In biology, setae are any of a number of different bristle- or hair-like structures on living organisms. Annelid setae are stiff, they help, for example, earthworms to attach to the surface and prevent backsliding during peristaltic motion. These hairs make it difficult to pull a worm straight from the ground. Setae in oligochaetes are composed of chitin, they are classified according to the limb. Crustaceans have mechano- and chemosensory setae. Setae are present on the mouthparts of crustaceans and can be found on grooming limbs. In some cases, setae are modified into scale like structures. Setae on the legs of krill and other small crustaceans help them to gather phytoplankton, it allows them to be eaten. Setae on the integument of insects are unicellular, meaning that each is formed from a single epidermal cell of a type called a trichogen meaning "bristle generator", they are at first hollow and in most forms remain hollow. They grow through and project through a secondary or accessory cell of a type called a tormogen, which generates the special flexible membrane that connects the base of the seta to the surrounding integument.
Depending on their form and function, setae may be called hairs, chaetae, or scales. The setal membrane is not cuticularized and movement is possible; some insects, such as Eriogaster lanestris larvae, use setae as a defense mechanism, as they can cause dermatitis when they come into contact with skin. The pads on a gecko's feet are small hair-like processes that play a role in the animal's ability to cling to vertical surfaces; the micrometer-scale setae branch into nanometer-scale projections called spatulae. Gekko's seta: According to Kellar Autumn, "Two front feet of a tokay gecko can withstand 20.1 N of force parallel to the surface with 227 mm2 of pad area. The foot of a tokay bears 3600 tetrads of setae per mm2, or 14,400 setae per mm2 - Consequently, a single seta should produce an average force of 6-2 pN, an average shear stress of 0-090 N mm−l. However, single setae proved both much less sticky and much more sticky than predicted by whole animal measurements, under varying experimental conditions, implying that attachment and detachment in gecko setae are mechanically controlled."
In mycology, "setae" refer to dark brown, thick-walled, thorn-like cystidia found in corticioid and poroid fungi in the family Hymenochaetaceae. Though microscopic, the setae of some species may be sufficiently prominent to be visible with a hand lens. In botany, "seta" refers to the stalk supporting the capsule of a moss or liverwort, supplying it with nutrients; the seta is part of the sporophyte and has a short foot embedded in the gametophyte on which it is parasitic. Setae are not present in all mosses, but in some species they may reach 15 to 20 centimeters in height. In the diatom family Chaetocerotaceae, "seta" refers to the hairlike outgrowths of the valve, i.e. of the face of the cells. These setae have a different structure than the valve; such setae may prevent rapid sinking and protect the cells from grazing. Synthetic setae are a class of synthetic adhesives that detach at will, sometimes called resetable adhesives, yet display substantial stickiness; the development of such synthetic materials is a matter of current research.
Chaeta Synthetic setae Van der Waals force
Algae is an informal term for a large, diverse group of photosynthetic eukaryotic organisms that are not closely related, is thus polyphyletic. Including organisms ranging from unicellular microalgae genera, such as Chlorella and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata and phloem, which are found in land plants; the largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example and the stoneworts. No definition of algae is accepted. One definition is that algae "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells". Although cyanobacteria are referred to as "blue-green algae", most authorities exclude all prokaryotes from the definition of algae.
Algae constitute a polyphyletic group since they do not include a common ancestor, although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, the roots and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy; some unicellular species of green algae, many golden algae, euglenids and other algae have become heterotrophs, sometimes parasitic, relying on external energy sources and have limited or no photosynthetic apparatus.
Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery derived from cyanobacteria that produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago. The singular alga retains that meaning in English; the etymology is obscure. Although some speculate that it is related to Latin algēre, "be cold", no reason is known to associate seaweed with temperature. A more source is alliga, "binding, entwining"; the Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it. The Latinization, fūcus, meant the cosmetic rouge; the etymology is uncertain, but a strong candidate has long been some word related to the Biblical פוך, "paint", a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean.
It could be any color: black, green, or blue. Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used; the name Fucus appears in a number of taxa. The algae contain chloroplasts. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events; the table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members; some retain plastids, but not chloroplasts. Phylogeny based on plastid not nucleocytoplasmic genealogy: Linnaeus, in Species Plantarum, the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are considered among algae.
