The Ygath is a shipset created for Space Empires IV in 2001 by Andrés Lescano. The Ygath are crystalline creatures who are symbiotically connected to their homeworld. Their preferred planets are airless rock worlds. The Ygath have a good AI, created by Deathstalker, that uses both crystalline and organic technology. There seem to be versions of the AI in circulation for SEIV 1.49, 1.67 and possibly others.
Note that only the versions of the Ygath of 1.4 and above feature Andrés' images. It seems that earlier versions used a different image set.
The Ygathian shipset includes a Troopinfantry Neostandard image.