Cumacea is an order of small marine crustaceans of the superorder Peracarida called hooded shrimp or comma shrimp. Their unique appearance and uniform body plan makes them easy to distinguish from other crustaceans, they live in soft-bottoms such as mud and sand in the marine environment. There are more than 1,500 of species of cumaceans formally described; the species diversity of Cumacea increases with depth. Cumaceans have a enlarged cephalothorax with a carapace, a slim abdomen, a forked tail; the length of most species varies from 1 to 10 millimetres. The carapace of a typical cumacean is composed of several fused dorsal head parts and the first three somites of the thorax; this carapace encloses the appendages that serve for feeding. In most species, there are two eyes at the front side of the head shield merged into a single dorsal eye lobe; the five posterior somites of the thorax form the pereon. The pleon consists of six cylindrical somites; the first antenna has two flagella, the outer flagellum being longer than the inner one.
The second antenna is reduced in females, consists of numerous segments in males. Cumaceans have six pairs of mouthparts: one pair of mandibles, one pair of maxillules, one pair of maxillae and three pairs of maxillipeds. Cumaceans are marine crustaceans. However, some species can survive in water like brackish water. In the Caspian Sea they reach some rivers that flow into it. A few species live in the intertidal zone. Most species live only one year or less, reproduce twice in their lifetime. Deep-sea species have a slower metabolism and live much longer. Cumaceans feed on microorganisms and organic material from the sediment. Species that live in the mud filter their food, while species that live in sand browse individual grains of sand. In the genus Campylaspis and a few related genera, the mandibles are transformed into piercing organs, which can be used for predation on foraminiferans and small crustaceans. Many shallow-water species show a diurnal cycle, with males emerging from the sediment at night and swarming to the surface.
Like Amphipoda, cumaceans are an important food source for many fishes. Therefore, they are an important part of the marine food chain, they can be found on all continents. Cumaceans are a clear example of sexual dimorphism: males and females differ in their appearance. Both sexes have different ornaments on their carapace. Other differences are the length of the second antenna, the existence of pleopods in males, the development of a marsupium in females. There are more females than males, females are larger than their male counterparts. Cumaceans are epimorphic, which means that the number of body segments does not change during development; this is a form of incomplete metamorphosis. Females carry the embryos in their marsupium for some time; the larvae leave the marsupium in the manca stage, in which they are fully grown and are only missing their last pair of pereiopods. The order Cumacea has been known since 1780, when Ivan Ivanovich Lepechin described the species "Oniscus scorpioides". At the time, many scientists thought.
In 1846, they were recognised as a separate order by Henrik Nikolaj Krøyer. Twenty-five years about fifty different species had been described, there are more than 1,500 described species; the German zoologist Carl Wilhelm Erich Zimmer studied the order Cumacea intensively. The fossil record of cumaceans is sparse, but extends back into the Mississippian age. Fossil Cumaceans from the early Jurassic scarcely differ from living forms. Cumaceans belong within the class Malacostraca; the order Cumacea is subdivided into 8 families, 141 genera, 1,523 species: Bodotriidae Scott, 1901 Ceratocumatidae Calman, 1905 Diastylidae Bate, 1856 Gynodiastylidae Stebbing, 1912 Lampropidae Sars, 1878 Leuconidae Sars, 1878 Nannastacidae Bate, 1866 Pseudocumatidae Sars, 1878 One species is placed incertae sedis in the order. List of Cumacea literature Cumacea page Cumacea at Crustacea.net Cumaceans of the World Cumacea World Database
A snail is, in loose terms, a shelled gastropod. The name is most applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name snail is used for most of the members of the molluscan class Gastropoda that have a coiled shell, large enough for the animal to retract into; when the word "snail" is used in this most general sense, it includes not just land snails but numerous species of sea snails and freshwater snails. Gastropods that lack a shell, or have only an internal shell, are called slugs, land snails that have only a small shell are called semi-slugs. Snails have considerable human relevance, including as food items, as pests, as vectors of disease, their shells are used as decorative objects and are incorporated into jewelry; the snail has had some cultural significance, has been used as a metaphor. Snails that respire using a lung belong to the group Pulmonata; as traditionally defined, the Pulmonata were found to be polyphyletic in a molecular study per Jörger et al. dating from 2010.
