Full Answer
Is Asteroidea and Ophiuroidea sister taxa?
Asteroidea and Ophiuroidea (brittle stars) are sister taxa and together comprise the Asterozoa clade. Simplified overview of echinoderm phylogeny based in part on the hypothesis of relationships presented by Reich et al. (2015).
What is the difference between asteroids and ophiuroids?
The main difference between asteroids and ophiuroids is the way that the rays, or arms, attach to the body. In ophiuroids, the arms are not joined to each other and the body and arms are clearly separated, but in the asteroids the arms are joined to each other and the boundary between arms and the central disc is blurred.
What are the characteristics of ophiuroid stars?
Arms: The arms of ophiuroids are long. They are sharply started from the central disk. It gives the central disk a pentagonal shape. Brittle stars have unbranched arms. It has a central disk that ranges in size from I to 3 cm. The arms of the basket stars are branched repeatedly.
What are Ophiuroidea?
Ophiuroidea are the most speciose living echinoderm class, inhabiting all regions of the world’s oceans, and are often found in dense aggregations at great depths (>5,000m). Sometimes there are so many that they look like a carpet or meadow covering the entire ocean bottom.
What's the difference between Asteroidea and Ophiuroidea?
But within the phylum, sea stars and brittle stars are in different classes. Sea stars are in the class Asteroidea, where brittle stars are in Ophiuroidea, which also includes basket stars.
What does a Ophiuroidea do?
ophis = serpent) -- an ophiuroid locomotes by using two rays to produce a rowing motion. The rays of basket stars branch. Ophiuroids possess considerable powers of regeneration: an arm can be regenerated at any point, but if the disc is totally separated from all arms, the animal will die.
What is Asteroidea in biology?
a class of star-shaped ECHINODERMS which have a basic pentaradiate shape (a five-sided RADIAL SYMMETRY), e.g. starfish.
What are 3 differences between starfish and a brittle star?
The key difference between starfish and brittle star is the manner in which they move. Starfish uses tube feet to move whereas brittle star uses its long arms to move. Moreover, starfish have special features such as the presence of ampullae and parapodia whereas brittle star lacks those.
What is an example of Ophiuroidea?
Basket starsOphiuridaOphiothrix fragilisOphiacant...OphiopholisOphiocano... fugiensBrittle stars/Lower classificationsOphiuroids are a large group (over 1600 species) of echinoderms that includes the brittle stars (Ophiurida) and basket stars (Euryalida). The more familiar Ophiurida, or brittle stars, usually have five arms and superficially resemble true starfish (Asteroidea).
What are the characteristics of Asteroidea?
Major Attributes:Generally a flattened body shape.Adult is radially symetrical while the young is bilateral.Usually 5 ( up to 40 ) arms.Freely mobile.Tube feet for locomotion.Regenerative abilities.
Which is an example of an Asteroidea member?
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (/ˌæstəˈrɔɪdiə/).
Who are Asteroidea and how many species are there?
The Asteroidea (also known as sea stars or starfish) are among the most diverse and familiar of the living Echinodermata, including over 1800 species from every ocean basin in the world, including the Atlantic, Indian, and Pacific as well as the Arctic and the Southern Ocean, inhabiting intertidal to 6000 m abyssal ...
What is the Asteroidea habitat?
Habitat and Distribution Asteroidea can be found in oceans around the world, inhabiting a wide range of water depths, from the intertidal zone to the deep sea.
Why are brittle stars called brittle?
Brittle stars are named for the ease with which their arms break off when touched; these animals, known collectively as ophioroids, are also called serpent stars (ophis means snake in Greek) because their long arms resemble serpents.
What is another name for the brittle star?
brittle star, also called serpent star, any of the 2,100 living species of marine invertebrates constituting the subclass Ophiuroidea (phylum Echinodermata). Their long, thin arms—usually five and often forked and spiny—are distinctly set off from the small disk-shaped body.
Can you eat brittle star?
Brittle stars are not used as food, though they are not toxic, because of their strong skeleton. Even if some species have blunt spines, no brittlestar is known to be dangerous, nor venomous.
Why are asteroids called neoasteroidea?
Living asteroids have been lumped together and called Neoasteroidea because of their differences from Paleozoic forms. The body of a sea star is made of a central disk with arms radiating outwards, each referred to as a ray. Sea stars commonly have five rays, but some species have far more and these are often in multiples of five, ...
