SEA STAR SPECIES
Starfish are also known as asteroids because they belong to the class Asteroidea. They are ectothermic (use heat from the environment and adapt their behavior to regulate body temperature), heterothermic (have a body temperature that fluctuates with the surrounding environment) and have radial symmetry (symmetry around a central axis). There are about 1,900 species of starfish. They live exclusively on ocean floor and can be found in all the world's oceans — from warm, tropical waters to frigid, polar seas, and from from shallow intertidal zones down to abyssal depths of over 6,000 meters (20,000 feet) below the surface. [Source: Wikipedia]
Sea stars in the genus Pisaster are a keystone predators in the rocky intertidal zone off the Pacific Coast. They maintain diversity in tidal regions by keeping the strongly competitive bivalves at a low enough population level that they could not monopolize all the resources and form a monoculture. [Source: Kim Chau, Animal Diversity Web (ADW)]
Sunflower stars can reach two feet across and have more than 40 arms. Not only is it one of the largest starfish it is also quite fast, reaching speeds of one and half meters (five feet) a minute using 15,000 tube feet. Tube feet also help sea stars hold their prey. See Separate Article on these guys.
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures; Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) coris.noaa.gov ; International Coral Reef Initiative icriforum.org ; Coral Reef Alliance coral.org ; Global Coral reef Alliance globalcoral.org ; Global Coral Reef Monitoring Network gcrmn.net
Common sunstar (Scientific name: Crossaster papposus) belong to the family Solasteridae and native to colder water of the northern Atlantic and the Pacific Oceans. It is distributed from the Arctic down to the English Channel, in the North Sea in the Atlantic and from Alaska to Puget Sound near Seattle in the Pacific. They have also been observed off of Iceland and Greenland and in the Barents Sea, Kola Bay, Okhotsk Sea and the White Sea around Russia. The common sunstar is commonly found on rocky bottoms, coarse sand and gravel, preferably in moving water, from the low-tide line to depths of 300 meters (1,000 feet). [Source: Wikipedia]
Common sunstars are reddish on top with concentric bands of white, pink, yellow, or dark red, and it is white on their underside. They are covered on top with brushlike spines. Their thick, central disc is fairly large and has a netlike pattern of raised ridges. The mouth area is bare. The arms are relatively short and usually number eight to fourteen. Their diameter can be up to 30 centimeters (one foot). The madreporite plate stands out clearly. Common sunstar are omnivores. They eat almost anything including smaller starfish and sunstars, swallowing them whole.
Common Stafish (Scientific name:Asterias rubens) are native to the northern Atlantic Ocean. They favor sandy and rocky, temperate shores and live in a variety of depths, from shallow shores water to depths to up to 366 meters (1,200 feet). Studies in coastal Nova Scotia found these starfish lived in kelp beds and were the only echinoderms found on the kelp fronds. Other studies have shown that population densities of common starfish are correlated with the prevalence of subtidal blue mussel (Mytilus edulis), beds. These mussel beds are often short-lived due to intense predation of common starfish.[Source: Cheryl Lewis, Animal Diversity Web (ADW) /=]
The body of the common starfish consists of a central disk from which five arms radiate outward. The arms are not sharply marked off from the central disk. There is no defined head. The mouth is in the center of the disk on the underside of the sea star. Common starfish come in variety of colors including red, orange and purple. Their arm length diameter can measure anywhere from five millimeters to 15 centimeters (six inches). Common starfish are not endangered. They have no special status according to the Convention on the International Trade in Endangered Species (CITES) and the International Union for Conservation of Nature (IUCN) Red List.
The breeding season for common starfish is in the spring. They reach sexual maturity at about one year of age. Sea stars may reproduce sexually and asexually. Asexual reproduction involves division of the disk and regeneration of each half. Sexual reproduction involves the production of sperm and eggs by separate female and male sea stars. Fertilization occurs outside the individuals in the seawater. During embryo development, common starfish form into blastulas, which form into larva — with structures such as a gut, anus, and coelom — in three days
Populations of Common starfish have been found to be infected with the ciliate Orchitophrya stellarum, a parasite that infects only male sea stars and causes a variety of damage, including mechanical damage to the gonads, alteration in the host's hormonal pattern, and direct consumption of gonadal tissues. This decreases the reproductive potential of a population and may reduce the proportion of males to females. Fortunately, the decline in the number of males within a population, increases the likelihood of larvae survivorship because of increased food availability.
