Rare pits attributed to Tremichnus have been found in crinoids from the Silurian of Estonia. The Rhuddanian Tremichnus is the earliest symbiont in crinoid columnals of Baltica. These pits presumably were domiciles of unknown organisms. Tremichnus had a negative effect on the host crinoid as demonstrated by swollen columnals. Tremichnus in the Silurian of Estonia is less common than similar traces in the Silurian of nearby Gotland. The most important aspect of this study is the rarity of this interaction in these samples in contrast to most other samples of comparable age elsewhere. These structures have a very patchy distribution.