Thylacocercus is a genus of vetulocystid from the Wheeler Shale of Utah that is tentatively placed withini the family Vetulocystidae.

[1] Thylacocercus is unlike the Chengjiang lagerstatte vetulocystids from China both in being more recent and in having a crown of what appear to be broad tentacles at the top of its anterior section.

The anterior section is also smooth, lacking the cones and suspected respiratory organ diagnostic of the Chengjiang vetulocystids, although these absences may be artifacts of the preservation of the single known specimen.

If vetulocystids are ancestral to echinoderms, then the tentacles of Thylacocercus could be coleomic structures related to feeding ambulacra.

[1] An analysis focusing on stem chordates was extended to include vetulocystids, and found weak support for them as a monophyletic clade at the base of the chordate stem (contrary to more typical ambulacrarian placements), with the following internal relationships:[3] Thylacocercus Dianchicystis Vetulocystis