Aphelasterias japonica
From Wikipedia, the free encyclopedia
| Aphelasterias japonica | |
|---|---|
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| An Aphelasterias japonica | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | Asteroidea |
| Order: | Forcipulatida |
| Family: | Asteriidae |
| Genus: | Aphelasterias |
| Species: | A. japonica |
| Binomial name | |
| Aphelasterias japonica (Bell, 1881) | |
“Aphelasterias japonica” (A. japonica) is a species of sea star in the family Asteriidae that is native to the northwestern Pacific Ocean. It is found in coastal marine environments in Japan and surrounding regions, where it acts as a benthic predator and is associated with a variety of substrates and habitats.[1]
The species has been studied for its reproductive biology, immune system, and production of bioactive compounds.
Aphelasterias japonica was first described by Francis Jeffrey Bell in 1881. It belongs to the phylum Echinodermata and class Asteroidea, which includes sea stars. The species is classified within the order Forcipulatida and the family Asteriidae, which are a group of predatory sea stars that are in marine environments all over the world.
Taxonomic databases recognize A. japonica as a valid species, with synonyms including ''Asterias japonica'' and ''Asterias torquata''.[2][3]
Description
Aphelasterias japonica is a medium sized sea star that has five elongated arms extending from a small central disc. Individuals can reach approximately 20-30 cm in diameter.[4] The aboral (upper) surface is reddish to pink, while the oral surface is lighter in color.
The body surface contains small spines and pedicellariae, which are structures found in sea stars and are used for protection and cleaning the body surface. It uses tube feet (podia), located along ambulacral grooves, for movement and feeding.[4]
Distribution and habitat
Aphelasterias japonica is native to the northwestern Pacific Ocean and has been recorded along the coastal waters of Japan and the Russian Far East.[4] It occurs across a broad range, from intertidal and subtidal zones to depths of approximately 100m, but is most found around 20-25 meters.[4]
The species inhabits a wide range of habitats, including rocky, sandy and muddy substrates, as well as gravel beds. It is also found in more complex habitats like kelp forests, coralline algae beds, and shellfish reefs.[4]
Because it is often found in highly productive habitats (kelp forests and shellfish beds) its distribution is likely influenced by the availability of prey organisms.[4][5]
Ecology and behavior
Aphelasterias japonica is a mobile benthic predator that feeds mainly on small, slow-moving invertebrates, especially bivalve mollusks.[4] Like other sea stars, it captures prey using its tube feet and digests food externally by everting its cardiac stomach. This allows it to break down and consume organisms with hard shells that would otherwise be difficult to eat.[4]
The ability of A. japonica to move through different substrates allows it to take advantage of patchy food resources and find a variety of prey species.[4] It contributes to trophic interactions between predator and prey populations within its coastal marine ecosystems.[4]
In addition to direct predation, A. japonica produces bioactive chemical compounds known as asterosaponins, which function as part of its chemical defense system.[5] These compounds have been shown to cause toxic effects on marine organisms under experimental conditions, including embryotoxic and cardiotoxic effects in fish models.[5]
These results suggest that the ecological impact of A. japonica is not only based on its feeding behavior. Its chemical defenses may also influence how it interacts with other organisms and its surrounding environment. Outbreaks of sea stars with strong chemical and physical defenses have been associated with disruptions in marine ecosystems and economic losses in aquaculture systems.[5]
In areas with high densities of shellfish, A. japonica has been associated with damage to aquaculture operations through both direct predation and the chemicals they produce.[4][5] The combined effects of predation and defenses shows how A. japonica affects the benthic communities in the intertidal and subtidal zones where it is found.
Reproduction and development
Reproduction in A. japonica occurs through broadcast spawning, where gametes are released into the water column and fertilization occurs externally. Spawning is seasonal and has been recorded from late summer through autumn in different parts of its range.[4]
At the molecular level, reproduction is regulated by hormonal signaling pathways. A relaxin-like gonad-stimulating peptide (RGP) acts as a gonadotropin and stimulates ovarian tissue to produce 1-methyladenine, which induces oocyte maturation and ovulation.[6][7] The role of 1-methyladenine as a maturation-inducing hormone has been well established in starfish.[8]
After fertilization, embryos develop into gastrulae and then into planktonic bipinnaria larvae,[8] which represent the primary feeding stage. These larvae use ciliary bands for movement and feeding on suspended particles in the water column. In many sea stars, this stage is followed by a brachiolaria larva before settlement and metamorphosis into the juvenile form.[8][9]
Experimental studies have investigated early developmental processes in laboratory conditions, which provide insight into cellular control mechanisms during development.[9]
Physiology and cell biology
The coelomic fluid of A. japonica contains coelomocytes, which play an important role in immune defense and wound response.[10] These cells show a wide range of morphologies, including amoeboid and irregular forms that are associated with phagocytic activity, meaning they help break down cellular debris or foreign material, and help with wound healing.[11][10] These processes are necessary for maintaining homeostasis.
Quantitative analyses using morphometric and fractal approaches have identified multiple coelomocyte types based on characteristics such as size, symmetry, and spatial complexity.[12] These differences are interpreted as reflecting functional variation, including roles in pathogen recognition and removal of cellular debris.[10] Meaning that coelomocytes play an important role in maintaining homeostasis and responding to environmental stress.