But snails with gills form a polyphyletic group. Both snails that have lungs and snails that have gills have diversified so over geological time that a few species with gills can be found on land and numerous species with lungs can be found in freshwater. A few marine species have lungs. Snails can be found in a wide range of environments, including ditches and the abyssal depths of the sea. Although land snails may be more familiar to laymen, marine snails constitute the majority of snail species, have much greater diversity and a greater biomass. Numerous kinds of snail can be found in fresh water. Most snails have thousands of microscopic tooth-like structures located on a banded ribbon-like tongue called a radula; the radula works like a file. Many snails are herbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species are omnivores or predatory carnivores. Snails cannot absorb colored pigments when eating paper or cardboard so their feces are colored.
Several species of the genus Achatina and related genera are known as giant African land snails. The largest living species of sea snail is Syrinx aruanus; the snail Lymnaea makes decisions by using only two types of neuron: one deciding whether the snail is hungry, the other deciding whether there is food in the vicinity. The largest known land gastropod is the African giant snail Achatina achatina, the largest recorded specimen of which measured 39.3 centimetres from snout to tail when extended, with a shell length of 27.3 cm in December 1978. It weighed 900 g. Named Gee Geronimo, this snail was owned by Christopher Hudson of Hove, East Sussex, UK, was collected in Sierra Leone in June 1976. Gastropods that lack a conspicuous shell are called slugs rather than snails; some species of slug have a red shell, some have only an internal vestige that serves as a calcium repository, others have no shell at all. Other than that there is little morphological difference between slugs and snails. There are however important differences in habitats and behavior.
A shell-less animal is much more maneuverable and compressible, so quite large land slugs can take advantage of habitats or retreats with little space, retreats that would be inaccessible to a similar-sized snail. Slugs squeeze themselves into confined spaces such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground. In such retreats they are in less danger from either predators or desiccation, those are suitable places for laying their eggs. Slugs as a group are far from monophyletic; the reduction or loss of the shell has evolved many times independently within several different lineages of gastropods. The various taxa of land and sea gastropods with slug morphology occur within numerous higher taxonomic groups of shelled species. Land snails are known as an agricultural and garden pest but some species are an edible delicacy and household pets. There are a variety of snail-control measures that gardeners and farmers use in an attempt to reduce damage to valuable plants.
Traditional pesticides are still used, as are many less toxic control options such as concentrated garlic or wormwood solutions. Copper metal is a snail repellent, thus a copper band around the trunk of a tree will prevent snails from climbing up and reaching the foliage and fruit. Placing crushed egg shells on the soil around garden plants can deter snails from coming to the plants; the decollate snail will capture and eat garden snails, because of this it has sometimes been introduced as a biological pest control agent. However, this is not without problems, as the decollate snail is just as to attack and devour other gastropods that may represent a valuable part of the native fauna of the region. In French cuisine, edible snails are served for instance in Escargot à la Bourguignonne; the practice of rearing snails for food is known as heliciculture. For purposes of cultivation, the snails are kept in a
Eutrophication, or hypertrophication, is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of plants and algae. This process may result in oxygen depletion of the water body. One example is an "algal bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Eutrophication is induced by the discharge of nitrate or phosphate-containing detergents, fertilizers, or sewage into an aquatic system. Eutrophication most arises from the oversupply of nutrients, most as nitrogen or phosphorus, which leads to overgrowth of plants and algae in aquatic ecosystems. After such organisms die, bacterial degradation of their biomass results in oxygen consumption, thereby creating the state of hypoxia. According to Ullmann's Encyclopedia, "the primary limiting factor for eutrophication is phosphate." The availability of phosphorus promotes excessive plant growth and decay, favouring simple algae and plankton over other more complicated plants, causes a severe reduction in water quality.
