| Leptasterias hexactis | |
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| Leptasterias hexactis | |
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| Species: | L. hexactis |
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| Leptasterias hexactis | |
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Leptasterias hexactis is a species of starfish in the family Asteriidae, commonly known as the six-rayed star. It is found in the intertidal zone of the western seaboard of the United States. It is a predator and is unusual among starfish in that it broods its eggs and young.
Leptasterias hexactis forms part of a species complex. Over the years, various authorities have discussed the phylogenetic relationships of L. epichlora, L. aequalis and L. hexactis, all species of Leptasterias found in the north west Pacific Ocean. The authorities were Bush (1918), Fisher (1930), Chia (1966), Kwast (1990) and Stickle (1992). More recent morphological and behavioural studies have resulted, according to the World Register of Marine Species (WoRMS) in the retention of a single species, L. hexactis, with the other two being considered synonyms. [1] [2] WoRMS now recognizes three subspecies, L. hexactis hexactis (Stimpson, 1862) L. hexactis occidentalis Djakonov, 1938 and L. hexactis vancouveri (Perrier, 1875). [1]
Leptasterias hexactis is a rather squat starfish growing to a diameter of about 5 centimetres (2.0 in) with 6 short, broad arms. These are about as long as the disc is wide. The colour of the aboral (upper) surface varies, usually being a plain or mottled dark grey, brown or olive green colour or occasionally brick red. It is densely clad with short, mushroom-shaped spines, interspersed among which are pedicellariae (small, two-jawed pincers). The central row of spines on each arm is distinctive. The oral (under) surface is a pale colour with parallel rows of tube feet with suckers extending along the arms. [3] [4]
In California Leptasterias hexactis might be confused with Leptasterias pusilla but that species is smaller, is usually a pale grey-brown or reddish colour and has elongated, thinner arms and sharp spines. [3]
Leptasterias hexactis occurs in the intertidal zone of the north east Pacific Ocean with a range extending from the San Juan Islands in Washington to the Channel Islands of California. It favours exposed locations battered by surf and may be found at low tide under boulders and hiding among seaweed on the lower shore. Its tube feet are very adhesive and it clings securely to rocks. [4]
Leptasterias hexactis is a carnivore and is able to attack and capture surprisingly large prey items with high nutritional content. The diet includes sea cucumbers, snails, limpets, mussels, chitons and barnacles as well as carrion. Over much of its range it competes with the larger Pisaster ochraceus (ochre starfish) for food. [4]
Leptasterias hexactis is dioecious with individuals being either male or female. In Puget Sound, reproduction takes place between November and April. The eggs have yolks and between 50 and 1500 are laid, depending on the size of the female. They are fertilized by sperm that has been discharged into the water column by males. The female then holds the eggs with her tube feet in a mass near her mouth, arching her body up as she broods them. [4] She is unable to eat at this time and clings to the rock as best she can with the remaining tube feet though it may be only the tips of the arms that are available to hold her in place. While the eggs are being brooded, she tends them and keeps them clean. They are lecithotrophic and consume the yolks of their eggs as they develop. After about 40 days the eggs begin to hatch into juveniles, miniature starfish with truncated limbs. These continued to be brooded by the mother for a few weeks before setting off independently on their own. [5] If breeding has taken place in an aquarium, they can be seen crawling over the glass, and sometimes floating on the surface of the water as neuston. They will become mature in about 2 years. [4]
An echinoderm is any member of the phylum Echinodermata. The adults are recognisable by their radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Adult echinoderms 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 grouping of deuterostomes, after the chordates. Echinoderms are the largest entirely marine 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.
Mediaster aequalis is a species of sea star in the family Goniasteridae. It is native to the west coast of North America, ranging from Alaska to California. It is found in various habitats including beaches during very low tides, and at depths down to about 500 m (1,600 ft). Also known as the vermilion sea star, it is the type species of the genus Mediaster and was first described in 1857 by the American zoologist William Stimpson.
The Asteriidae are a diverse family of Asteroidea in the order Forcipulatida. It is one of three families in the order Forcipulatida.
The common starfish, common sea star or sugar starfish is the most common and familiar starfish in the north-east Atlantic. Belonging to the family Asteriidae, it has five arms and usually grows to between 10–30 cm across, although larger specimens are known. The common starfish is usually orange or brownish in color, and sometimes violet; specimens found in deeper waters are pale. The common starfish is found on rocky and gravelly substrates where it feeds on mollusks and other benthic invertebrates.
Leptasterias is a genus of starfish in the family Asteriidae. Members of this genus are characterised by having six arms although five-armed specimens sometimes occur. L. muelleri is the type species. The taxonomy of the genus is confusing and Leptasterias hexactis seems to be a species complex. Some species brood their eggs.
Solaster dawsoni, the morning sun star, is a species of starfish in the family Solasteridae. It is found on either side of the northern Pacific Ocean. It has two subspecies:
The purple sunstar, northern sunstar, or smooth sun star, Solaster endeca, is a species of starfish in the family Solasteridae.
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.
Anasterias rupicola is a species of starfish in the family Asteriidae. It is found in shallow waters in the Southern Ocean and sub-Antarctic Indian Ocean.
Leptasterias tenera is a species of starfish in the family Asteriidae. It is found on the eastern coast of North America.
Asterina gibbosa, commonly known as the starlet cushion star, is a species of starfish in the family Asterinidae. It is native to the northeastern Atlantic Ocean and the Mediterranean Sea.
Marthasterias is a genus of starfish in the family Asteriidae. It is monotypic and the only species in the genus is Marthasterias glacialis, commonly known as the spiny starfish. It is native to the eastern Atlantic Ocean.
Leptasterias muelleri, the northern starfish, is a species of starfish in the family Asteriidae. It is found in the Arctic Ocean and the northern Atlantic Ocean. It is a predator and scavenger and is unusual among starfish in that it broods its young.
Astrostole scabra, commonly called the seven-armed starfish, is a sea star in the family Asteriidae, native to New Zealand, eastern Australia and southern Australia. A frequent inhabitant of the intertidal zone also seen attached to wharf piles, it is among the larger sea-stars found in New Zealand. Adults often prey on mussels, forcing the shells open by applying pressure for long periods with the tube feet.
Epiactis lisbethae, commonly known as Lisbeth's brooding anemone, is a species of sea anemone in the family Actiniidae. It is similar in appearance to the common brooding anemone, and like it is native to shallow waters on the western coast of North America.
Epiactis fernaldi, commonly known as the Fernald brooding anemone, is a species of sea anemone in the family Actiniidae. It is native to shallow waters around the San Juan Islands off the western coast of North America.
Eupentacta quinquesemita is a species of sea cucumber, a marine invertebrate with an elongated body, a leathery skin and tentacles surrounding the mouth. It is commonly known as the stiff-footed sea cucumber or white sea cucumber, and occurs on rocky coasts in the northeastern Pacific Ocean.
Goniocidaris umbraculum is a species of cidaroid sea urchin that inhabits the continental shelf off the southern coasts of New Zealand. It is plentiful on a seabed composed of seashell and bryozoan rubble at a depth of 95 m (310 ft) off Otago.
Asterina pancerii, commonly known as the seagrass asterina, is a species of starfish in the family Asterinidae. It is native to shallow parts of the Mediterranean Sea where it is usually found in seagrass meadows.