''Planctosphaera pelagica'' is a

hemichordate Hemichordata is a phylum which consists of triploblastic, enterocoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and inclu ...

and the only known representative of the class Planctosphaeroidea. The species is known only by its free swimming larvae. The larvae are

tornaria A tornaria is the planktonic larva of some species of Hemichordata such as the acorn worms. It is very similar in appearance to the bipinnaria larvae of starfishes, with convoluted bands of cilia The cilium, plural cilia (), is a membrane ...

larvae similar to those of the closely related

Enteropneusta The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. The closest non-hemichordate relatives of the Enteropneusta are the echinoderms. There are 111 known species of acorn worm in ...

, which possess a ciliated band to capture food particles. ''Planctosphaera pelagica'' is unique in possessing mucus secreting glands around the ciliated band. Possible uses of the mucus glands include assisting in feeding or deterring predators and parasites. ''Planctosphaera pelagica'' larvae are also larger than enteropneust larvae. It is due to the mucus glands and size difference they are usually given their own class.

References

Animal genera Monotypic animal genera {{Hemichordate-stub