Echinaster

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Echinaster
Zeester.JPG
Echinaster sepositus
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Echinodermata
Class: Asteroidea
Order: Spinulosida
Family: Echinasteridae
Genus: Echinaster
Verrill, 1870 [1]
Species
see text
Synonyms [1]
  • Rhopia Gray, 1840
  • Thyraster Ives, 1890
  • Verrillaster Downey, 1973

Echinaster is a well-studied and common genus of starfish containing ~30 species and is the second-largest genus found within the family Echinasteridae. [2] The genera Henricia and Echinaster encompass 90% of all the species found within the family Echinasteridae. [3] It contains 30 species, however the number of species in this genus is still debatable because of uncertainty within the genera. [3] This genus is currently sub-divided into two sub-genera: Echinaster and Othilia, evolutionary relationships between the sub-genera is not understood. [3] Echinaster are found in the Pacific, Atlantic and Indian oceans, with most species being studied in the Gulf of Mexico and Brazil. [3] The sub-genera Othilia is thought to encompass species mainly found in the Gulf of Mexico and Brazil. [3] Echinaster is often one of the most studied species within the family Echinasteridae and is often used to find evolutionary relationships. [3]

Contents

Many species found within Echinaster are red, orange, or pink in coloration.

Species

Life history

Lifespan

Sea stars can live up to 35 years in the wild under the proper conditions, [5] but the lifespans of Echinaster can be variable and affected by environmental factors such as salinity, temperature of water, light availability, and pollution. [6] Furthermore, the lifespan of an Echinaster can also be affected by humans. Habitat destruction and overfishing are two factors which have adverse affects on populations of Echinaster. [6]

Life cycle

Echinaster are able to start reproduction by broadcast spawning gametes into the water, where externally fertilized eggs develop into planktonic larvae. [6] Most species only produce brachiolaria larvae which are lecithotropic, non-feeding larvae. [6] However, some Echinaster produce larvae which first go through a smaller, feeding bipinnaria stage, and then through the second brachiolaria larval stage. [6] Their eggs vary in size depending on parental investment, the amount of nutrients found in eggs, and the surrounding habitat. [6] Sea stars are deuterostomes and the first cleavage begins shortly after fertilization and is holoblastic. [6] Fourteen hours after fertilization, a wrinkled blastula is formed. [6] Twenty hours after fertilization, a blastula with an invaginated pore at the vegetal pole forms. [6] The blastula then rotates around an axis in circular motions, the embryos then undergo a longitudinal stretching. [6] Cilia begin to surround the entire body causing movement along the anterior-posterior axis. [6] Six days after fertilization occurs, the anterior body extends, while the posterior body flattens laterally. [6] Shortly after, tube feet and the central disk begin to appear on the body. [6] The mouth and spine begin to form on the body and after fifteen days, symmetry is more pronounced and the eyespot has fully developed. [6] 60 days after fertilization occurred the sea stars can evert their stomach, their mouths become active, and they begin to feed on algae. [6] The madreporite develops after 88 days and the hydropore develops on one of the primary plates. [6] The first 40 days of Echinaster's development are distinguished by pronounced growth, after 40 days this growth begins to slow down significantly. [6]

Anatomy

Starfish Anatomy. Elementary zoology (1902) (21233439655).jpg
Starfish Anatomy.

Echinaster generally possess elongated arms attached to a narrow, central disk. [2] They have body wall plates which appear similar to one another and form a meshed support network.[2] These plates contain spinelets, which vary from thorny to cylindrical. [2] The body cavity is composed of three major components: [7] the perivisceral coelom which mainly surrounds the digestive system and the gonads; [7] [8] the perihaemal system, which consists of radial channels and forms a reduced circulatory system; [7] [9] and the water vascular system, which involves hundreds of tube feet, water channels, and the madreporite. [7] Tube feet are involved in processes such as locomotion, adhesion, food collecting and excretion. [7] The madreporite is a small calcified pore that is the location for drawing in and expelling water to fill the water vascular system. [10] The digestive tract contains two stomachs, a large cardiac portion and a smaller pyloric portion. [7] Each digestive gland in the body of Echinaster is connected to the pyloric stomach by the Tiedmann's pouch. [11] Each pouch divides into a series of channels which are lined with cilia and act as a pumping organ for the sea star. [11] In the floor of the Tiedmann's pouch lies the epidermal nerve plexus and the associated spindle nerve cells. [11]