Phosphorus is a necessary nutrient for plants to live, is the limiting factor for plant growth in many freshwater ecosystems. Phosphate adheres to soil, so it is transported by erosion. Once translocated to lakes, the extraction of phosphate into water is slow, hence the difficulty of reversing the effects of eutrophication. However, numerous literature report that nitrogen is the primary limiting nutrient for the accumulation of algal biomass; the sources of these excess phosphates are phosphates in detergent, industrial/domestic run-offs, fertilizers. With the phasing out of phosphate-containing detergents in the 1970s, industrial/domestic run-off and agriculture have emerged as the dominant contributors to eutrophication. Cultural eutrophication is the process that speeds up natural eutrophication because of human activity. Due to clearing of land and building of towns and cities, land runoff is accelerated and more nutrients such as phosphates and nitrate are supplied to lakes and rivers, to coastal estuaries and bays.
Extra nutrients are supplied by treatment plants, golf courses, farms, as well as untreated sewage in many countries. When algae die, they decompose and the nutrients contained in that organic matter are converted into inorganic form by microorganisms; this decomposition process consumes oxygen. The depleted oxygen levels in turn may lead to fish kills and a range of other effects reducing biodiversity. Nutrients may become concentrated in an anoxic zone and may only be made available again during autumn turn-over or in conditions of turbulent flow; the dead algae and the organic load carried by the water inflows in to the lake settle at its bottom and undergoes anaerobic digestion releasing greenhouse gases like methane and CO2. Some part of methane gas is consumed by the anaerobic methane oxidation bacteria which in turn works as food source to the zooplankton. In case the lake is not deficit of dissolved oxygen at all depths the aerobic methane oxidation bacteria like Methylococcus capsulatus can consume most of the methane by releasing CO2 which in turn aid the production of algae.
Thus a self-sustaining biological process can take place to generate primary food source for the phytoplankton and zooplankton depending on availability of adequate dissolved oxygen in the water bodies which are subjected to higher organic pollution loads. Adequate dissolved oxygen in water bodies is crucial for fisheries production and elimination of green house gas emissions. Enhanced growth of aquatic vegetation or phytoplankton and algal blooms disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen needed for fish and shellfish to survive; the water becomes cloudy coloured a shade of green, brown, or red. Eutrophication decreases the value of rivers and aesthetic enjoyment. Health problems can occur. Human activities can accelerate the rate. Runoff from agriculture and development, pollution from septic systems and sewers, sewage sludge spreading, other human-related activities increase the flow of both inorganic nutrients and organic substances into ecosystems.
Elevated levels of atmospheric compounds of nitrogen can increase nitrogen availability. Phosphorus is regarded as the main culprit in cases of eutrophication in lakes subjected to "point source" pollution from sewage pipes; the concentration of algae and the trophic state of lakes correspond well to phosphorus levels in water. Studies conducted in the Experimental Lakes Area in Ontario have shown a relationship between the addition of phosphorus and the rate of eutrophication. Humankind has increased the rate of phosphorus cycling on Earth by four times due to agricultural fertilizer production and application. Between 1950 and 1995, an estimated 600,000,000 tonnes of phosphorus was applied to Earth's surface on croplands. Although eutrophication is caused by human activities, it can be a natural process in lakes. Eutrophy occurs for instance. Paleolimnologists now recognise that climate change and other external influences are critical in regulating the natural productivity of lakes; some lakes demonstrate the reverse process, becoming less nutrient rich with time.