Common Starfish Locomotion and Feeding
Common starfish have a water vascular system, characteristic of all echinoderms, which is used for locomotion and other things. The underside of the starfish is covered with hundreds of tube feet used for walking, attaching to rocks, and holding on to prey. Common starfish have been timed at speeds of 30 centimeters (one foot) per minute, or 18 meters (60 feet) per hour. The suction cups on the end of the tube feet are used for grasping and eating prey and climbing up surfaces. [Source: Cheryl Lewis, Animal Diversity Web (ADW) /=]
According to Animal Diversity Web: Common starfish feed mainly upon molluscs, especially bivalves and snails. In addition, they act as scavengers on any dead animals they encounter. Like all sea stars, the stomach of common starfish turns inside out through the mouth and slips into the shell of the prey. Next, digestive enzymes enter the prey along with the everted stomach lining to further aid in digestion. The sea star also may use its tube feet to pry open a bivalve. /=\
Studies have monitored the predation of common starfish upon sea scallops. The experiments were designed to test the importance of prey size and vulnerability of the sea scallops to the sea stars. Common starfish preferred small- to medium-sized scallops, based on the sea star's ability to slowly sneak upon the prey. When doing so, predatory sea stars emit saponins to which scallops and other prey species detect and use against the predator to monitor the distance between the two. This allows the scallop time to protect itself from the hungry predator by assuming the ready-to-swim position. Crabs and other fish have the advantage of agility compared to the slow creeping sea stars, allowing these quicker organisms better food selection, or in other words, larger scallops.
Forbes’ Sea Star
Forbes’ sea stars (Scientific name:Asterias forbesi) are also known as common sea stars. They look similar to common starfish and are one of the most common starfish species on the North American Atlantic coast. They are commonly found in intertidal areas and shallow waters. Sometimes they are found in great numbers but they don't form colonies. They favor rocks, boulders, and oyster, clam, scallop, mussel beds. Rocks are important to help prevent them from being washed away by currents and waves. Bivalve beds are sources of plentiful food within range.[Source: Kim Chau, Animal Diversity Web (ADW) /=]
Forbes’ sea stars population are thriving. The have no special status on the International Union for Conservation of Nature (IUCN) Red List. They are regarded by some as pests. They can get into mollusk beds and consumer animals farmers and fishermen for hoping to harvest for human food.
Most Forbes’ sea stars range in size from 7 to 15 centimeters (three to six inches) in diameter. They are tan, brown, or olive with tomes of orange, red, or pink. Their spines are large in diameter and are a distinguishing feature of this species. The spines are surrounded at their base by pedicellariae which are little jaws that keep the body free of debris and maybe catch a little food, too. There are little tufts of skin on the surface that serve as gills. The madreporite (the perforated plate by which seawater enters the sea star’s vascular system) is pink.
Forbes’ sea stars feeds chiefly on bivalve molluscs. They grasp clams, mussels and clams with their tube feet and use suction and muscle strength to pull the shells apart enough to extend their stomachs out through their mouth into the mollusk. Forbes’ sea stars can move at a rate of 15-20 centimeters per minute in unthreatened ocean water, but when under attack, can speed up to 25-35 centimeters per minute.
Common comet stars (Scientific name: Linckia guildingii) are found in the western Atlantic Ocean from Florida to Brazil, and around the Caribbean islands — and in Australia at the Great Barrier Reef. Also known as Guilding's sea stars or green Linckia, they primarily live on hard, flat bottoms of coral reefs, but may also be found on slopes and sandy regions, at depths of one to 100 meters (3.28 to 328 feet). They typically inhabit shallow depths are are usually it is hidden, but are sometimes exposed. Common comet stars and comet stars (Ophidiaster guildingii) are two similar species that are often confused due to their shape, coloration and where they live. Comet stars, however, have arms of equal length. They also have 15 pores per papular area, and Common comet stars can have up to 30.[Source: Adrianne Stropes, Animal Diversity Web (ADW) /=]
Common comet stars reach lengths of 22 centimeters (8.66 inches). They have four to seven cylindrical arms of uneven length. Their comet shape — a star with a long tail — is caused by its asexual mode of reproduction. The longest arm came from the parent, while the "star" is composed of smaller, regenerated arms.
