''Asterina phylactica'' is a species of

sea star 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 a ...

. It can be found in geographically widespread sites around the British Isles and in the Mediterranean Sea. It has five arms, is about 1.5 cm across and is of a green colour with central brown markings. The species was formally described in 1979 and is very similar to '' Asterina gibbosa''.

Description

''Asterina phylactica'' is a pentagonal starfish with short blunt arms and a flattened shape. It grows to a diameter of about and is olive-green with a central brown star-shaped marking, a pale underside, and a clear cut edge between the upper and lower surfaces. It can be distinguished from the closely related ''Asterina gibbosa'' by the fact that it has fewer plates surrounding its mouth, its smaller size and its characteristic colouring. At one time the two were believed to be the same species but it was realised in 1979 that besides the differences in appearance, the two occupied different ecological niches and had different reproductive methods.

Distribution and habitat

''Asterina phylactica'' is native to the northwestern Atlantic, the Mediterranean and Adriatic Seas. Around the British Isles, ''Asterina phylactica'' is found around the south-west coasts but also occurs on the west coasts of Scotland and north-west Ireland. In Wales, the typical habitat for this species is rock pools on exposed coasts with much encrusting

coralline algae Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of ...

. It is a tolerant species and able to adapt to a range of different salinities and temperatures.

Biology

''Asterina phylactica'' feeds on the film of

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

and diatoms that exists on the surface of rocks. To do this it everts its stomach and presses it against the rock before secreting digestive enzymes. In their first year, individuals of ''Asterina phylactica'' are all males but in the following year they become hermaphrodite and produce both sperm and eggs. The breeding season is late spring and several individuals come together in a group. Sperm is liberated into the sea and the eggs are fertilised. The developing embryos are retained under the starfish where they are brooded for about three weeks. The eggs have direct development and

metamorphose Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some insec ...

into juvenile starfish which crawl out from under their mother and disperse. The lifespan is probably about two years as females normally die after they have brooded their young.

References

{{Taxonbar, from=Q2422338 phylactica Starfish described in 1979