The main difference between natural and anthropogenic eutrophication is that the natural process is slow, occurring on geological time scales. Eutrophication is a common phenomenon i
A stream is a body of water with surface water flowing within the bed and banks of a channel. The stream encompasses surface and groundwater fluxes that respond to geological, geomorphological and biotic controls. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams are called rivers. Streams are important as conduits in the water cycle, instruments in groundwater recharge, corridors for fish and wildlife migration; the biological habitat in the immediate vicinity of a stream is called a riparian zone. Given the status of the ongoing Holocene extinction, streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity; the study of streams and waterways in general is known as surface hydrology and is a core element of environmental geography. Brook A stream smaller than a creek one, fed by a spring or seep, it is small and forded. A brook is characterised by its shallowness.
Creek In North America and New Zealand, a small to medium-sized natural stream. Sometimes navigable by motor craft and may be intermittent. In parts of Maryland, New England, the UK and India, a tidal inlet in a salt marsh or mangrove swamp, or between enclosed and drained former salt marshes or swamps. In these cases, the stream is the tidal stream, the course of the seawater through the creek channel at low and high tide. River A large natural stream, which may be a waterway. Runnel the linear channel between the parallel ridges or bars on a shoreline beach or river floodplain, or between a bar and the shore. Called a swale. Tributary A contributory stream, or a stream which does not reach a static body of water such as a lake or ocean, but joins another river. Sometimes called a branch or fork. There are a number of regional names for a stream. Allt is used in Highland Scotland. Beck is used in Lincolnshire to Cumbria in areas which were once occupied by the Danes and Norwegians. Bourne or winterbourne is used in the chalk downland of southern England.
Brook. Burn is used in North East England. Gill or ghyll is seen in Surrey influenced by Old Norse; the variant "ghyll" is used in the Lake District and appears to have been an invention of William Wordsworth. Nant is used in Wales. Rivulet is a term encountered in Victorian era publications. Stream Syke is used in lowland Cumbria for a seasonal stream. Branch is used to name streams in Virginia. Creek is common throughout the United States, as well as Australia. Falls is used to name streams in Maryland, for streams/rivers which have waterfalls on them if such falls have a small vertical drop. Little Gunpowder Falls and The Jones Falls are rivers named in this manner, unique to Maryland. Kill in New York, Pennsylvania and New Jersey comes from a Dutch language word meaning "riverbed" or "water channel", can be used for the UK meaning of'creek'. Run in Ohio, Michigan, New Jersey, Virginia, or West Virginia can be the name of a stream. Run in Florida is the name given to streams coming out of small natural springs.
River is used for larger springs like the Silver Rainbow River. Stream and brook are used in Midwestern states, Mid-Atlantic states, New England. Bar A shoal that develops in a stream as sediment is deposited as the current slows or is impeded by wave action at the confluence. Bifurcation A fork into two or more streams. Channel A depression created by constant erosion. Confluence The point at which the two streams merge. If the two tributaries are of equal size, the confluence may be called a fork. Drainage basin The area of land. A large drainage basin such as the Amazon River contains many smaller drainage basins. Floodplain Lands adjacent to the stream that are subject to flooding when a stream overflows its banks. Gaging station A site along the route of a stream or river, used for reference marking or water monitoring. Headwaters The part of a stream or river proximate to its source; the word is most used in the plural where there is no single point source. Knickpoint The point on a stream's profile where a sudden change in stream gradient occurs.
Mouth The point at which the stream discharges via an estuary or delta, into a static body of water such as a lake or ocean. Pool A segment where the water is deeper and slower moving. Rapids A turbulent, fast-flowing stretch of a stream or river. Riffle A segment where the flow is shallower and more turbulent. River A large natural stream, which may be a waterway. Run A somewhat smoothly flowing segment of the stream. Source The spring, or other point of origin of a stream. Spring The point at which a stream emerges from an underground course through unconsolidated sediments or through caves. A stream can with caves, flow aboveground for part of its course, underground for part of its course. Stream bed The bottom of a stream. Stream corridor Stream, its floodplains, the transitional upland fringe Streamflow The water moving through a stream channel. Thalweg The river's longitudinal section, or the line joining the deepest point in the channel at each stage from source to mouth. Waterfall or cascade The fall of water where the stream goes over a sudden drop called a knickpoint.