In Systema Naturae, Linnaeus described the genera Volvox and Corallina, a species of Acetabularia, among the animals. In 1768, Samuel Gottlieb Gmelin published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the new binomial nomenclature of Linnaeus, it included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey and Lamouroux were the first to divide macroscopic algae into four divisions based on their pigmentation; this is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae, brown algae, green algae, Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers studying the Infusoria. Unlike macroalgae, which were viewed as plants, microalgae were considered animals because they are motile; the nonmotile microalgae were sometimes seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-D
Heart rate is the speed of the heartbeat measured by the number of contractions of the heart per minute. The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide, it is equal or close to the pulse measured at any peripheral point. Activities that can provoke change include physical exercise, anxiety, stress and ingestion of drugs; the American Heart Association states. Tachycardia is a fast heart rate, defined as above 100 bpm at rest. Bradycardia is a slow heart rate, defined as below 60 bpm at rest. During sleep a slow heartbeat with rates around 40 -- 50 bpm is considered normal; when the heart is not beating in a regular pattern, this is referred to as an arrhythmia. Abnormalities of heart rate sometimes indicate disease. While heart rhythm is regulated by the sinoatrial node under normal conditions, heart rate is regulated by sympathetic and parasympathetic input to the sinoatrial node; the accelerans nerve provides sympathetic input to the heart by releasing norepinephrine onto the cells of the sinoatrial node, the vagus nerve provides parasympathetic input to the heart by releasing acetylcholine onto sinoatrial node cells.
Therefore, stimulation of the accelerans nerve increases heart rate, while stimulation of the vagus nerve decreases it. Due to individuals having a constant blood volume, one of the physiological ways to deliver more oxygen to an organ is to increase heart rate to permit blood to pass by the organ more often. Normal resting heart rates range from 60-100 bpm. Bradycardia is defined as a resting heart rate below 60 bpm. However, heart rates from 50 to 60 bpm are common among healthy people and do not require special attention. Tachycardia is defined as a resting heart rate above 100 bpm, though persistent rest rates between 80–100 bpm if they are present during sleep, may be signs of hyperthyroidism or anemia. Central nervous system stimulants such as substituted amphetamines increase heart rate. Central nervous system depressants or sedatives decrease the heart rate. There are many ways in which the heart rate slows down. Most involve stimulant-like endorphins and hormones being released in the brain, many of which are those that are'forced'/'enticed' out by the ingestion and processing of drugs.
This section discusses target heart rates for healthy persons and are inappropriately high for most persons with coronary artery disease. The heart rate is rhythmically generated by the sinoatrial node, it is influenced by central factors through sympathetic and parasympathetic nerves. Nervous influence over the heartrate is centralized within the two paired cardiovascular centres of the medulla oblongata; the cardioaccelerator regions stimulate activity via sympathetic stimulation of the cardioaccelerator nerves, the cardioinhibitory centers decrease heart activity via parasympathetic stimulation as one component of the vagus nerve. During rest, both centers provide slight stimulation to the heart; this is a similar concept to tone in skeletal muscles. Vagal stimulation predominates as, left unregulated, the SA node would initiate a sinus rhythm of 100 bpm. Both sympathetic and parasympathetic stimuli flow through the paired cardiac plexus near the base of the heart; the cardioaccelerator center sends additional fibers, forming the cardiac nerves via sympathetic ganglia to both the SA and AV nodes, plus additional fibers to the atria and ventricles.
The ventricles are more richly innervated by sympathetic fibers than parasympathetic fibers. Sympathetic stimulation causes the release of the neurotransmitter norepinephrine at the neuromuscular junction of the cardiac nerves; this shortens the repolarization period, thus speeding the rate of depolarization and contraction, which results in an increased heartrate. It opens chemical or ligand-gated sodium and calcium ion channels, allowing an influx of positively charged ions. Norepinephrine binds to the beta–1 receptor. High blood pressure medications are used to so reduce the heart rate. Parasympathetic stimulation originates from the cardioinhibitory region with impulses traveling via the vagus nerve; the vagus nerve sends branches to both the SA and AV nodes, to portions of both the atria and ventricles. Parasympathetic stimulation releases the neurotransmitter acetylcholine at the neuromuscular junction. ACh slows HR by opening chemical- or ligand-gated potassium ion channels to slow the rate of spontaneous depolarization, which extends repolarization and increases the time before the next spontaneous depolarization occurs.
