| Astropecten articulatus | |
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| Astropecten articulatus on the beach | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | Asteroidea |
| Order: | Paxillosida |
| Family: | Astropectinidae |
| Genus: | Astropecten |
| Species: | A. articulatus |
| Binomial name | |
| Astropecten articulatus (Say, 1825) | |
| Synonyms [1] | |
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The Astropecten articulatus, more commonly known as the Royal Starfish, is a West Atlantic sea star of the family Astropectinidae. [1]
The Royal Starfish is characterized by its bold colors. It has a purple granulated disk, which is the central region of the sea star, and the purple color continues to extend to its five arms. The margin of the sea star, which is its outline, is an orange color. Entomologist Thomas Say describes the sea star's margin as “articulated throughout”, [2] meaning that the orange margin that surrounds the sea star is continuous, even at the joints of its rays. It also has white spines that are attached to the orange margin and tube feet at the ends of its rays.
The tube feet are cylindrical with conical ends, and the epithelium of the tube foot is covered by a thin layer of cuticle. Underneath the epithelium is the nervous tissue, and underneath that are fibrous tissues in the form of both left and right helices which protect the sea star's muscle tissue layer. The tube feet also contain bilobed ampulla. The ampulla muscle layers in the tube feet allow for the tube feet to elongate and shorten, which allows the sea star to move. [3]
Morphologically, the Royal Starfish is very similar to the Red Comb Starfish. In the past, it was thought that a difference between the two species was that the Red Comb Starfish has needle-like granules in its disk while the Red Comb Starfish has spherical ones. [2] However, a newer study has found that the granules are not spherical, and may have the appearance of that shape due to folding [3]
The sea star can be found on the east coast of the continental Americas, particularly in the Caribbean.
The Royal Starfish feeds by swallowing its food whole and digesting it in its stomach, like other members of the genus Astropecten. However, unlike other species in the same genus, it consumes significantly more organisms. In a study investigating the stomach contents of 124 Royal Starfishes, scientists found that on average, each sea star has 12 organisms in its stomach, with the highest number of organisms recorded being 54. [4] When comparing the number of organisms in the Royal Starfishes' stomachs to another study investigating the stomach contents of the Red Comb Starfish, it is revealed that the Royal Starfishes have much higher amounts. Also, one study investigating A. irregularis shows the same outcome, that there are more organisms in the stomachs of Royal Starfishes than A. irregularis, but in another study, the stomachs of both sea star species are relatively the same.
Royal Starfishes also feed on a diverse number of organisms. From the previous study, in all of the 124 sea stars combined, there were a total of 91 species of organisms found in their stomachs. The three most abundant species were A. candy, N. pusila, and O. music, which were gastropods, and accounted for 60% of all species that Royal Starfishes feed on. [4] The study also found that the sea star consumes the mollusk shell regardless of whether or not the original organism is still inside. The fact that the scientists found parts of Royal Starfishes in their stomachs means that they can be considered cannibals, which is also the case for their relative A. irregularis.
An investigation of three digestive enzymes in the stomachs of Royal Starfishes gives more information about its feeding. The study measured enzyme activity of the enzymes chymotrypsin, -glucosidase, and -glucosidase on subtropical and polar echinoderms. Regarding Royal Starfishes, the study showed that it had very low levels of -glucosidase, but high levels of -glucosidase, and average levels of chymotrypsin. [5] Since -glucosidase involves the degradation of detritus, it is bizarre that the sea star has relatively low levels of it because it contradicts the findings of Wells’ study: that the sea star consumes the shell of any mollusk regardless of whether or not there is an organism inside. Also, the high levels of -glucosidase indicate that the sea star also consumes high levels of plants, since that enzyme involves the degradation of plants. Lastly, even though Wells’ study found that the sea star consumes more organisms than other species of the same genus and is highly carnivorous, it is surprising that it does not have as high chymotrypsin levels as others. Chymotrypsin is involved in the degradation of proteins, so an organism that consumes more protein should have higher levels, but that is not the case with Royal Starfishes.
When investigating the foraging patterns of Royal Starfishes, a Royal Starfish was given two choices of equal amounts of organisms to consume: either low-quality or high-quality. The Royal Starfish chose to consume the higher quality organism more often than the low-quality one. [6] In the same study, it was also given a choice of small-sized prey and larger-sized prey. The Royal Starfish chose to consume the smaller-sized prey more often, and this is because smaller prey decreases handling time. This means that the sea star prefers to consume the organism that would provide it with the most net energy gain for the shortest time, and therefore forages optimally.
