Organisms who have hardly changed since their earliest fossil discovery

Rhyniognatha hirsti (Rhyniella praecursor) Springtail.

Dating at 400 million years ago is the oldest fossil insect found so far (a springtail).

The head part of a specimen, preserved in a fragment of Rhynie Chert, was collected in 1919 by the Reverend W. Cran, who provided it to S. Hirst, S. Maulik and D.J. Scourfield. Hirst and Maulik published a report in 1926; in it they described Rhyniella praecursor, which is now known to be a springtail.

Springtails are attested to since the Early Devonian.^[12] The fossil from 400 million years ago, Rhyniella praecursor, is the oldest terrestrial arthropod, and was found in the famous Rhynie chert of Scotland. Its morphology resembles extant species quite closely.

Harvestmen spiders

300 million years ago: Harvestmen spiders (European daddy long legs) were much the same as today.

Daddy longlegs have been skittering around the Earth for more than 300 million years, as confirmed by the discovery and imaging of two species that lived in the forests of what is now France before the time of the dinosaurs.

Detailed 3-D reconstructions of the two species reveal that they look surprisingly similar to modern daddy longlegs, which are also known as harvestmen and commonly mistaken for spiders. Each had eight long legs and a flat, circular body, spanning about 0.4 inches in length.

"It is absolutely remarkable how little (that) harvestmen have changed in appearance since before the dinosaurs," study researcher Russell Garwood, of Imperial College London, said in a statement. "If you went out into the garden and found one of these creatures today, it would be like holding a little bit of prehistory in your hands."