These sea stars be more symmetrically shaped at different stages of their life. Coloration changes with age. Adults are usually uniformly gray in color but reddish brown, yellowish brown, tan, or violet ones have been observed. Juveniles tned to be mottled white, gray, purple, violet, red or brown. /=\
Common comet stars are both motile (move around as opposed to being stationary) and , sedentary (remain in the same area), They to stay hidden to avoid predation by fish and come out and move around to feed. According to Animal Diversity Web: Some food may be gathered from dead fish. However, the primary food source is from benthic (bottom-dwelling) felt (made up of protozoans, algae, and bacteria). Hard surfaces like coral-rock and sand are covered with a layer of this organic material. Common comet stars was proposed to be a filter (ciliary) feeder, and are generally thought to be a detritivores (mainly eat decomposed plants and/or animals, in this case, felt). Common comet stars have a smaller cardiac stomach (large oral chamber) and larger rectal caeca (small outpocketings in in the intestine) when compared with other species.
Comet Star Reproduction
Common comet stars employ both sexual and asexual reproduction. They are oviparous (young are hatched from eggs) and engage in seasonal breeding. Reproduction is external, meaning the male’s sperm fertilizes the female’s egg outside her body. There is no parental involvement in the raising of offspring. [Source: Adrianne Stropes, Animal Diversity Web (ADW) /=]
According to Animal Diversity Web: Asexual reproduction is the dominant form. Arms voluntarily detach to form a new individual (known as autotomy). The new "daughter" has an identical genetic makeup to the parent. In sexual reproduction, the sexes are separate. The females release many eggs. They are colorless and about 0.1 millimeters in diameter. The eggs are negatively buoyant upon leaving the female's gonopores (found on the arms). The development of larva is planktotrophic, meaning the larvae primarily survives by feeding on plankton. /=\
Males have serially arranged gonads, with each arm containing several gonoducts. The gonads are particularly dominant before they spawn. At this time, gametes are released in the water, resulting in external fertilization. Some research has been done on the effect of the hormone 1-methyl adenine. When injected with the hormone, the starfish released their gametes, usually within three hours. The results varied depending on proximity to the natural mating season. For Common comet stars, the peak was in mid-summer in Australia (December).
Cushioned Sea Stars
Cushion sea stars (Scientific name: Oreaster reticulatus) range from around South Carolina to the Caribbean Islands in the western Atlantic Ocean, and is most common in shallow waters in the Carribean. Also known as cushion stars, they have been introduced to the Cape Verde Islands in Western Africa. Cushion sea stars prefer calm, shallow, subtropical and tropical water at depths of one to 37 meters (3.28 to 121.39 feet). They are found in the greatest numbers on coarse, calcereous sandy bottoms that are isolated or surrounded by seagrass. They can also be found in soft sand and mud substrates associated with shallow reefs, mangroves, or lagoons. [Source: Rachel Miranda and Shital Patel, Animal Diversity Web (ADW) /=]
Cushion sea stars are large. The only recorded predators of adult cushion sea stars are the triton Charonia variegata, a gastropod. Juvenile Cushion sea stars are green, which provides camouflage. The cushion sea star's daily activities coincide with the changes in light intensity, usually around dusk and dawn. This allows them to avoid predators and arrange foraging activity with the activity of their prey. Through feeding, cushion sea stars can turn over sediment at a rate of 1.9 times in a 24-hour period.
Cushion sea stars are omnivores (eats a variety of things, including plants and animals), and also a deposit feeder. They feed on sea urchins, juveniles sea cucumbers , and other invertebrates including polychaete worms, copepods, ostracods, crab larvae and sponge tissue. The sea star piles sediments and everts its large cardiac stomach, which allows it to surround prey. food. Digestive juices are then excreted to break down the food.