When did asteroid groups start?
Starting in the Triassic, and increasingly so during the Jurassic, modern asteroid groups (e.g., Neoasteroidea) became prevalent. Photograph of a fossil Pliocene sea star ( Heliaster microbrachius) from the Florida Museum of Natural History (FMNH).
What is the name of the class of sea stars?
Members of class Asteroidea are commonly known as sea stars or starfish (though they certainly aren't fish). In Greek, Asteroidea means "star-like" and, as the name suggests, this class has a pentaradial body plan and is composed largely of mobile species. Asteroidea and Ophiuroidea (brittle stars) are sister taxa and together comprise the Asterozoa clade.
What was the impact of the end-Permian extinction on the asteroid fauna?
As with other groups of echinoderms (e.g., crinoids, echinoids), the end-Permian extinction led to a dramatic change in the asteroid fauna. Paleozoic taxa only rarely survived the event and the modern asteroid fauna largely evolved from those few taxa, creating distinct Paleozoic and post-Paleozoic faunas.
What is the disease that causes sea stars to fall apart?
Unfortunately, several sea star populations, including those that are keystone species, are suffering from a sickness called "sea star wasting disease.". Sea stars with this disease disintegrate and fall apart without being able to regenerate limbs like a normal sea star would.
What is the predatory system of sea stars?
Sea stars as predators. Sea stars are opportunistic omnivores and terrifying predators, crawling along the ocean bottom with a downward-facing mouth. Most have a one-way digestive system, meaning that food enters and waste exits from the same opening.
What are the most sensitive parts of a sea star's body?
A sea star’s tube feet can also sense or 'taste' chemicals (chemoreception), water currents, and feel objects around them (mechanoreception). Their tube feet are the most sensitive parts of their bodies.
What is the mouth of a sea star?
The mouth is on the bottom (ventral, oral surface) surface of the animal, the anal and five (pentaradial) gonadal openings on the top (dor sal, aboral surface). Many sea stars (e.g. Asterias) are highly predatory and consume large numbers of animals even slower than they are e.g. molluscs.
What phylum are echinoderms in?
Echinoderms belong to the phylum Echinodermata having 5 classes namely Crinoidea (Sea lilies and Feather stars), Ophiuroidea (Brittle stars and basket stars), Asteroidea (Sea stars), Echinoidea (Sea urchins) and Holothuoidea (Sea cucumbers) (Fig. 8.11 ). They are benthic and found in all depth of the oceans around the world.
What are the five clades of echinodermata?
Echinodermata has five well-defined clades, Crinoidea (sea lilies and feather stars), Op hiuroidea (basket stars and brittle stars), Asteroidea (starfishes), Echinoidea (sea urchins, sand dollars, and sea biscuits), and Holothuroidea (sea cucumbers). Sea urchins appear to be the only clade in this phylum that uses acquired germ line determination mechanisms. All other echinoderms appear instead to specify their germ line late in development, likely necessitating inductive mechanisms. Sea stars have been the most intensively studied clade outside of echinoids, and the site of germ line formation appears to be within the posterior enterocoele. This structure buds off the endoderm following gastrulation and becomes progressively well defined by mRNAs of germ line factors (e.g., Vasa, Nanos, Piwi) and the absence of somatic markers (e.g., Blimp). Thus, although less is known about this group of animals in general than in the sea urchin, this phylum lends itself well to understanding both the acquired mechanism as seen in flies, roundworms, and fish, as well as the inductive mechanism seen in, for example, mammals. With the many manipulations feasible in sea stars, one may be able to more readily dissect inductive mechanisms for germ line determination and contribute to those studies which instead rely largely on genetic manipulations.
What are the different types of echinoderms?
