Phylum Arthropoda: General Characteristics and Its Classification
Phylum Arthropoda is the largest animal group which constitutes the largest percentage of the world’s organisms. It is estimated that about 84% of all known species of animals belong to this phylum and number of known species vary between 1,170,000 and 5 to 10 million. Besides these, many arthropods are not yet unidentified. Some prominent groups of arthropods are insects, crabs, spiders, bees, ants, millipedes, shrimps, centipedes, etc. Among them, insects form the single largest class of phylum Arthropoda. According to the entomologist, globally there are over 10 quintillion insects on earth, of which, more than 300,000 species are Coleoptera, 180,000 species belong to Lepidoptera, over 90,000 dipteran species and over 100,000 species belong to Hymenoptera.
The term “Arthropoda” is derived from two Greek words ‘arthros’ meaning ‘joint’ and ‘podos’ meaning ‘leg’. Hence the word “Arthropoda” means “jointed legs”. Arthropods are protostomic, eucoelomic organisms and they have functional segmentation body with a pair of the jointed appendage. They also have a bilaterally symmetrical body with external chitinous cuticle. Some species of arthropods bear wings for aerial movement.
They are the successful animal groups which show a great variety of adaptations. Among them, some live in aquatic environments, some inhabit in terrestrial habitat and others are adapted for aerial habitats.
General Characteristic Features of Phylum Arthropoda
You might also read: Phylum Mollusca: General Characteristics and Its Classification
Classification of Phylum Arthropoda
The phylum Arthropoda is divided into the following five sub-phyla:
Sub Phylum-I: Trilobitomorpha [Gk. tri = three, lobos = lobe, morphe = shape = three-lobed form]
Examples: Triarthrus eatoni, Dalmanites limulurus
Sub Phylum-II: Chelicerata (Gr. chele=claw, keros=horn)
Subphylum Chelicerata is again divided into the following two classes:
Class I: Xiphosura (Gr. xiphos=sword, oura=tail)
Examples: Limulus polyphemus (horseshoe crabs), Tachypleus gigas
Class II: Arachnida (Gr. Arachne =spider)
Examples: Heterometrus cyaneus,
Sub Phylum Myriopoda is divided into the following four classes:
Class-I: Chilopoda (centipedes)
Example: Scolopendra galapagoensis, Scutigera coleoptrata (house centipede)
Class-II: Diplopoda (Millipedes)
Example: Julus terrestris
Example: Pauropus amicus
Class-IV: Symphyla (pseudocentipedes)
Example: Scutigerella immaculata (garden symphylan)
Sub Phylum: Hexapoda
Examples: Musca domestica (housefly), Lepisma saccharina (silverfish)
Subphylum Hexapoda is divided into the following twoclasses:
Class-I: Insecta (insects)
Examples: Pieris balcana (Butterfly), Apis serana
Example: Entomobrya albocincta
Subphylum-V: Crustacea (Crusta: shell)
Class crustacean makes the large group of organisms under phylum Arthropoda. The notable crustaceans include the crabs, crayfish, lobsters, shrimp, barnacles, krill, copepods, ostracods, and mantis shrimp, etc. This class contains over 67,000 known species which are found in freshwater and sea. The American lobster is the largest crustaceans which can grow up to 20 kg in weight while the giant Japanese crab which has legs that can span up to 12 feet (3.7 meters).
Classification of Crustacea
The subphylum Crustacea is divided into the following six classes;
This class is the largest and extremely diverse class which contains over 40,000 species. The notable species include pill bugs, lobster, amphipods, crabs, scuds, crayfish, krill, shrimp, mantis shrimp, etc.
Example: Lysmata amboinensis (Pacific Cleaner Shrimp), Nennalpheus sibogae
Example: Tigriopus brevicornis, Aglaodiaptomus leptopus
Example: Daphnia pulex, Artemia salina (brine shrimp)
Example: Herpetocypris reptans, Stenocypris hislopi
Example: Tesnusocaris goldichi , Cryptocaris hootchi
Example: Chiltoniella elongate, Hampsonellus brasiliensis
Arthropods live on land and in water and they are the source of food for many animals and human being. Many crustaceans species such as crabs, shrimp, prawns, lobsters, crayfish, etc are consumed by humans as protein sources. They are now cultured on a large commercial scale to meet the nutrition demands. Ecologically, they make food chain and also provide an important nutrition source for various animals such as fish, birds, mammals, and mollusks.