Hatena arenicola is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of single-celled

Unicellular organism

A unicellular organism, also known as a single-celled organism is an organism that consists of only one cell, in contrast to a multicellular organism that consists of multiple cells. Historically simple single celled organisms have sometimes been referred to as monads Prokaryotes, most protists,...

 eukaryote

Eukaryote

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

s described in 2006. The species is a flagellate

Flagellate

Flagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...

, and can resemble a plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

 at one stage of its life, in which it carries a photosynthesizing

Photosynthesis

Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

 alga inside itself, or an animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

, acting as predator in another stage of its life. Researchers believe that this organism is in the process of endosymbiosis, in which one organism is incorporated into another, resulting in a completely new life form. Endosymbiosis is the process by which plants diverged from the trunk of the tree of life

Tree of life (science)

Charles Darwin proposed that phylogeny, the evolutionary relatedness among species through time, was expressible as a metaphor he termed the Tree of Life...

.

The algal endosymbiont is a green alga from the genus Nephroselmis

Nephroselmis

In taxonomy, Nephroselmis is a genus of algae. It has been placed in the Pycnococcaceae, although a 2009 study suggests that it should be separated into its own class, Nephroselmidophyceae.-Scientific databases:* * *...

. Unlike a fully integrated organelle, the Nephroselmis alga does not divide along with the host cell. When the host cell divides, one of the daughter cells receives the Nephroselmis cell and the other daughter returns to a heterotrophic lifestyle. The latter behaves like a predator until it ingests a green alga. The alga then loses its flagella and cytoskeleton, while the Hatena, now a host, switches to photosynthetic nutrition, gains the ability to move towards light and loses its feeding apparatus.

The name is from a Japanese interjection meaning roughly "enigma", or "how odd".

External links

• Pictures of Hatena