Echinoderms, which are exclusively marine animals, are divided into five classes, the Asteroidea (starfishes), Ophiuroidea (serpent-stars), Echinoidea (sea-urchins, heart-urchins, and sand-dollars), Holothuroidea (sea-cucumbers), and Crinoidea (sea-lilies and feather-stars). The male and female gametes, fertilized eggs, and embryos of echinoids have been one of the major materials for analyses of the mechanisms of gametes and in handling them in laboratories. Especially in sea urchins, both eggs and spermatozoa are readily used in fertilization experiments and can be obtained easily by injecting isotonic potassium chloride into the body cavity or by providing brief electrical stimulation. This is because sea urchin oocytes have already accomplished meiotic maturation within the ovary during the breeding season long before spawning occurs. However, because of the completion of meiosis within the ovary, sea urchin eggs are not suitable for analytical investigations on the mechanism of oocyte maturation. In contrast, in starfish, meiosis is arrested at the prophase of the first maturation division in fully grown oocytes just before spawning, and a ripe ovary contains a large number of such oocytes of almost equal size. Furthermore, in the starfish Patiria ( Asterina) pectinifera, the time required for spawning and breakdown of germinal vesicles under the influence of some active substances is relatively short, less than 30 min, and the process can be observed using a microscope when oocytes are isolated in seawater. Thus, starfish is an suitable material for elucidating the mechanisms of oocyte maturation and spawning (ovulation). This article reviews the endocrine regulation of oocyte maturation and ovulation in starfish. Oocyte growth is also briefly described.
How many species are in the echinoderm phylum?
Echinoderms (Phylum Echinodermata) are a diverse, exclusively marine group of invertebrates that consists of over 13,000 extinct species (15 classes) and 7,000 extant described species within five classes (Asteroidea, Echinoidea, Holothuroidea, Ophiuroidea and Crinoidea). Echinoderms are ubiquitous within the marine environment, and members of the phyla can often be long-lived, a numerically dominant component of the benthic macrofauna, and a keystone species within regions they occupy. Consequently, processes that impact on the population dynamics of these organisms can, and do, influence marine communities and ecosystems. Echinoderms have a complex life cycle, alternating between the long-lived adult stage and the short-lived embryonic and larval stages. Within this general reproductive pattern is a range of life-history strategies, including brooding and vivipary. Echinoderm gametes are readily obtained and have played a pivotal role in enhancing our understanding of reproductive processes such as fertilisation and embryonic development, including a significant contribution to our understanding of the effects of UVR on reproduction.
How do echinoderms develop?
Asteroid echinoderms typically develop via either feeding or non-feeding planktonic stages, or in benthic broods protected by a parent. All species with feeding (planktotrophic) larvae develop through a bipinnaria stage; most also have a subsequent brachiolaria stage ( McEdward & Miner, 2001; Fig. 5 ).
Which echinoderms are the most distant from each other?
Well-preserved echinoderm fossils suggest that crinoids diverged first from a common ancestor, and that they are the most distant from the four other echinoderm classes, in which asteroids, ophiuroids, echinoids, and holothuroids emerged in this order ( Fig. 3.5 ).
What is the name of the group of echinoderms that are starfish?
Introduction to the Asteroidea. True starfish are classified in the Asteroidea, a group of echinoderms. Unlike the superficially similar brittle stars (Ophiuroidea), true starfish have no sharp demarcation between arms and central body, and they move using tube feet rather than wriggling movements of the whole arms.
Where did the starfish come from?
True starfish and ophiuroids shared a common ancestor in the Ordovician; the fossil starfish pictured above is much more recent, coming from the Eocene of California. Most starfish are predators, feeding on sessile or slow-moving prey such as mollusks and barnacles.
What are ophiuroids?
Ophiuroids are a large group (over 1600 species) of echinoderms that includes the brittle stars (Ophiurida) and basket stars (Euryalida). The more familiar Ophiurida, or brittle stars, usually have five arms and superficially resemble true starfish (Asteroidea).
When did ophiuroids appear?
Ophiuroids and asteroids probably shared a common ancestor. Early members of both appear in the early Ordovician , roughly 500 million years ago. Ophiuroids are not common fossils; as you might expect from the name "brittle star", ophiuroids rapidly fall to pieces after death, and are rarely preserved whole.
Where do ophiuroids live?
Ophiuroids are common in many shallow-water marine habitats , and include a few species which can adapt to brackish water, which is quite unusual for echinoderms. Ophiuroids are dominant in many parts of the deep sea, where in certain regions the bottom may swarm with brittle starts. Basket stars also tend to live in deeper water.
What is the name of the extinct group of brittle stars?
Furcaster belongs to an extinct group of brittle stars, the Oegophuroidea. Instead of a single chain of "vertebrae" supporting the arms, oegophiuroids had two rows of supports alternating down each arm. This gave the arms a "zippered" appearance.