Without any nervous stimulation, the SA node would establish a sinus rhythm of 100 bpm. Since resting rates are less than this, it becomes evident that parasympathetic stimulation slows HR; this is similar to an individual driving a car with one foot on the brake pedal. To speed up, one need remove one’s foot from the brake and let the engine increase speed. In the case of the heart, decreasing parasympathetic stimulation decreases the release of ACh, which allows HR to increase up to 100 bpm. Any increases beyond this rate would require sympathetic stimulation; the cardiovascular centres receive input from a series of visceral receptors with impulses traveling through visceral sensory fibers within the vagus and sympath
Parthenogenesis is a natural form of asexual reproduction in which growth and development of embryos occur without fertilization. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants parthenogenesis is a component process of apomixis. Parthenogenesis occurs in some plants, some invertebrate animal species and a few vertebrates; this type of reproduction has been induced artificially in a few species including fish and amphibians. Normal egg cells form after meiosis and are haploid, with half as many chromosomes as their mother's body cells. Haploid individuals, are non-viable, parthenogenetic offspring have the diploid chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anywhere between all and half of the mother's alleles; the offspring having all of the mother's genetic material are called full clones and those having only half are called half clones. Full clones are formed without meiosis.
If meiosis occurs, the offspring will get only a fraction of the mother's alleles since crossing over of DNA takes place during meiosis, creating variation. Parthenogenetic offspring in species that use either the XY or the X0 sex-determination system have two X chromosomes and are female. In species that use the ZW sex-determination system, they have either two Z chromosomes or two W chromosomes, or they could have one Z and one W chromosome; some species reproduce by parthenogenesis, while others can switch between sexual reproduction and parthenogenesis. This is called facultative parthenogenesis; the switch between sexuality and parthenogenesis in such species may be triggered by the season, or by a lack of males or by conditions that favour rapid population growth. In these species asexual reproduction occurs either in summer or as long as conditions are favourable; this is because in asexual reproduction a successful genotype can spread without being modified by sex or wasting resources on male offspring who won't give birth.
In times of stress, offspring produced by sexual reproduction may be fitter as they have new beneficial gene combinations. In addition, sexual reproduction provides the benefit of meiotic recombination between non-sister chromosomes, a process associated with repair of DNA double-strand breaks and other DNA damages that may be induced by stressful conditions. Many taxa with heterogony have within them species that have lost the sexual phase and are now asexual. Many other cases of obligate parthenogenesis are found among polyploids and hybrids where the chromosomes cannot pair for meiosis; the production of female offspring by parthenogenesis is referred to as thelytoky while the production of males by parthenogenesis is referred to as arrhenotoky. When unfertilized eggs develop into both males and females, the phenomenon is called deuterotoky. Parthenogenesis can occur without meiosis through mitotic oogenesis; this is called apomictic parthenogenesis. Mature egg cells are produced by mitotic divisions, these cells directly develop into embryos.
In flowering plants, cells of the gametophyte can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother. Examples include aphids. Parthenogenesis involving meiosis is more complicated. In some cases, the offspring are haploid. In other cases, collectively called automictic parthenogenesis, the ploidy is restored to diploidy by various means; this is. In automictic parthenogenesis, the offspring differ from their mother, they are called half clones of their mother. Automixis is a term. Diploidy might be restored by the doubling of the chromosomes without cell division before meiosis begins or after meiosis is completed; this is referred to as an endomitotic cycle. This may happen by the fusion of the first two blastomeres. Other species restore their ploidy by the fusion of the meiotic products; the chromosomes may not separate at one of the two anaphases or the nuclei produced may fuse or one of the polar bodies may fuse with the egg cell at some stage during its maturation.
