An echinoderm is any member of the phylum Echinodermata of marine animals. The adults are recognizable by their radial symmetry, and include starfish, 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 7000 living species, making it the second-largest grouping of deuterostomes, after the chordates. Echinoderms are the largest phylum that has no freshwater or terrestrial members.
Sea urchins are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres. Their hard shells (tests) are round and spiny, usually from 3 to 10 cm across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, triggerfish, and humans.
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 occur on the seabed in all the world's oceans, from the tropics to frigid polar waters. They are found from the intertidal zone down to abyssal depths, 6,000 m (20,000 ft) below the surface.
Sea cucumbers are echinoderms from the class Holothuroidea. They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothurian species worldwide is about 1,717 with the greatest number being in the Asia Pacific region. Many of these are gathered for human consumption and some species are cultivated in aquaculture systems. The harvested product is variously referred to as trepang, namako, bêche-de-mer or balate. Sea cucumbers serve a useful role in the marine ecosystem as they help recycle nutrients, breaking down detritus and other organic matter after which bacteria can continue the degradation process.
Fish anatomy is the study of the form or morphology of fish. It can be contrasted with fish physiology, which is the study of how the component parts of fish function together in the living fish. In practice, fish anatomy and fish physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the latter dealing with how those components function together in living fish.
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.
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. From New Latin ophiurus, from Ancient Greek ὄφις + οὐρά.
Balanoglossus is an ocean-dwelling(only Marine water dwelling, not fresh water dwelling) acorn worm (Enteropneusta) genus of great zoological interest because, being a Hemichordate, it is an "evolutionary link" between invertebrates and vertebrates. Balanoglossus is a deuterostome, and resembles the Ascidians or sea squirts, in that it possesses branchial openings, or "gill slits". It has notochord in the upper part of the body and has no nerve chord. It does have a stomochord, however, which is gut chord within the collar. Their heads may be as small as per 2.5 mm (1/10 in) or as large as 5 mm (1/5 in).
The Phrynophiurida are an order of brittle stars containing the basket stars.
Ophiocanops fugiens is a living species in the brittle star family Ophiocanopidae. Though once considered to be the only one living species in this brittle star family, recent research has brought to light three specimens of Ophiocanops that differ substantially from O. fugiens. It has been regarded as the most primitive brittle star, close to Paleozoic forms, though other authors have disagreed with the view. Classification of O. fugiens is highly argued. Ophiocanops is usually placed in the order Oegophiurida or regarded as a genus incertae sedis or even given its own subclass Oegophiuridea. Some recent data suggest its relationship to the extant family Ophiomyxidae.
Radiodonta is an order of stem-group arthropods that was successful worldwide during the Cambrian period. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anomalocaridids, although the latter originally refer to the family Anomalocarididae, which previously included all species of this order but is now restricted to only a few species. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and used for a variety of functions. Radiodonts included the earliest large predators known, but they also included sediment sifters and filter feeders. Some of the most famous species of radiodonts are the Cambrian taxa Anomalocaris canadensis, Hurdia victoria, Peytoia nathorsti, and Amplectobelua symbrachiata, the Ordovician Aegirocassis benmoulai and the Devonian Schinderhannes bartelsi.
Insect morphology is the study and description of the physical form of insects. The terminology used to describe insects is similar to that used for other arthropods due to their shared evolutionary history. Three physical features separate insects from other arthropods: they have a body divided into three regions, have three pairs of legs, and mouthparts located outside of the head capsule. It is this position of the mouthparts which divides them from their closest relatives, the non-insect hexapods, which includes Protura, Diplura, and Collembola.
Vancleavea is a genus of extinct, armoured, non-archosaurian archosauriforms from the Late Triassic of western North America. The type and only known species is V. campi, named by Robert Long & Phillip A Murry in 1995. At that time, the genus was only known from fragmentary bones including osteoderms and vertebrae. However, since then many more fossils have been found, including a pair of nearly complete skeletons discovered in 2002. These finds have shown that members of the genus were bizarre semiaquatic reptiles. Vancleavea individuals had short snouts with large, fang-like teeth, and long bodies with small limbs. They were completely covered with bony plates known as osteoderms, which came in several different varieties distributed around the body. Phylogenetic analyses by professional paleontologists have shown that Vancleavea was an archosauriform, part of the lineage of reptiles that would lead to archosaurs such as dinosaurs and crocodilians. Vancleavea lacks certain traits which are present in most other archosauriforms, most notably the antorbital, mandibular and supratemporal fenestrae, which are weight-saving holes in the skulls of other taxa. However, other features clearly support its archosauriform identity, including a lack of intercentra, the presence of osteoderms, an ossified laterosphenoid, and several adaptations of the femur and ankle bones. In 2016, a new genus of archosauriform, Litorosuchus, was described. This genus resembled both Vancleavea and more typical archosauriforms in different respects, allowing Litorosuchus to act as a transitional fossil linking Vancleavea to less aberrant archosauriforms.
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.
Xyloplax medusiformis is a sea daisy, a member of an unusual group of marine taxa belonging to the phylum Echinodermata. It is found at bathyal depths in waters around New Zealand. It was first described in 1986 by Baker, Rowe and Clark and is the type taxon of the genus Xyloplax. Its generic name derives from the Greek "xylo" meaning wood and its specific name was chosen because its morphology superficially resembles that of a cnidarian medusa.
Ossicles are small calcareous elements embedded in the dermis of the body wall of echinoderms. They form part of the endoskeleton and provide rigidity and protection. They are found in different forms and arrangements in sea urchins, starfish, brittle stars, sea cucumbers, and crinoids. The ossicles and spines are the only parts of the animal likely to be fossilized after an echinoderm dies.
Microbrachius is an extinct genus of tiny, advanced antiarch placoderms closely related to the bothriolepids. Complete articulated specimens show that the armored section of the body had an average length of 2-4 cm. Species of Microbrachius are characterized by having large heads with short thoracic armor. Specimens of Microbrachius have been found in Scotland, Belarus, Estonia, and China. Specimens range in age from the Lower Devonian Late Emsian Stage to the Middle Devonian Upper Givetian Stage.
Nundasuchus is an extinct genus of crurotarsan, possibly a suchian archosaur related to Paracrocodylomorpha. Remains of this genus are known from the Middle Triassic Manda beds of southwestern Tanzania. It contains a single species, Nundasuchus songeaensis, known from a single partially complete skeleton, including vertebrae, limb elements, osteoderms, and skull fragments.
Asterolepis is an extinct genus of antiarch placoderms from the Devonian of North and South America and Europe. They were heavily armored flat-headed benthic detritivores with distinctive jointed limb-like pectoral fins and hollow spine. The armor plate gives the Asterolepis a box-like shape. Its pectoral fins are also armored but the caudal and dorsal fin are not. The first fossils were named by M. Eichwald in 1840 after noticing star-like markings on the fossils.
Astrobrachion adhaerens is a basket star in the Euryalidae family. Along with A. constrictum, it is one of only two species in the genus Astrobrachion. Both species live in association with soft corals in moderately deep water. It is endemic to the west, north and east coasts of Australia, the Kermadec Islands and Lord Howe Island.
