''Oikopleura'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

tunicate Tunicates are marine invertebrates belonging to the subphylum Tunicata ( ). This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

s in the class Appendicularia (larvaceans). 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 Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

. Abandoned mucus houses sink to the deep, collecting organic particles during their descent. They make an important contribution to

marine snow In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...

, 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. ''Oikopleura'' contains

bioluminescent Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some fungi, microorganisms inc ...

species. About half of ''Oikopleura'' species are bioluminescent.

Etymology

The genus name comes from ''oikos'' (meaning "house") and ''pleura'' ("rib", or "side of the body"), referring to their ability to build a mucus house like other larvaceans.

Taxonomy

Phylogeny

''Oikopleura'' has been found to possibly be paraphyletic with respect to several other oikopleurid genera, namely: '' Folia'', '' Stegosoma'', '' Mesoikopleura'', and '' Megalocercus''. The genus might also harbour more diversity than thought, with

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

es like '' Oikopleura dioica'' comprising several reproductively incompatible clades despite consistent general morphology.

List of species

Distribution

The oikopleurids are distributed in the tropical waters of all oceans and seas of the globe, having been reported widely in the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

and the western coasts of the

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

''Oikopleura dioica''

A species of particular interest under this genus is the '' Oikopleura dioica'', which is an anomaly among

chordates A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies) that distinguish them from ot ...

. It has retained the fundamental body plan of the chordate; yet, it has lost the mechanism for

retinoic acid Retinoic acid (simplified nomenclature for all-''trans''-retinoic acid) is a metabolite of vitamin A1 (all-''trans''-retinol) that is required for embryonic development, male fertility, regulation of bone growth and immune function. All-''trans ...

signaling which operates during chordate development. The loss raises the question of the evolutionary constraints that have prevented similar changes in the other chordates. ''Oikopleura dioica''

hox gene Hox genes, a subset of homeobox, homeobox genes, are a gene cluster, group of related genes that Evolutionary developmental biology, specify regions of the body plan of an embryo along the craniocaudal axis, head-tail axis of animals. Hox protein ...

s are distributed in nine locations around the genome whereas other

chordate A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies) that distinguish them from ot ...

s have a cluster of hox genes. Of note, this is the first chordate among the eukaryotes found to have

operon In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splic ...

References

External links

Integrated Taxonomic Information System (ITIS): ''Oikopleura'' Taxonomic Serial No.: 159668

National Center for Biotechnologu Information (NCFI): ''Oikopleura'' Taxonomy ID: 34763

''Oikopleura'' Genome Browser

Merriam-Webster: ''Oikopleura''

Videos

Youtube: Larvacea (''Oikopleura dioica'')

Photos

Flickr: Oikopleura sp. in the house
{{Taxonbar, from=Q3639186 Oikopleuridae Tunicate genera Bioluminescent animals