The stream expends kinetic energy in "trying" to eliminate the
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 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. Like all echinoderms, sea cucumbers have an endoskeleton just below the skin, calcified structures that are reduced to isolated microscopic ossicles joined by connective tissue. In some species these can sometimes be enlarged to flattened plates. In pelagic species such as Pelagothuria natatrix, the skeleton is absent and there is no calcareous ring.
The sea cucumbers are named after their resemblance to the fruit of the cucumber plant. Most sea cucumbers, as their name suggests, have a soft and cylindrical body, more or less lengthened, rounded off and fat in the extremities, without solid appendages, their shape ranges from spherical for "sea apples" to serpent-like for Apodida or the classic sausage-shape, while others resemble caterpillars. The mouth is surrounded by tentacles. Holothurians measure between 10 and 30 centimetres long, with extremes of some millimetres for Rhabdomolgus ruber and up to more than 3 metres for Synapta maculata; the largest American species, Holothuria floridana, which abounds just below low-water mark on the Florida reefs, has a volume of well over 500 cubic centimeters, 25–30 cm long. Most possess five rows of tube feet; the podia on the dorsal surface have no locomotive role, are transformed into papillae. At one of the extremities opens a rounded mouth surrounded with a crown of tentacles which can be complex in some species.
Holothurians do not look like other echinoderms at first glance, because of their tubular body, without visible skeleton nor hard appendixes. Furthermore, the fivefold symmetry, classical for echinoderms, although preserved structurally, is doubled here by a bilateral symmetry which makes them look like chordates. However, a central symmetry is still visible in some species through five'radii', which extend from the mouth to the anus, on which the tube feet are attached. There is thus no "oral" or "aboral" face as for sea stars and other echinoderms, but the animal stands on one of its sides, this face is called trivium, while the dorsal face is named bivium. A remarkable feature of these animals is the "catch" collagen; this can be loosened and tightened at will, if the animal wants to squeeze through a small gap, it can liquefy its body and pour into the space. To keep itself safe in these crevices and cracks, the sea cucumber will hook up all its collagen fibers to make its body firm again.
The most common way to separate the subclasses is by looking at their oral tentacles. Order Apodida have a slender and elongate body lacking tube feet, with up to 25 simple or pinnate oral tentacles. Aspidochirotida are the most common sea cucumbers encountered, with a strong body and 10–30 leaf like or shield like oral tentacles. Dendrochirotida are filter-feeders, with 8 -- 30 branched oral tentacles. Sea cucumbers are 10 to 30 cm in length, although the smallest known species are just 3 mm long, the largest can reach 3 meters; the body ranges from spherical to worm-like, lacks the arms found in many other echinoderms, such as starfish. The anterior end of the animal, containing the mouth, corresponds to the oral pole of other echinoderms, while the posterior end, containing the anus, corresponds to the aboral pole. Thus, compared with other echinoderms, sea cucumbers can be said to be lying on their side; the body of a holothurian is cylindrical. It is radially symmetrical along its longitudinal axis, has weak bilateral symmetry transversely with a dorsal and a ventral surface.
As in other Echinozoans, there are five ambulacra separated by five ambulacral grooves, the interambulacra. The ambulacral grooves bear four rows of tube feet but these are diminished in size or absent in some holothurians on the dorsal surface; the two dorsal ambulacra make up the bivium. At the anterior end, the mouth is surrounded by a ring of tentacles which are retractable into the mouth; these may be simple, branched or arborescent. They are known as the introvert and posterior to them there is an internal ring of large calcareous ossicles. Attached to this are five bands of muscle running internally longitudinally along the ambulacra. There are circular muscles, contraction of which cause the animal to elongate and the introvert to extend. Anterior to the ossicles lie further muscles; the body wall consists of an epidermis and a dermis and contains smaller c
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage finds these names being applied to ophiuroids, which are referred to as brittle stars or basket stars. About 1,500 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 6,000 m below the surface. Starfish are marine invertebrates, they have a central disc and five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny, is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface, they are opportunistic feeders and are predators on benthic invertebrates. Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding.
