It is believed that the number arthropods on the planet far exceeds the number of all the other members of the animal kingdom put together. In fact, the Amazon rainforest alone is estimated to house a million arthropods, some of which are waiting to be discovered. Also interesting is the fact that it's a highly diverse group in terms of size, with some species measuring less than a centimeter and some going on to attain a length of 1 foot at full growth.
An Introduction to Arthropods
The members of Phylum Arthropoda, commonly referred to as the arthropods, are invertebrates which are typically characterized by an external skeleton (exoskeleton), a segmented body, and six or more joint legs. With more than a million species to its credit, it is by far the biggest group in the animal kingdom. Other than the general characteristics we mentioned, there are certain unique characteristics that are restricted to some species of this family.
We often refer to spiders and scorpions as insects, which is technically incorrect, as they belong to the class Arachnida―a suborder of arthropods. Insects, on the other hand, belong to the class Hexapoda, which is a totally different suborder of this phylum. Each of the suborders has certain characteristics of its own which differ it from the other suborders.
The members of the Arachnida suborder, for instance, have a body which is segmented into two regions, the cephalothorax and abdomen. Similarly, the members of the Hexapoda suborder boast of being the only invertebrates with the ability to fly. There are several other facts about arthropods, which sadly, are restricted to zoology journals.
Interesting Facts about Arthropods
- Classified as a millipede, Pneumodesmus newmani, which inhabited the planet 428 million years ago, is considered the oldest land animal on the Earth.
- Each of the segments of an arthropod's body is specially designed to facilitate particular functions, including feeding, sensory perception, visceral functions, etc.
- Of the entire lot of arthropods, spiders have the most centralized nervous system.
- With a body length of 16 inches and an approximate weight of 9 lbs, the coconut crab is the largest arthropod in the world.
- In terms of leg span, the Japanese spider crab is the largest arthropod, with a leg span of 12 feet 6 inches when fully stretched.
- While internal fertilization is common in arthropods, some aquatic arthropods undergo external fertilization.
- Even though most of the arthropods lay eggs, in scorpions, the eggs hatch inside the female's body and it gives birth to young ones.
- The Amazonian giant centipede is the largest centipede in the world. It can grow to a length of 30 cm.
- The giant African millipede is the largest millipede in the world, with an average length of 28 cm.
- Arthropods are subjected to a biological process referred to as metamorphosis, wherein their body form and physiology undergo a radical transformation from egg stage to larva, pupa, and adult state.
There is no questioning the fact that this phylum is one of the most amazing attributes of the Earth's ecosystem. Like we said, several arthropod species are waiting to be discovered in various biomes of the world, so our chances of coming across a range of new facts about the members of this phylum cannot be ruled out.