What is an ophiuroid?
Ophiuroids are opportunistic eaters with a one-way digestive system. Many, like the basket stars (another kind of ophiuroid; see more about this group below), take advantage of floating particles and plankton, which they capture with their large branched arms. Others sense out decaying organisms. However, with a mouth that contains five jaw-like plates, they can be efficient predators of crustaceans and other small invertebrates. Watch the videos below!
What order of ophiuroids are there?
As discussed by Chen and McNamara (2006), four orders of ophiuroids have been identified from the Paleozoic, including Stenurida, O egophiurida, Phrynophiurida, and Ophiurida. The Stenurida are known exclusively from the Ordovician to Devonian, but each of the other orders is represented in the Cenozoic.
What is the name of the brittle star?
Ophiuroidea are commonly known as brittle stars based on the fragile nature of their snake-like arms. These serpentine arms in turn give them their scientific name: in Greek, "ophis" means snake and "oura" means tail. The morphology of this class follows the radial, mobile form of Deline et al. (2020).
What is the fossil record of an ophiuroid?
The ophiuroid fossil record, like that of the asteroids, is characterized by its incompleteness, particularly during the Paleozoic. This incompleteness is driven largely by the fragile nature of these “brittle stars” and by their occurrence in hard-substrate environments with poor preservational potential. Nonetheless, ophiuroids first appear in the fossil record during the Ordovician, much like the other four living classes of echinoderms. As discussed on the Asteroidea page, it has been hypothesized that ophiuroids and asteroids evolved from the Somasteroidea, an extinct asterozoan. Confirmation of this hypothesis is, however, hindered by the incompleteness of the echinoderm fossil record from the Ordovician and Cambrian.
What is the most speciose living echinoderm class?
Ophiuroidea are the most speciose living echinoderm class, inhabiting all regions of the world’s oceans, and are often found in dense aggregations at great depths (>5,000m). Sometimes there are so many that they look like a carpet or meadow covering the entire ocean bottom.
What is bioluminescence in ophiuroids?
Bioluminescence is a common characteristic of ophiuroids. Research has shown this to be useful in anti-predatory tactics. Specialized cells called photocytes help emit these bioluminescent displays. Other echinoderm classes, including Holothuroidea, Crinoidea, and Asteroidea, also have bioluminescent species.
Where is the fossil of the brittle star?
Large accumulation of the fossilized legs of the brittle star (ophiuroid) Amphiura sanctaecrucis from the Miocene Santa Margarita Formation of San Luis Obispo County, California (PRI 81281). Specimen is from the research collections of the Paleontological Research Institution, Ithaca, New York (PRI 81281).
Abstract
Reparative regeneration is defined as the replacement of lost adult body parts and is a phenomenon widespread yet highly variable among animals. This raises the question of which key cellular and molecular mechanisms have to be implemented in order to efficiently and correctly replace entire body parts in any animal.
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About this chapter
Ben Khadra Y. et al. (2018) Regeneration in Stellate Echinoderms: Crinoidea, Asteroidea and Ophiuroidea. In: Kloc M., Kubiak J. (eds) Marine Organisms as Model Systems in Biology and Medicine. Results and Problems in Cell Differentiation, vol 65. Springer, Cham. https://doi.org/10.1007/978-3-319-92486-1_14
What is the name of the star that is grasped by an arm?
Regeneration and Asexual reproduction. Ophiuroids can regenerate lost arms. If a brittle star is grasped by an arm, the contraction of certain muscles separate the arm form the body. Hence they are named as brittle star.
What is the most diverse group of echinoderms?
The class Ophiuroidea includes the basket stars and the brittle stars. It has two thousand species. Thus it is the most diverse group of echinoderms. But they have small body size. They live in crevices in rocks and coral. Or they are attached to algae. That is why they are not taken as an important group. 1.
Do brittle stars have a central disk?
Brittle stars have unbranched arms. It has a central disk that ranges in size from I to 3 cm. The arms of the basket stars are branched repeatedly. 2. The dermal branchiae and pedicellariae are absent in ophiuroids. 3. Tube feet: The tube feet of ophiuroids lack suction disks and ampullae. Some muscles are associated with the base of a tube foot.