At the end of each arm, the sea star has an optic cushion and ocelli. Echinaster nervous system consists of the ectoneural and the hyponeural systems. [7] Each arm is connected to the circumoral ring and contains a radial nerve cord. [7] [12] The ectoneural system forms two plexus within the body, one epidermal plexus which innervates the body wall and its appendages, and one plexus which innervates the epithelia of each organ. [7]

Arm regeneration

Echinaster sepositus regeneration Echinaster sepositus regeneration.jpg
Echinaster sepositus regeneration

Echinaster can suffer frequent damage to their arms, so it is important they are capable of quick repair. When any part of the arm becomes damaged, the stump of the arm constricts, causing the coelom to seal. [13] The combination of coelomic fluid migrating to the wound site and arm constriction, clots formed and the stump begins to seal, closing any open sites. [13] Papullae appear to deflate and the dense connective tissue becomes more densely packed. [13] Circular muscle fibers contract in the arm causing the tube feet to pull towards the wound. [13] Twenty-four hours into arm regeneration, the body wall of the arm is still contracted and the aboral side of the arm has folded to the oral side. [13] A thin epithelial layer has begun to form and the stump has begun to reform due to dedifferentiated epidermal cells. [13] At this stage, the radial nerve cell has also begun to heal. [13] 72 hours into arm regeneration, the aboral arm wall is still covering the wound site, however, now the body wall has relaxed and the papullae began to inflate again. [13] A new epidermis has formed and is now thicker and stronger than the previous epidermis. [13] Directly beneath the epidermis of the wound, phagocytes can be observed ingesting any bacteria or extra cells which are not necessary for regeneration. [13] Morula cells are also present; these cells focus on wound healing and repairing the extracellular matrix. [13] When the arm is completely repaired, myocytes can be ingested by phagocytes, used a direct source for new cells, or used as a source of energy. [7] Stem cells may also contribute to regeneration in sea stars but little is known about their contributions in the Echinodermata. [7] Altogether, arm regeneration takes a couple of weeks for members of the Echinaster genus, however, the arm begins to repair itself in as few as 3 days. [13]

Locomotion

Echinaster brasiliensis: A-Spines of arm, B-Tube feet, C-Abactinal view of Arm. Echinaster (Othilia) brasiliensis.jpg
Echinaster brasiliensis: A-Spines of arm, B-Tube feet, C-Abactinal view of Arm.

Starfish generally move by using their tube feet. [14] Water enters through the madreporite and reaches the tube feet, causing an expansion and contraction of the tube feet, which moves the sea star. [14] When fully inverted, Echinaster and other sea stars are able to exhibit a behavior known as righting. [15] This response is the ability to adjust tube feet to their proper orientation after a full body inversion. [15] It can be useful if an organism gets caught in a storm surge or is dislodged by a predator, and also serves as a marker to assess their functional status when exposed to environmental changes. [15] As the temperature increases, tube feet can lose their ability to adhere to surfaces. [15] Studies show this is because the neuromuscular system does not adjust to thermal changes well. [15] This directly affects the Echinaster's ability to right, causing their response to be slower and less efficient. [15] When faced with thermal stress, Echinaster were found to right by somersaulting, this is where two adjacent arms twist, with the oral sides facing each other, and touch the substrate to become the sea star's lead arms. [15] Another arm opposite the lead arms then touches the substrate. [15] After this, the lead arms move towards the center of the organism and begin to move under the animal. [15] Finally, the final arm releases the substrate and the free arms flip over the sea star resulting in a somersault motion. [15] Furthermore, not only did a thermal increase result in a change in righting response, it also increased mortality rate in Echinaster and slowed metabolic response rates overall. [15]