Cushion stars have not been evaluated for the International Union for Conservation of Nature (IUCN) Red List. They have no special status according to the Convention on the International Trade in Endangered Species (CITES) but are protected in the Carribean because of over-exploitation by souvenir hunters there ,
Cushioned Sea Stars Characteristics, Behavior and Mating
Cushion sea stars range in length from 20 to 50 centimeters (0.66 to 1.64 feet). Their lifespan depends on food availability. If there is low food availability, the cushion star will re-absorb its own tissue, which leads to a reduction in size. Cushion sea stars have a central disc from which its five tapered arms radiate. Their body is covered by a hard outer shell with knobby spines, or ossicles, that extend away from the surface. They can be easily distinguished from closely related species by their hard shell and short tapered arms. Individuals vary in color and can be brown, red, orange, or yellow. [Source: Rachel Miranda and Shital Patel, Animal Diversity Web (ADW) /=]
Cushion sea stars are diurnal (active mainly during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area) and solitary. They move around slowly using their tube feet at speeds of approximately 12 to 33 centimeters (5 to 13 inches) per minute.
Cushion sea stars sense using vision, touch, vibrations and chemicals usually detected with smel and communicate with touch and chemicals usually detected by smelling, and vibrations. They recognize when a potential mate is in close proximity. To increase chances of fertilization, individuals aggregate when ready to spawn. These events rely on environmental cues, such as the length of daylight.
Cushion sea stars are oviparous (young are hatched from eggs) and engage in external reproduction in which sperm from the male fertilizes the female’s egg outside her body. They employ broadcast (group) spawning, the main mode of reproduction in the sea. It involves the release of both eggs and sperm into the water and contact between sperm and egg and fertilization occur externally. Cushion stars are polygynandrous (promiscuous), with both males and females having multiple partners. They reproduce when there are dense aggregations, up to 14 per square meter. Sperm and eggs are released when male and female sea star are in close proximity. Having large numbers of males and females ensures eggs will be fertilized.
Cushioned star spawns engage in seasonal and year-round breeding. In subtropical areas, they reproduces synchronously during the summer. In warmer areas, asynchronous spawning can occur year round. Parental care is minimal. The planktonic larvae are dispersed over long distances and feed on their own. Cushion sea star ags are large and buoyant and drift in ocean currents. By the time the planktonic larvae have developed completely they have lost their bouyancy. They settle on the ocean floor and metamorphose in seagrass beds within 23 days at 23 degrees C. Sexual maturity is reached at a radius of 12 centimeters (five inches). During the last juvenile stage they measure 6 to 12 centimeters (2.3 to 5 inches) in length. /=\
Sea Stars 6,000 Meters Deep in the Marianas Trench
Brisingid sea stars lives exclusively in the deep-sea at depths to 6,000 meters (19,685 feet). They extend their arms up into the water column to capture food and have spines covered by pedicellariae (small wrench- or claw-shaped appendages). Novodinia, have been observed sitting on a dead bamboo coral branch and feeding on crustaceans being carried by in the current [Source: Chris Mah - Smithsonian Institution’s National Museum of Natural History, June 24, 2016]
Deep-sea stars in the genus Coronaster have many ed starfish and a flexible body that has been seen of folded back onto itself into crack on the deep-sea floor. The weird red jumble first videoed was so “un-starfish like” that scientists were uncertain what it was at first! All of the round structures on the surface were spines. Each one carries a big ball of bear trap-like claws called pedicellariae which can be used to defend the organism or to feed on prey. Most times these animals have been observed they have been splayed out on the ocean floor. When tucked into a crevice in defense the animal has its main disk and arms tucked away with its spines facing outwards.
The deep-sea asteroid called Cheiraster sp. (in the family Benthopectinidae) as a large round ball-shaped bulge on the arm is actually an extension from the INSIDE of the body because the sea star has been infected by what is most likely a parasitic barnacle. Chris Mah of the Smithsonian wrote in : These barnacles are different from the ones that most people encounter. They lack the familiar external plates and are instead very soft-bodied. Their larvae enter into the starfish body cavity and begin to grow, taking advantage of the host animal’s nutrients and sometimes their reproductive systems. The parasites can produce thousands of eggs, likely generated at the expense of the host.
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated May 2023