You may have an appendicularian or ascidian larva.

Ascidians and appendicularians are tunicates belonging to the phylum Chordata. They are characterized by a round body and long tail. Below are some commonly found in this region.


Ascidians


Ascidians are meroplankton, in that only their tadpole larvae exist in the plankton, while the adults are benthic.


Tadpole larvae


Presettlement adult form

Appendicularians


Appendicularians resemble the "tadpole larvae" of benthic tunicates and produce unique, temporary gelatinous "houses" to filter small plankton for food.

Oikopleura dioica


Appendicularia sicula


Fritillaria spp.