Ecology

Habitat

Sea stars of the Echinaster genus are typically found in tropical and temperate waters at the bottom of the sea floor in shallow waters and in rocky shores across the globe. [16] Most of the genus Echinaster can be found within the Caribbean and Mediterranean Seas, Pacific Ocean, Atlantic Ocean, and Indian Ocean. [16] Evidence suggests that some species of these sea stars may linger around mangroves and reefs to prey upon the sponges which populate these areas. [16]

Diet

Echinaster feed mostly on biofilms, encrusting invertebrates, such as sponges, and microalgae. [2] One study performed showed that sea stars of the Echinaster have no problem eating the spicules of sponges, along with the sponge skeleton. [16] Studies also showed that the Echinaster prefer sponge species that lack chemical defenses.[18] They are the least likely to eat sponges with a rubbery texture. [16]

This genera typically associates themselves with their prey in the same area, if not found in a feeding position, their stomachs are typically found partially-everted. [11] When Echinaster settle in feeding positions, their stomachs tend to evert into a button-like structure. [11] Echinaster are able to receive nutrients through external digestive activity or they can acquire nutrients through detritus. [11]

Research

Several species of Echinaster have been studied for potential medical application. One example of this is the Echinaster echinophorus which has been studied for its methanolic extract. [17] The phytochemical analysis showed secondary metabolites including saponins, phenols, tannins, alkaloids, steroids, amino acids and quinones. [17] The extract was tested against mice who were infected with the parasite Leishmania amazonensis, which is known to cause diseases such as leishmaniasis. [17] The study showed that the extract worked against two forms of the parasite and scored a nine on the selectivity index, which indicates the extract is selective against the parasite. [17] The extract reduced the size of lesions, and the amount of parasites without affecting the mice, however it did not cure the mice completely of the parasite. [17] With further studies, this extract could prove to be an effective medicine against leishmaniasis.

Another species within the genera, Echinaster brasiliensis, has been studied to examine the biochemical bases of circadian rhythms, and produces endogenous melatonin in their gonads. [18] This study found that organisms kept in a natural light and dark cycle, where sunrise occurred at 0625 hours and sunset at 1745 hours (6:25 am, 5:45 pm) produced a low concentration of melatonin. [18] There was an increase in melatonin production when sunset was changed to 1700 hours (5 pm) and this was said to last throughout the night. [18] As a control, some organisms were left completely in the dark, these organisms produced about the same amount of melatonin as the natural light organisms. [18] This study demonstrates that there is a nocturnal peak production of melatonin in E. brasiliensis and that melatonin is the result of a biological clock, not light, though it can be a stimulus. [18]

Related Research Articles

<span class="mw-page-title-main">Echinoderm</span> Exclusively marine phylum of animals with generally 5-point radial symmetry

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 7,000 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.

<span class="mw-page-title-main">Starfish</span> Class of echinoderms, marine animal

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.

The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. The system is composed of canals connecting numerous tube feet. Echinoderms move by alternately contracting muscles that force water into the tube feet, causing them to extend and push against the ground, then relaxing to allow the feet to retract.

<span class="mw-page-title-main">Brittle star</span> Echinoderms, closely related to starfish

Brittle stars, serpent stars, or ophiuroids are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomotion. The ophiuroids generally have five long, slender, whip-like arms which may reach up to 60 cm (24 in) in length on the largest specimens.

<span class="mw-page-title-main">Madreporite</span> Opening used to filter water in echinoderms

The madreporite is a light colored calcareous opening used to filter water into the water vascular system of echinoderms. It acts like a pressure-equalizing valve. It is visible as a small red or yellow button-like structure, looking like a small wart, on the aboral surface of the central disk of a sea star or sea urchin or the oral surface of Ophiuroidea. Close up, it is visibly structured, resembling a "madrepore" colony. From this, it derives its name.

