennae. The body segment is divided into prosoma and abdomen. To know about more about the body structure of the arachnids refer to the page Anatomy of Arachnids.

Arachnids are antagonistic predators. Their body temperature depends on the temperature of the surroundings hence they are cold blooded animals. Book lung which has the structure of the gills helps them to breathe. Most of the arachnids are carnivores. They pierce the body of the prey and consume the body fluids. You can learn more about the characteristic of the arachnids through the page Characteristic of Arachnids.

Arachnids are predaceous. Usually these species wait for small animal species like insects to hunt them for their prey. They partly of wholly break the prey with the help of secreted fluids and then suck them.

Mites are the largest order of the arachnids. Spiders follow the mites in the order. The mites feed on plants and some mites act as agricultural pests. Ticks are the subgroups of mites and they are blood sucking organisms. Ticks can carry other small organisms that can spread very sever human diseases.

The bites of some arachnids like spiders, scorpions, and stings are really very dangerous. But most of the other arachnids are harmless and they help the nature to build the balance eco system.

Arachnids belong to the class arachnida and to the phylum arthropoda. They can be classified into 11 orders. They are:

  • Acri or Acarina (mites and ticks)
  • Amblypygi (tailless whipscropions)
  • Araneae (spider)
  • Opiliones (dady longlegs)
  • Palpigradi (palpigrades)
  • Pseudoscorpiones (false scorpions)
  • Ricinulei (ricinuleids)
  • Schizomida (micro whipscorpions)
  • Scorpionida (true scorpions)
  • Solpugida (windscorpions)
  • Uropygi (whipscorpions)

To learn briefly about the classifications of each order take a visit to the page Classification of Arachnids

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