Chimerarachne

[1] Fossils of Chimerarachne were discovered in Burmese amber from Myanmar which dates to the mid-Cretaceous, about 100 million years ago.

These fossils resemble spiders in having two of their key defining features: spinnerets for spinning silk, and a modified male organ on the pedipalp for transferring sperm.

It suggests that there used to be spider-like animals with tails which lived alongside true spiders for at least 200 million years.

[3] The two publications agree on the basic anatomy and significance of these fossils, but differ slightly in the interpretation of their position of Chimerarachne in the arachnid tree of life.

[2] The Huang et al. study placed Chimerarachne a little more distant from spiders and as part of an extinct arachnid order known as Uraraneida which are also spider-like, and have a tail, but which were not previously thought to have spinnerets.

In 2019 and 2022, Wunderlich suggested dividing an order for spiders, Araneida into suborder Araneae and Chimerarachnida, excluding Uraraneida.

Ventral structures of Chimerarachne yingi
1-12: Opisthosomal segment 1-12
Als: Anterior lateral spinneret
Ams: Anterior median spinneret
Ch: Chelicera
L1-4: Coxae of leg 1-4
Lbi: Labium
Pp: Coxa of pedipalp
Pls: Posterior lateral spinneret
St: Prosomal sternite
Te: Telson / Flagellum