<span class="mw-page-title-main">Echinasteridae</span> Family of starfishes

The Echinasteridae are a family of starfish in the monotypic order Spinulosida. The family includes eight genera and about 133 species found on the seabed in various habitats around the world.

<span class="mw-page-title-main">Eleutherozoa</span> Proposed group of marine invertebrates

Eleutherozoa is a proposed subphylum of echinoderms. They are mobile animals with the mouth directed towards the substrate. They usually have a madreporite, tube feet, and moveable spines of some sort, and some have Tiedemann's bodies on the ring canal. All living echinoderms except Crinozoa and Blastozoa belong here.

<i>Linckia guildingi</i> Species of starfish

Linckia guildingi, also called the common comet star, Guilding's sea star or the green Linckia, is a species of sea star reported from the shallow waters of the tropical Pacific Ocean, Indian Ocean, Atlantic Ocean and the Caribbean Sea.

<i>Pisaster brevispinus</i> Species of starfish

Pisaster brevispinus, commonly called the pink sea star, giant pink sea star, or short-spined sea star, is a species of sea star in the northeast Pacific Ocean. It was first described to science by William Stimson in 1857. The type specimen was collected on a sandy bottom, 10 fathoms (18 m) deep, near the mouth of San Francisco Bay.

<span class="mw-page-title-main">Asterozoa</span> Phylum of marine invertebrates

The Asterozoa are a subphylum in the phylum Echinodermata. Characteristics include a star-shaped body and radially divergent axes of symmetry. The subphylum includes the class Asteroidea, the class Ophiuroidea, and the extinct order Somasteroidea.

<i>Stichaster australis</i> Species of starfish

Stichaster australis, the reef starfish, is a species of starfish found in the shallow waters of the rocky intertidal of New Zealand. Typically, the animal is endemic to the west coast shores of the North and South Islands, where wave action is increased. They do not usually inhabit ecosystems that have reduced wave action and calm conditions as they prefer a higher-energy environment. These marine invertebrates range in color from pink to purple, but can also be orange. They typically have eleven arms, but sometimes they may have either ten or twelve. As full-grown adults, they are 8 to 10 cm in diameter.

Asexual reproduction in starfish takes place by fission or through autotomy of arms. In fission, the central disc breaks into two pieces and each portion then regenerates the missing parts. In autotomy, an arm is shed with part of the central disc attached, which continues to live independently as a "comet", eventually growing a new set of arms. Although almost all sea stars can regenerate their limbs, only a select few sea star species are able to reproduce in these ways.

<i>Asterias forbesi</i> Species of starfish

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.

<i>Pteraster tesselatus</i> Species of starfish

Pteraster tesselatus, the slime star or cushion star, is a species of starfish in the family Pterasteridae found in the North Pacific.

<span class="mw-page-title-main">Orange knobby star</span> Species of starfish

The orange knobby star, Echinaster echinophorus, is a species of sea star found in the Caribbean Sea and along the Atlantic coast of South America.

<i>Echinaster spinulosus</i> Species of starfish

Echinaster spinulosus, the small spine sea star, is a species of sea star found in shallow parts of the western Atlantic Ocean, the Caribbean Sea and Gulf of Mexico.

<i>Henricia sanguinolenta</i> Species of starfish

Henricia sanguinolenta, commonly known as the northern henricia, is a species of sea star from the North Atlantic and North Pacific oceans. Henricia sanguinolenta is very similar to Henricia oculata, also known as "bloody Henry", and the two can only be distinguished by laboratory tests. It comes in colors of red, yellow, orange, purple, and lavender.

<i>Luidia magellanica</i> Species of starfish

Luidia magellanica is a species of starfish in the family Luidiidae. It is found in the southeastern Pacific Ocean on the coast of South America.

<i>Echinaster luzonicus</i> Species of starfish

Echinaster luzonicus, the Luzon sea star, is a species of starfish in the family Echinasteridae, found in shallow parts of the western Indo-Pacific region. It sometimes lives symbiotically with a copepod or a comb jelly, and is prone to shed its arms, which then regenerate into new individuals.

