Arthropoda 

major animal phylum which comprises those invertebrates, which have an external skeleton and jointed appendages in contrast to the vertebrates, which are animals with a backbone.

They comprise the most animals with over 870 000 species classified worldwide but still a large number is unknown. In numbers, total mass or distribution they are the most successful animals. The total dry mass, e.g. of ants surpasses by far that of humans. Arthropods developed from soft bodied annelid-kind animals but developed later an external skeleton or cuticle for protection. That skeleton however limits the size of those animals and has to be shed occasionally for growth reasons and then the animals are vulnerable. The senses of arthropods are quite different to those of vertebrates. Antennae function as taste and touch organs and eyes are simple or compound ones and come in pairs or multiples.

Another very distinct trait is that of metamorphosis. The young or larva differs greatly from an adult or imago and different species undergo distinct metamorphosis, from complete ones like the butterflies to shortened or incomplete ones.

The phylum comprises three large sub-phylums, Crustacea, Uniramia and Chelicerata, which will be shown in the tables below

 Sub-Phylum  Crustacea

is comprised by the largest specimens of arthropods, the lobsters (up to 20 kgs). The characteristics of those animals are that they have antennae and a jaw and are mostly found in salt and sweet water.

Class

Representative species

 Sub-Phylum  Chelicerata

are invertebrates which have in common specialized mouth parts and absent antennae and are mostly land dwellers.

Representative species

 Sub-Phylum  Uniramia

has the most species of any animal groups and includes all insects and the myriapods. In the table some of the most important orders are shown.