Some authors consider all forms of automixis sexual. Many others classify the endomitotic variants as asexual and consider the resulting embryos parthenogenetic. Among these authors, the threshold for classifying automixis as a sexual process depends on when the products of anaphase I or of anaphase II are joined together; the criterion for "sexuality" varies from all cases of restitutional meiosis, to those where the nuclei fuse or to only those where gametes are mature at the time of fusion. Those cases of automixis that are classified as sexual reproduction are compared to self-fertilization in their mechanism and consequences; the genetic composition of the offspring depends on. When endomitosis occurs before meiosis or when central fusion occurs, the offspring get all to mor
Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that survive as external parasites of mammals and birds. Fleas live from their hosts. Adult fleas grow to about 3 mm or.12 in long, are brown, have bodies that are "flattened" sideways, or narrow, enabling them to move through their host's fur or feathers. They have strong claws preventing them from being dislodged, they are able to leap a distance of some 50 times their body length, a feat second only to jumps made by another group of insects, the superfamily of froghoppers. Fleas' larvae are worm-like with no limbs; the Siphonaptera are most related to the snow scorpionflies, or snow fleas in the UK, formally the Boreidae, placing them within the Endopterygote insect order Mecoptera. Fleas arose in the early Cretaceous, most as ectoparasites of mammals, before moving on to other groups including birds; each species of flea is more or less a specialist with respect to its host animal species: many species never breed on any other host, though some are less selective.
Some families of fleas are exclusive to a single host group. The oriental rat flea, Xenopsylla cheopis, is a vector of Yersinia pestis, the bacterium which causes bubonic plague; the disease was spread by rodents such as the black rat, which were bitten by fleas that infected humans. Major outbreaks included the Plague of Justinian, c. 540 and the Black Death, c. 1350, both of which killed a sizeable fraction of the world's population. Fleas appear in human culture in such diverse forms as flea circuses, poems like John Donne's erotic The Flea, works of music such as by Modest Mussorgsky, a film by Charlie Chaplin. Fleas are wingless insects, 1/16 to 1/8-inch long, that are agile dark colored, with a proboscis, or stylet, adapted to feeding by piercing the skin and sucking their host's blood through their epipharynx. Flea legs end in strong claws. Unlike other insects, fleas do not possess compound eyes but instead only have simple eyespots with a single biconvex lens, their bodies are laterally compressed, permitting easy movement through the hairs or feathers on the host's body.
The flea body is covered with hard plates called sclerites. These sclerites are covered with many hairs and short spines directed backward, which assist its movements on the host; the tough body is able to withstand great pressure an adaptation to survive attempts to eliminate them by scratching. Fleas lay tiny, oval eggs; the larvae are small and pale, have bristles covering their worm-like bodies, lack eyes, have mouth parts adapted to chewing. The larvae feed on organic matter the feces of mature fleas, which contain dried blood. Adults feed only on fresh blood, their legs are long, the hind pair well adapted for jumping. The flea jump is so rapid and forceful that it exceeds the capabilities of muscle, instead of relying on direct muscle power, fleas store muscle energy in a pad of the elastic protein named resilin before releasing it rapidly. Before the jump, muscles contract and deform the resilin pad storing energy which can be released rapidly to power leg extension for propulsion. To prevent premature release of energy or motions of the leg, the flea employs a "catch mechanism".
Early in the jump, the tendon of the primary jumping muscle passes behind the coxa-trochanter joint, generating a torque which holds the joint closed with the leg close to the body. To trigger jumping, another muscle pulls the tendon forward until it passes the joint axis, generating the opposite torque to extend the leg and power the jump by release of stored energy; the actual take off has been shown by high-speed video to be from the tibiae and tarsi rather than from the trochantera. Fleas are holometabolous insects, going through the four lifecycle stages of egg, larva and imago. In most species, neither female nor male fleas are mature when they first emerge but must feed on blood before they become capable of reproduction; the first blood meal triggers the maturation of the ovaries in females and the dissolution of the testicular plug in males, copulation soon follows. Some species breed all year round while others synchronise their activities with their hosts' life cycles or with local environmental factors and climatic conditions.
