What living creature is most difficult to fossilize?

Soft-bodied organisms are generally the most difficult to fossilize because they lack hard parts like bones or shells that are more likely to withstand the conditions necessary for fossilization. Examples include jellyfish, worms, and certain types of fungi, which decompose rapidly after death and leave little to no trace. Environmental factors, such as sedimentation rates and conditions that promote decay, further complicate the fossilization process for these creatures. Consequently, soft-bodied organisms are often underrepresented in the fossil record.