Spiders of the ecribellate haplogyne family Caponiidae are unusual in a number of ways. They differ from other spiders in lacking book lungs and having the posterior median spinnerets anteriorly displaced to form a transverse row with the anterior lateral spinnerets. Most species have only two eyes, which is also unusual among spiders. A few species of Caponiidae variously have four, six or eight eyes. In some species the number of eyes will increase when the spiderling changes its skin as it grows towards adulthood.