Flea populations consist of 50% eggs, 35% larvae, 10% pupae, 5% adults. The number of eggs laid depends with batch sizes ranging from two to several dozen; the total number of eggs produced in a female's lifetime varies from around one hundred to several thousand. In some species, the flea lives in the nest or burrow and the eggs are deposited on the substrate, but in others, the eggs are laid on the host itself and can fall off onto the ground; because of this, areas where the host rests and sleeps become one of the primary habitats of eggs and developing larvae. The eggs take around two days to two weeks to hatch. Experiments have show
A microscope is an instrument used to see objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small structures using such an instrument. Microscopic means invisible to the eye. There are many types of microscopes, they may be grouped in different ways. One way is to describe the way the instruments interact with a sample to create images, either by sending a beam of light or electrons to a sample in its optical path, or by scanning across, a short distance from the surface of a sample using a probe; the most common microscope is the optical microscope, which uses light to pass through a sample to produce an image. Other major types of microscopes are the fluorescence microscope, the electron microscope and the various types of scanning probe microscopes. Although objects resembling lenses date back 4000 years and there are Greek accounts of the optical properties of water-filled spheres followed by many centuries of writings on optics, the earliest known use of simple microscopes dates back to the widespread use of lenses in eyeglasses in the 13th century.
The earliest known examples of compound microscopes, which combine an objective lens near the specimen with an eyepiece to view a real image, appeared in Europe around 1620. The inventor is unknown. Several revolve around the spectacle-making centers in the Netherlands including claims it was invented in 1590 by Zacharias Janssen and/or Zacharias' father, Hans Martens, claims it was invented by their neighbor and rival spectacle maker, Hans Lippershey, claims it was invented by expatriate Cornelis Drebbel, noted to have a version in London in 1619. Galileo Galilei seems to have found after 1610 that he could close focus his telescope to view small objects and, after seeing a compound microscope built by Drebbel exhibited in Rome in 1624, built his own improved version. Giovanni Faber coined the name microscope for the compound microscope Galileo submitted to the Accademia dei Lincei in 1625; the first detailed account of the microscopic anatomy of organic tissue based on the use of a microscope did not appear until 1644, in Giambattista Odierna's L'occhio della mosca, or The Fly's Eye.
The microscope was still a novelty until the 1660s and 1670s when naturalists in Italy, the Netherlands and England began using them to study biology. Italian scientist Marcello Malpighi, called the father of histology by some historians of biology, began his analysis of biological structures with the lungs. Robert Hooke's Micrographia had a huge impact because of its impressive illustrations. A significant contribution came from Antonie van Leeuwenhoek who achieved up to 300 times magnification using a simple single lens microscope, he sandwiched a small glass ball lens between the holes in two metal plates riveted together, with an adjustable-by-screws needle attached to mount the specimen. Van Leeuwenhoek re-discovered red blood cells and spermatozoa, helped popularise the use of microscopes to view biological ultrastructure. On 9 October 1676, van Leeuwenhoek reported the discovery of micro-organisms; the performance of a light microscope depends on the quality and correct use of the condensor lens system to focus light on the specimen and the objective lens to capture the light from the specimen and form an image.
Early instruments were limited until this principle was appreciated and developed from the late 19th to early 20th century, until electric lamps were available as light sources. In 1893 August Köhler developed a key principle of sample illumination, Köhler illumination, central to achieving the theoretical limits of resolution for the light microscope; this method of sample illumination produces lighting and overcomes the limited contrast and resolution imposed by early techniques of sample illumination. Further developments in sample illumination came from the discovery of phase contrast by Frits Zernike in 1953, differential interference contrast illumination by Georges Nomarski in 1955. In the early 20th century a significant alternative to the light microscope was developed, an instrument that uses a beam of electrons rather than light to generate an image; the German physicist, Ernst Ruska, working with electrical engineer Max Knoll, developed the first prototype electron microscope in 1931, a transmission electron microscope.
