Wikipedia
Oikopleura is a genus of Tunicata (sea-squirts) in the class Appendicularia. It forms a mucus house every four hours at 20 degrees Celsius. This house has a coarse mesh to keep out big particles, and a fine mesh that collects the small particles, down to the nanoplankton that includes (pelagic) bacteria.
Abandoned mucus houses sink to the deep, collecting organic particles during their descent. They make an important contribution to marine snow, since Oikopleura is abundant and is a very active filterer, using powerful strokes of its tail. Its abundance is less obvious from preserved samples (that are usually analyzed) because the gelatinous body disappears in the preservation process while leaving hardly any trace.
Species of ''Oikopleura ''have the smallest genomes in the animal kingdom, only about 75 Mb.