<span class="mw-page-title-main">Starfish regeneration</span> Star-shaped organisms

Starfish, or sea stars, are radially symmetrical, star-shaped organisms of the phylum Echinodermata and the class Asteroidea. Aside from their distinguished shape, starfish are most recognized for their remarkable ability to regenerate, or regrow, arms and, in some cases, entire bodies. While most species require the central body to be intact in order to regenerate arms, a few tropical species can grow an entirely new starfish from just a portion of a severed limb. Starfish regeneration across species follows a common three-phase model and can take up to a year or longer to complete. Though regeneration is used to recover limbs eaten or removed by predators, starfish are also capable of autotomizing and regenerating limbs to evade predators and reproduce.

References

  1. 1 2 Mah, C., Hansson, H. (2013). Mah CL (ed.). "Echinaster Müller & Troschel, 1840". World Asteroidea database. World Register of Marine Species . Retrieved 2013-11-13.
  2. 1 2 3 4 Mah, Christopher L.; Blake, Daniel B. (2012-04-27). "Global Diversity and Phylogeny of the Asteroidea (Echinodermata)". PLOS ONE. 7 (4): e35644. Bibcode:2012PLoSO...735644M. doi: 10.1371/journal.pone.0035644 . ISSN   1932-6203. PMC   3338738 . PMID   22563389.
  3. 1 2 3 4 5 6 Seixas, Victor Corrêa; Ventura, Carlos Renato Rezende; Paiva, Paulo Cesar (2018-01-16). "The complete mitochondrial genome of the sea star Echinaster (Othilia) brasiliensis (Asteroidea: Echinasteridae)". Conservation Genetics Resources. 11 (2): 151–155. doi:10.1007/s12686-018-0986-3. ISSN   1877-7252. S2CID   32685575.
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  5. ↑ "Starfish (Sea Stars) | National Geographic". Animals. 2010-09-10. Retrieved 2020-04-06.
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  8. ↑ "Perivisceral coelom | zoology". Encyclopedia Britannica. Retrieved 2020-04-14.
  9. ↑ "Perihaemal | Definition of Perihaemal by Lexico". Lexico Dictionaries | English. Retrieved 2020-04-14.[ dead link ]
  10. ↑ FERGUSON, JOHN C. (1984). "Translocative Functions of the Enigmatic Organs of Starfish—The Axial Organ, Hemal Vessels, Tiedemann's Bodies, and Rectal Caeca: An Autoradiographic Study". The Biological Bulletin. 166 (1): 140–155. doi:10.2307/1541437. ISSN   0006-3185. JSTOR   1541437.
  11. 1 2 3 4 5 6 FERGUSON, JOHN CARRUTHERS (1969). "Feeding Activity Inechinasterand ITS Induction with Dissolved Nutrients". The Biological Bulletin. 136 (3): 374–384. doi:10.2307/1539682. ISSN   0006-3185. JSTOR   1539682.
  12. ↑ "Medical Definition of CIRCUMORAL". www.merriam-webster.com. Retrieved 2020-04-14.
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  14. 1 2 Sharma, Bhoomika (2020-02-09). "How Does A Starfish Move? » Science ABC". Science ABC. Retrieved 2020-04-14.
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  16. 1 2 3 4 5 Waddell, B; Pawlik, JR (2000). "Defenses of Caribbean sponges against invertebrate predators. II. Assays with sea stars". Marine Ecology Progress Series. 195: 133–144. Bibcode:2000MEPS..195..133W. doi: 10.3354/meps195133 . ISSN   0171-8630.
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  18. 1 2 3 4 5 Peres, Rafael; Amaral, Fernanda Gaspardo; Marques, Antonio Carlos; Neto, José Cipolla (2014). "Melatonin Production in the Sea Star Echinaster brasiliensis (Echinodermata)". The Biological Bulletin. 226 (2): 146–151. doi:10.1086/bblv226n2p146. ISSN   0006-3185. PMID   24797096. S2CID   44882942.
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