Arthropods Characteristics

One of the biggest family in kingdom Animalia, Phylum Arthropoda boasts of more than a million members, which constitute approximately one-fourth of the known living organisms on the planet. Their prominent characteristics include an external skeleton (exoskeleton), segmented bodies and six or more joint legs. The members of this family, known as arthropods, include species like the spiders, scorpions, beetles, shrimps, bees, crabs, butterflies and several other organisms.

The unique characteristics of arthropods have helped them to survive the extremes of the planet since a long time. These organisms exist everywhere - right from the high altitude of the mountainous regions (spiders and beetles) to the dark depth of the oceans (crabs and shrimps). While some arthropods are smaller than a centimeter, others like the King Crab can grow on to attain an average length of around 1 foot or more.

Arthropods Characteristic Traits

Other than the segmented body, exoskeleton and multiple pairs of legs, the general characteristics of arthropods include the dorsal heart, hemocoelic body cavity and a nervous system made up of the dorsal brain and ventral nerve chord. On the basis of the physical characteristics of arthropods, they can be divided into five major classes - Archinda, Crustacea, Diplopoda, Chilopoda, and Hexapoda. The characteristic traits of each of these classes of arthropod are given below.

Class Archinda: Spiders and scorpions are the most popular members of this class of the arthropods. Their body is segmented into two regions - the cephalothorax, with 6 pairs of appendages, and abdomen, with 3 pair of appendages. The organisms belonging to this class are terrestrial, however, some of them do display secondary aquatic traits, though rarely. A high degree of predation is witnessed in the arachnid species.

Class Crustacea: Crabs and shrimps belong to this class of the arthropods. Crustaceans have a body structure similar to the arachnids, i.e. segmentation into two parts - cephalothorax and abdomen. What differs the two classes is the fact that the crustaceans are predominantly aquatic, with a few species displaying secondary terrestrial traits, unlike their arachnid counterparts. These species are predominantly scavengers, but do display predatory behavior at times.

Class Diplopoda: This class of arthropods includes millipedes, typically characterized by a cylindrical body, featuring around 20 to 100 segments, with each segment having two pairs of legs. They also sport a pair of antennae and compound eyes on their head. All the subspecies of millipedes are herbivorous, and terrestrial in nature.

Class Chilopoda: This class of arthropods includes centipedes, typically characterized by a flattened body, with 15 to 173 segments, and each segment having a single pair of legs. Although centipedes do resemble millipedes to some extent, both the species have stark contrast as far as behavior is concerned. The most prominent difference is the fact that the millipedes are herbivorous in nature, whereas the centipedes are carnivorous. Its first trunk appendage, which is modified into venomous claws, compliments its predatory behavior quite well.

Class Hexapoda: This class of arthropods includes a range of insect species, typically characterized by a body with three segments - the head, thorax and the abdomen. The head has five pairs of appendages, thorax has 3 pair of legs and 2 pairs of wings, and abdomen has a single pair of appendage. Most of these insects are terrestrial, while a few are semi-aquatic. These organisms have a range of feeding strategies, which differ from species to species. The organisms belonging to this class have the distinction of being the only invertebrates with wings.

Even though more than a million species of arthropods have been documented so far, scientific estimates suggest that several more still remain undiscovered. It is virtually impossible to find the number of species of arthropods that inhabit the regions like the Amazon or the Southeast Asian rainforests. If the ongoing efforts to identify and document these species are successful, we are bound to come across some new characteristic traits which will make this family of kingdom Animalia all the more interesting.