They can reproduce both sexually and asexually. Most can regenerate damaged parts or lost arms and they can shed arms as a means of defence; the Asteroidea occupy several significant ecological roles. Starfish, such as the ochre sea star and the reef sea star, have become known as examples of the keystone species concept in ecology; the tropical crown-of-thorns starfish is a voracious predator of coral throughout the Indo-Pacific region, the northern Pacific sea star is considered to be one of the world's 100 worst invasive species. The fossil record for starfish is ancient, dating back to the Ordovician around 450 million years ago, but it is rather sparse, as starfish tend to disintegrate after death. Only the ossicles and spines of the animal are to be preserved, making remains hard to locate. With their appealing symmetrical shape, starfish have played a part in literature, legend and popular culture, they are sometimes collected as curios, used in design or as logos, in some cultures, despite possible toxicity, they are eaten.
Most starfish have five arms that radiate from a central disc. Some species have six or seven arms and others have 10–15 arms; the Antarctic Labidiaster annulatus can have over fifty. Having descended from bilateral organisms, starfish move in a bilateral fashion, with certain arms acting like the front of the animal; the body wall consists of a thin cuticle, an epidermis consisting of a single layer of cells, a thick dermis formed of connective tissue and a thin coelomic myoepithelial layer, which provides the longitudinal and circular musculature. The dermis contains an endoskeleton of calcium carbonate components known as ossicles; these are honeycombed structures composed of calcite microcrystals arranged in a lattice. They vary in form, with some bearing external granules and spines, but most are tabular plates that fit neatly together in a tessellated manner and form the main covering of the aboral surface; some are specialised structures such as the madreporite and paxillae. Pedicellariae are compound ossicles with forceps-like jaws.
They remove debris from the body surface and wave around on flexible stalks in response to physical or chemical stimuli while continually making biting movements. They form clusters surrounding spines. Paxillae are umbrella-like structures found on starfish; the edges of adjacent paxillae meet to form a false cuticle with a water cavity beneath in which the madreporite and delicate gill structures are protected. All the ossicles, including those projecting externally, are covered by the epidermal layer. Several groups of starfish, including Valvatida and Forcipulatida, possess pedicellariae. In Forcipulatida, such as Asterias and Pisaster, they occur in pompom-like tufts at the base of each spine, whereas in the Goniasteridae, such as Hippasteria phrygiana, the pedicellariae are scattered over the body surface; some are thought to assist in defence, while others aid in feeding or in the removal of organisms attempting to settle on the starfish's surface. Some species like Labidiaster annulatus, Rathbunaster californicus and Novodinia antillensis use their large pedicellariae to capture small fish and crustaceans.
There may be papulae, thin-walled protrusions of the body cavity that reach through the body wall and extend into the surrounding water. These serve a respiratory function; the structures are supported by collagen fibres set at right angles to each other and arranged in a three-dimensional web with the ossicles and papulae in the interstices. This arrangement enables both easy flexion of the arms by the starfish and the rapid onset of stiffness and rigidity required for actions performed under stress; the water vascular system of the starfish is a hydraulic system made up of a network of fluid-filled canals and is concerned with locomotion, food manipulation and gas exchange. Water enters the system through the madreporite, a porous conspicuous, sieve-like ossicle on the aboral surface, it is linked through a stone canal lined with calcareous material, to a ring canal around the mouth opening. A set of radial canals leads off this. There are short lateral canals branching off alternately to either side of the radial canal, each ending in an ampulla.
These bulb-shaped organs are joined to tube feet on the exterior of the animal by short linking canals that pass through ossicles in the ambulacral groove. There are two rows of tube feet but in some species, the lateral c