"Yunnanozoon" may be the oldest known hemichordate. It is similar to the form "Yunnanozoon", which is possibly a hemichordate. One species, Yoda purpurata, is also the first known hermaphroditic hemichordate. Other well-documented organisms include the crustacean "Belotelson" and the possible hemichordate "Etacystis". More recently, it has been treated as a hemichordate. The Mid Cambrian fossil "Rhabdotubus johanssoni" has been interpreted as a pterobranch hemichordate. Planctosphaera pelagica is a hemichordate and the only known representative of the class Planctosphaeroidea. The epidermis of hemichordate is ciliated whereas it is nonciliated in chordates. Some hemichordate species can have as many as 200 gill slits. This worm-like enteropneust hemichordate led to his interest in vertebrate origins.