''Oikopleura dioica'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of small

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It 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 ca ...

found in the surface waters of most of the world's oceans. It is used as a

model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...

in research into

developmental biology Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of Regeneration (biology), regeneration, asexual reproduction, metamorphosis, and the growth and di ...

Description

''Oikopleura dioica'' is a bioluminescent species. Like other Oikopleuridans, ''O. dioica'' have a discrete body and tail as adults and retain their

notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...

throughout life. They resemble

tadpole A tadpole is the larval stage in the biological life cycle of an amphibian. Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial. Tadpoles have some fish-like features that may not be found i ...

s in appearance with a body typically between long and a tail about four times that length. Its body is ovoid and the tail slender. There are two sub-chordal cells outside the central core of muscle in the tail, which are easily observable some half to two thirds of the way down the length of the tail. The mouth has a small lower lip and the buccal glands are small and globular. The

endostyle The endostyle is an anatomical feature found in invertebrate chordates and larval lampreys. It is an organ which assists chordates in filter-feeding. It is found in adult urochordates and cephalochordates, as well as in the larvae of the vertebra ...

is large, extending nearly as far as the anus. The right lobe of the stomach forms a sac behind the entrance to the intestine. ''O. dioica'' sexes are separate, unlike in all other known appendicularians, and the ovary or testes are at the rear of the body.

Distribution

''Oikopleura dioica'' is widely distributed over the continental shelf in tropical and temperate waters in all the world's oceans. It is very abundant in surface waters but in colder seas is replaced by '' Oikopleura vanhoeffeni'' and ''

Oikopleura labradoriensis ''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 par ...

''.

Behaviour

Every three or four hours, ''Oikopleura dioica'' creates a mucus net "house" which surrounds its body. Water is pumped through this house and minute food particles are filtered out of the water and then transferred into the mouth. Once the gelatinous net "houses" are too clogged to allow further filtration, they are then abandoned and drift down through the water to the seabed as "marine snow".

Use in research

''Oikopleura dioica'' is used as a

, a role for which it has several features to recommend it. It has the typical

chordate A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fiv ...

body plan, it is simple to keep and breed in the laboratory, it produces large numbers of eggs and the

generation time In population biology and demography, generation time is the average time between two consecutive generations in the lineages of a population. In human populations, generation time typically ranges from 22 to 33 years. Historians sometimes use this ...

is only four days at . The body is also transparent, making it easier to study, and at hatching only consist of 550 cells. The genome has been sequenced and contains about 15,000 genes, approximately half the number occurring in vertebrates. All central

Hox gene Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the cor ...

s have been lost. Comparison of the genome with that of other chordates will help identify the genes which appeared early in the vertebrate lineage. In the

Sars International Centre for Marine Molecular Biology The Sars International Centre for Marine Molecular Biology is a research establishment located at Bergen in Norway. History Sars International Centre for Marine Molecular Biology was established in April 1997. It is located at the Bergen High Tech ...

, inbred lines have been developed using repeated matings of closely related individuals. The molecular base of a number of aspects of vertebrate development is identical in these simple chordates and in higher vertebrates. As an example, the

brachyury T-box transcription factor T, also known as Brachyury protein, is encoded for in humans by the ''TBXT'' gene. Brachyury functions as a transcription factor within the T-box family of genes. Brachyury homologs have been found in all bilaterian a ...

gene and the

homolog In biology, homology is similarity due to shared ancestry between a pair of structures or genes in different taxa. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of prima ...

of the

PAX2 Paired box gene 2, also known as Pax-2, is a protein which in humans is encoded by the ''PAX2'' gene. Function The Pax Genes, or Paired-Box Containing Genes, play important roles in the development and proliferation of multiple cell lines, dev ...

gene both play a similar role in the development of tunicates as they do in vertebrates. Complex aspects of vertebral development such as the differentiation of the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

can thus be studied in the laboratory.

References

External links

ANISEED
the Tunicate model organism database
OikoBase
A curated genome expression database of Oikopleura dioica {{Taxonbar, from=Q10505290 Appendicularia Animals described in 1872 Animal models Animal developmental biology Bioluminescent animals