Araneomorphs are the so-called modern spiders, having evolved later than the earliest spiders, the mygalomorphs. They are only modern in the sense of their more recent lineages, as living mygalomorphs must also be modern in the sense of being alive today. Araneomorphs have various characteristics which separate them from the mygalomorphs, which include having only one pair of book lungs and sometimes breathing tubes, whereas mygalomorphs have two pairs of book lungs. As a result mygalomorphs are restricted to moist environments with more or less constant access to water, while araneomorphs are more free living. There are many missing link spiders between the two groups.