The sun star ''(Heliaster helianthus)'' is a species of

Asteroidea 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 ...

(starfish) in the family

Heliasteridae The Heliasteridae are a family of Asteroidea (sea stars) in the order Forcipulatida. It includes two genera: ''Heliaster'' from the East Pacific (California to Chile, including offshore islands), and ''Labidiaster'' from southernmost South Ameri ...

. It is found in shallow water rocky habitats and in the

kelp forest Kelp forests are underwater areas with a high density of kelp, which covers a large part of the world's coastlines. Smaller areas of anchored kelp are called kelp beds. They are recognized as one of the most productive and dynamic ecosystems on Ea ...

s off the Pacific coast of Ecuador, Peru and Chile.

Description

''H. helianthus'' is a multi-armed starfish, the number of arms usually being in the range 28 to 39, and the diameter typically being between . The aboral (upper) surface is brown with reddish tubercles while the oral (under) surface is white or yellowish-white. The disc is broad and the ossicles (plate-like components in the skin) in the

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

parts of the arms (closest to the disc) are connected to those of the neighbouring arms by

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

, forming inter-arm septa. This means that only a small part of each arm is free, the rest appearing to form part of the disc.

Distribution and habitat

This species is present in the southeastern Pacific Ocean, along the west coast of South America. Its range includes Ecuador, Peru and Chile, and it is the only species in its genus present in Chile where it is easily observed on rocks in shallow water.

Ecology

''H. helianthus'' is preyed on by the starfish '' Meyenaster gelatinosus''. In general, small individuals are eaten whole and large individuals are immune from attack, but medium-sized individuals lose arms by

autotomy Autotomy (from the Greek language, Greek ''auto-'', "self-" and ''tome'', "severing", wikt:αὐτοτομία, αὐτοτομία) or self-amputation, is the behaviour whereby an animal sheds or discards one or more of its own appendages, usual ...

. Having trapped its prey, ''M. gelatinosus'' everts its stomach over several arms of its victim, which become autotomised in response to the predation. When this happens, the arms do not detach at the point where they become free, but higher up at their bases; at the same time, a split occurs along the connective tissue linking the arms to adjoining ones, indicating that a layer of mutable collagen is present there.

References

External links

* * {{Taxonbar, from=Q3274366 Heliasteridae Animals described in 1816 Marine fauna of South America Taxa named by Jean-Baptiste Lamarck Fauna of the Pacific Ocean