Colymbosathon ecplecticos is a fossil ostracod described from a specimen obtained from Herefordshire which is dated to the Silurian (425 Ma).

The generic name is from Greek Kolymbos (swimmer) and sathon (having a large penis) while the species epithet is from ekplektikos meaning "astounding".

Imaging and virtual reconstruction of the fossil showed that the soft parts were well-preserved.

The specimen, a male, was found to have a large copulatory organ.

[1] It is the oldest known specimen with gills among fossil ostracods.