The protura are primitive insects. They are so small that most people have never seen them and the only common name for the group is conehead because of the shape of their heads. They weren’t even recognised and described by science until 1907. They have six legs and three body parts: head, thorax and segmented abdomen. There are over five hundred species world wide. All are small, between a half to two and a half millimetres in length. They are white and have no antennae. Instead they use their first set of legs to feel the ground in front of them. Protura also have no eyes but they do have a single sensory organ on the head known as a pseudoculus which is probably sensitive to light.
Protura belong to the most primitive group of insects, the Apterygota, because they have no wings. There are insects that show the beginnings of wings in early development and then lose them secondarily, such as the lice and fleas. The four Apterygote orders, Protura, Diplura, Thysanura and Collemrbola, never develop wings at all. For this reason, it is believed that they are the most primitive insect groups, having evolved before wings.
Some taxonomists think they should not be considered insects at all but placed in the superclass Hexapoda instead. Others are content to leave them in the Class Insecta. Further studies, particularly of their DNA, are needed to make a final decision. One major difference between proturans and other insects is that proturans add segments posteriorly to the abdomen as they grow (anamorphosis). They begin life with 8 abdominal segments and end up with eleven or twelve. This occurs in no other insect group. Another major difference is the presence at the end of the abdomen of a telson, a type of tail common in Crustaceans but found on no other type of insects. The telson may be used for defense. Coneheads have been seen to raise the telson and secrete a sticky substance when threatened by predators. These are intriguing differences that warrant further study.
Coneheadsare saprophytic, eating dead organic matter and fungi. Some may also eat other insects. They have primitive sucking mouthparts used to extract the juices from fungal hyphae and other plant materials. Most live in the top ten centimetres of soil. Those that live deeper tend to have shorter legs than the surface dwelling species. The soils need to be moist to support proturans. Some species can also be found in moss and under the bark of trees.
Very little is still known about the behaviour and life cycles of these little animals. Eggs hatch into immobile immature stages that resemble the adults. Being arthropods, they must moult in order to grow and mature. It is not known if they continue to moult after reaching sexual maturity. Proturans practice indirect fertilization. The male deposits a spermatophore which is then picked up by the female. There is obviously a lot more to be learned about these strange little creatures.
To find out more: http://www.earthlife.net/insects/protura.html
http://www.discoverlife.org/20/q?search=Protura
