Family_tree Spider

shultz (2007) s evolutionary family tree of arachnids – † marks extinct groups.

it agreed spiders (araneae) monophyletic (i.e., members of group of organisms form clade, consisting of last common ancestor , of descendants). there has been debate closest evolutionary relatives are, , how of these evolved ancestral chelicerates, marine animals. cladogram on right based on j. w. shultz analysis (2007). other views include proposals that: scorpions more closely related extinct marine scorpion-like eurypterids spiders; spiders , amblypygi monophyletic group. appearance of several multi-way branchings in tree on right shows there still uncertainties relationships between groups involved.

arachnids lack features of other chelicerates, including backward-pointing mouths , gnathobases ( jaw bases ) @ bases of legs; both of these features part of ancestral arthropod feeding system. instead, have mouths point forwards , downwards, , have means of breathing air. spiders (araneae) distinguished other arachnid groups several characteristics, including spinnerets and, in males, pedipalps specially adapted sperm transfer.