The transmission electron microscope works on similar principles to an optical microscope but uses electrons in the place of light and electromagnets in the place of glass lenses. Use of electrons, instead of light, allows for much higher resolution. Development of the transmission electron microscope was followed in 1935 by the development of the scanning electron microscope by Max Knoll. Although TEMs were being used for research before WWII, became popular afterwards, the SEM was not commercially available until 1965. Transmission electron microscopes became popular following the Second World War. Ernst Ruska, working at Siemens, developed the first commercial transmission electron microscope and, in the 1950s, major scientific conferences on electron microscopy started being held. In 1965, the first commercial scanning electron microscope was developed by Profess
Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, sponges, baleen whales, many fish; some birds, such as flamingos and certain species of duck, are filter feeders. Filter feeders can play an important role in clarifying water, are therefore considered ecosystem engineers, they are important in bioaccumulation and, as a result, as indicator organisms. Most forage fish are filter feeders. For example, the Atlantic menhaden, a type of herring, lives on plankton caught in midwater. Adult menhaden can filter up to four gallons of water a minute and play an important role in clarifying ocean water, they are a natural check to the deadly red tide. In addition to these bony fish, four types of cartilaginous fishes are filter feeders; the whale shark sucks in a mouthful of water, closes its mouth and expels the water through its gills.
During the slight delay between closing the mouth and opening the gill flaps, plankton is trapped against the dermal denticles which line its gill plates and pharynx. This fine sieve-like apparatus, a unique modification of the gill rakers, prevents the passage of anything but fluid out through the gills. Any material caught in the filter between the gill bars is swallowed. Whale sharks have been observed "coughing" and it is presumed that this is a method of clearing a build up of food particles in the gill rakers; the megamouth shark has luminous organs called photophores around its mouth. It is believed they may exist to lure small fish into its mouth; the basking shark is a passive filter feeder, filtering zooplankton, small fish, invertebrates from up to 2,000 tons of water per hour. Unlike the megamouth and whale sharks, the basking shark does not appear to seek its quarry. Unlike the other large filter feeders, it relies only on the water, pushed through the gills by swimming. Manta rays can time their arrival at the spawning of large shoals of fish and feed on the free-floating eggs and sperm.
This stratagem is employed by whale sharks. Mysidacea are small crustaceans that live close to shore and hover above the sea floor collecting particles with their filter basket, they are an important food source for herring, cod and striped bass. Mysids have a high resistance to toxins in polluted areas, may contribute to high toxin levels in their predators. Antarctic krill manages to directly utilize the minute phytoplankton cells, which no other higher animal of krill size can do; this is accomplished through filter feeding, using the krill's developed front legs, providing for a efficient filtering apparatus: the six thoracopods form a effective "feeding basket" used to collect phytoplankton from the open water. In the animation at the top of this page, the krill is hovering at a 55° angle on the spot. In lower food concentrations, the feeding basket is pushed through the water for over half a meter in an opened position, the algae are combed to the mouth opening with special setae on the inner side of the thoracopods.
Porcelain crabs have feeding appendages covered with setae to filter food particles from the flowing water. Most species of barnacles are filter feeders, using their modified legs to sift plankton from the water; the baleen whales, one of two suborders of the Cetacea, are characterized by having baleen plates for filtering food from water, rather than teeth. This distinguishes them from the other suborder of the toothed whales; the suborder contains fourteen species. Baleen whales seek out a concentration of zooplakton, swim through it, either open-mouthed or gulping, filter the prey from the water using their baleens. A baleen is a row of a large number of keratin plates attached to the upper jaw with a composition similar to those in human hair or fingernails; these plates are triangular in section with the largest, inward-facing side bearing fine hairs forming a filtering mat. Right whales are slow swimmers with large mouths, their baleen plates are narrow and long — up to 4 m in bowheads — and accommodated inside the enlarged lower lip which fits onto the bowed upper jaw.
As the right whale swims, a front gap between the two rows of baleen plates lets the water in together with the prey, while the baleens filter out the water. Rorquals such as the blue whale, in contrast, have smaller heads, are fast swimmers with short and broad baleen plates. To catch prey, they open their lower jaw — 90° — swim through a swarm gulping, while lowering their tongue so that the head's ventral grooves expand and vastly increase the amount of water taken in. Baleen whales eat krill in polar or subpolar waters during summers, but can take schooling fish in the Northern Hemisphere. All baleen whales except the gray whale feed near the water surface diving deeper than 100 m or for extended periods. Gray whales live in shallow waters feeding on bottom-living organisms such as amphipods. Bivalves are aquatic molluscs. Both shells are symmetrical along the hinge line; the class has 30,000 species, including scallops, clams and mussels. Most bivalves are filter feeders, extracting organic matter