Why phylum arthropod is called arthropod?

Answer 1

Arthropoda are the most diverse and arguably the best distributed in species, with the highest count known of described species in any phylum. Over a million species under the phylum have been described and biologists estimate that millions of species have yet to be described. Most of these are in the Insecta class; and about 400,000 of them are beetles (coleoptera).

The actual count of living arthropods at any given moment on Earth is unknown but some estimates place them around ten quintillion (10,000,000,000,000,000,000) which is over a billion for every human. By count, insects are over half of all living animals and by some estimates may constitute up to ninety percent of all living animals on the earth. In biomass, krill (an arthropod crustacean) are believed to have the highest of any animal, weighing in from up to half to three quarters of a billion tonnes, and thus having a huge significance in the food chain.

Answer 2

By count the most arthropod species fall under the Insecta class, with a million species described and millions estimated yet to be described. By count, insects are over half of all living animals and by some estimates may constitute up to ninety percent of all living animals on the earth.

In biomass, krill take the top spot weighing in from up to half to three quarters of a billion tonnes, and thus having a huge significance in the food chain.

Answer 3

The largest arthropods are usually crustaceans in part because of physical limitations imposed by the gas exchange, and specifically oxygenation strategy of terrestrial arthropods. Because they do not have lungs, they rely upon gas diffusion through pores (spiracles) open to the air, evident on the exoskeleton in pairs on body segments. These connect to tubules directly connected to body tissues. The strategy is only effective for sizes where the surface area to volume ratio is very high, like in the small body of an insect; this oxygenation strategy would not be effective for larger organisms like humans where the surface area to volume ratio is vastly lower - hence we use specialized gas exchange method utilizing lungs (an organ which greately increases the surface area across which gas exchange occurrs) and a separate branch of the circulatory system dedicated only to oxygenation. Observation of perched insects such as bees sometimes reveals a technique used to compensate for this gas exchange problem - they bob their abdomens and this helps to push gas through the tubules (trachea/tracheoles) and eliminate gaseous waste.

By contrast, the marine arthropods such as crustaceans use gills; this not only compensates for the insect problem of low speed of gas diffusion but also provides a method to mitigate their highly toxic byproduct of nitrogen metabolism (ammonia) by dissolving it in water - something not possible for their terrestrial arthropod counterparts. Hence, a larger size is practical.