''Orchitophrya stellarum'' is a species of single-celled marine

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

s, a member of the class

Oligohymenophorea The Oligohymenophorea are a large class of ciliates. There is typically a ventral groove containing the mouth and distinct oral cilia, separate from those of the body. These include a paroral membrane to the right of the mouth and membranelles, ...

. It is found living freely in the north Atlantic and Pacific Oceans but is also

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

, being found inside the

gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...

s of

starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...

Biology

''Orchitophrya stellarum'' tolerates a sea temperature range of between and and a

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

range of between 2 and at least 30 parts per thousand of salt equivalent. The lower the temperature, the lower the acceptable level of salinity. Growth is most rapid at 24 °C. It is a facultative parasite of sea stars in the

Asteriidae The Asteriidae are a diverse family of Asteroidea (sea stars) in the order Forcipulatida. It is one of three families in the order Forcipulatida. Genera The World Register of Marine Species lists these genera within the family Asteriidae (in a ...

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

. It seems to be able to survive in the open sea indefinitely as long as there is a supply of bacteria and tissue detritus on which it can feed.

Parasitism

''Orchitophrya stellarum'' is often associated with sea stars and other invertebrates, living on their outer surface and feeding on sloughed-off epidermal tissue. It only appears to become parasitic when the male host starfish has ripe gonads. It probably enters the starfish through the

gonopore A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects have a single common gonopore, except mayflies, which have a pair of gonopores. More specifically, in the unmodified female it is the ...

s, the orifices where gametes are released. There may be a

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

that alerts it to the fact that the testes are ripe and causes it to change its behaviour. As different species of starfish breed at different times of year, ''Orchitophrya stellarum'' may move from one species to another in accordance with their reproductive cycles. In the Pacific Ocean, it may alternate between parasitising '' Evasterias troscheli'' and ''

Pisaster ochraceus ''Pisaster ochraceus'', generally known as the purple sea star, ochre sea star, or ochre starfish, is a common seastar found among the waters of the Pacific Ocean. Identified as a keystone species, ''P. ochraceus'' is considered an important indi ...

'' during the spring and summer and ''

Leptasterias ''Leptasterias'' is a genus of starfish in the family Asteriidae. Members of this genus are characterised by having six arms although five-armed specimens sometimes occur. ''L. muelleri'' is the type species. The taxonomy of the genus is confus ...

spp.'' in the winter. In the Atlantic Ocean, the winter host may again be ''Leptasterias spp.'' but the spring and summer hosts are likely to be ''

Asterias forbesi ''Asterias forbesi'', commonly known as Forbes sea star, is a species of starfish in the family Asteriidae. It is found in shallow waters in the northwest Atlantic Ocean and the Caribbean Sea. Description left, Underside of ''Asterias forbesi'' ...

'' and ''

Asterias rubens The common starfish, common sea star or sugar starfish (''Asterias rubens'') is the most common and familiar starfish in the north-east Atlantic. Belonging to the family Asteriidae, it has five arms and usually grows to between 10–30 ...

''. The ciliate has been found in the testes of all these species. When inside the gonad, it phagocytoses the sperm thus rendering the starfish infertile. Researchers have found skewed sex ratios of affected populations with fewer males than females being found, and males being consistently smaller than females. The researchers thought it likely that there was increased mortality among infected males. In 2006, a mass die-off of the purple sea star (''Pisaster ochraceus'') occurred off the coast of British Columbia. Parasitism by ''Orchitophrya stellarum'' was considered to be the likely cause. A marine parasite expert stated that the starfish was an important member of the marine community and that if it were removed, marine

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

in the area would be threatened. In a study published in 2013, Ochitophrya stellarum, the parasitic ciliate, was discovered in 2007 in the tissues of blue crabs. Hemolymph smears showed the ciliates of the parasite. This was surprising, because ochitophrya stellarum was previously only associated with infecting sea stars. This opportunistic pathogen was responsible for a number of histophagous scuticociliate infections in the blue crabs. The infections were present in the hemal sinuses of all tissues of the blue crabs and in between muscle fibers.

Use as a biological control

The north Pacific sea star, ''

Asterias amurensis ''Asterias amurensis'', also known as the Northern Pacific seastar and Japanese common starfish, is a seastar found in shallow seas and estuary, estuaries, native to the coasts of northern China, Korea, far eastern Russia, Japan, Alaska, the Aleu ...

'', was first seen in Tasmania in 1986 and is spreading along the coasts of southern Australia. It is considered an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

that is threatening local biodiversity.

Biological pest control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

of the starfish is being considered through the introduction of ''Orchitophrya stellarum'', however its ability to regulate sea star populations is uncertain.

Biology

Parasitism

Use as a biological control

References

Further reading