The scientists also found that Royal Starfishes exhibit directional movement when prey are not present in their surroundings. However, when prey is present, they start to exhibit more change in movement and speed. [6] This means that when prey is present, they alter their movement patterns so that they forage in areas with “higher prey density”, which is more evidence of the sea star foraging optimally. Lastly, the study found that the sea star forages twice a day, at dawn and dusk, which is similar to other species in the Astropecten genus.
Overall, the feeding patterns of Royal Starfishes can be summarized as foraging optimally on mollusks and possibly plants, but also consuming more organisms than the typical starfish species.
An echinoderm is any deuterostomal animal of the phylum Echinodermata, which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larvae, as adults echinoderms are recognisable by their usually five-pointed radial symmetry, and are found on the sea bed at every ocean depth from the intertidal zone to the abyssal zone. The phylum contains about 7,600 living species, making it the second-largest group of deuterostomes after the chordates, as well as the largest marine-only phylum. The first definitive echinoderms appeared near the start of the Cambrian.
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 are also known as asteroids due to being in the class Asteroidea. About 1,900 species of starfish live on the seabed in all the world's oceans, from warm, tropical zones to frigid, polar regions. They are found from the intertidal zone down to abyssal depths, at 6,000 m (20,000 ft) below the surface.
A molluscivore is a carnivorous animal that specialises in feeding on molluscs such as gastropods, bivalves, brachiopods and cephalopods. Known molluscivores include numerous predatory molluscs,, arthropods such as crabs and firefly larvae, and, vertebrates such as fish, birds and mammals. Molluscivory is performed in a variety ways with some animals highly adapted to this method of feeding behaviour. A similar behaviour, durophagy, describes the feeding of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled molluscs, or crabs.
Astropecten is a genus of sea stars of the family Astropectinidae.
Astropecten polyacanthus, the sand sifting starfish or comb sea star, is a sea star of the family Astropectinidae. It is the most widespread species in the genus Astropecten, found throughout the Indo-Pacific region. The armspread is up to 20 cm (8 in). The specific epithet "polyacanthus" comes from the Latin meaning "many thorned".
Astropecten aranciacus, the red comb star, is a sea star of the family Astropectinidae. It is native to the east Atlantic Ocean and the Mediterranean Sea.
The Paxillosida are a large order of sea stars.
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 indicator for the health of the intertidal zone.
Luidia ciliaris, the seven-armed sea star, is a species of sea star (starfish) in the family Luidiidae. It is found in the eastern Atlantic Ocean and the Mediterranean Sea.
Astropecten irregularis is a sea star of the family Astropectinidae. Common names include Sand sea star.
Luidia clathrata is a tropical species of starfish in the family Luidiidae. It is variously known as the slender-armed starfish, the gray sea star, or the lined sea star. It is found in the western Atlantic Ocean.
Archaster typicus is a species of starfish in the family Archasteridae. It is commonly known as the sand star or the sand sifting star but these names are also applied to starfish in the genus Astropecten. It is found in shallow waters in the Indo-Pacific region.
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.
Evasterias troschelii is a species of starfish in the family Asteriidae. Its common names include the mottled star, false ochre sea star and Troschel's true star. It is found in Kamchatka and the north western coast of North America.
Luidia senegalensis, the nine-armed sea star, is a tropical species of starfish in the family Luidiidae found in the western Atlantic Ocean.
Luidia foliolata, the sand star, is a species of starfish in the family Luidiidae found in the northeastern Pacific Ocean on sandy and muddy seabeds at depths to about 600 m (2,000 ft).
The spiny sand seastar is a species of starfish in the family Luidiidae. It is found in shallow parts of the China Sea and in the vicinity of the Korean archipelago. The tissues of this starfish have been found to contain several secondary metabolites with medicinal potential.
Astropecten armatus, the spiny sand star or Estrella de Arena, is a sea star in the family Astropectinidae. It is found on sandy or gravelly areas in the East Pacific ranging from California (USA) to Ecuador.
Luidia savignyi is a species of starfish belonging to the family Luidiidae. The species is found in the tropical and subtropical Indo-Pacific region. It is a large starfish and preys on other echinoderms.
Rathbunaster is a monospecific genus of sea stars in the family Asteriidae. The genus name was given by Walter Kenrick Fisher to honor the starfish biologist Richard Rathbun of the Smithsonian Institution. He originally ranged this genus under the family Pycnopididae, synonymous with Asteriidae.
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