What are small arthropods?

On the biological ruler, arthropods tend towards the small end of the spectrum, owing to physical limits imposed by their methods for respiration, gas exchange and circulatory system; a high surface area to volume ratio serves them quite well on these counts.

The smallest arthropods known are a crustacean parasite, Stygotantulus stocki, around a hundred micrometers long (about 4 thousandths of an inch).