An aquatic animal is an animal, either vertebrate or invertebrate, which lives in the water for most or all of its lifetime. Many insects such as mosquitoes, mayflies and caddisflies have aquatic larvae, with winged adults. Aquatic animals may breathe air or extract oxygen that dissolved in water through specialised organs called gills, or directly through the skin. Natural environments and the animals that live in them can be categorized as terrestrial; this designation is paraphyletic. The term aquatic can be applied to animals that live in either fresh salt water. However, the adjective marine is most used for animals that live in saltwater, i.e. in oceans, etc. Aquatic animals are of special concern to conservationists because of the fragility of their environments. Aquatic animals are subject to pressure from overfishing, destructive fishing, marine pollution and climate change. In addition to water breathing animals, e.g. fish, most mollusks etc. the term "aquatic animal" can be applied to air-breathing aquatic or sea mammals such as those in the orders Cetacea and Sirenia, which cannot survive on land, as well as the pinnipeds.
The term "aquatic mammal" is applied to four-footed mammals like the river otter and beavers, although these are technically amphibious or semiaquatic. Amphibians, like frogs, while requiring water, are separated into their own environmental classification; the majority of amphibians have an aquatic larval stage, like a tadpole, but live as terrestrial adults, may return to the water to mate. Certain fish evolved to breathe air to survive oxygen-deprived water, such as Arapaima and walking catfish. Most mollusks have gills, while some fresh water ones have a lung instead and some amphibious ones have both. "Annelids." Nonindigenous Aquatic Species. Web. 2 May 2012. <https://web.archive.org/web/20120606154809/http://nas.er.usgs.gov/taxgroup/annelids/>. National Invasive Species Information Center. Web. 2 May 2012. <http://www.invasivespeciesinfo.gov/aquatics/main.shtml>
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
Binomial nomenclature called binominal nomenclature or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomen, binominal name or a scientific name; the first part of the name – the generic name – identifies the genus to which the species belongs, while the second part – the specific name or specific epithet – identifies the species within the genus. For example, humans belong within this genus to the species Homo sapiens. Tyrannosaurus rex is the most known binomial; the formal introduction of this system of naming species is credited to Carl Linnaeus beginning with his work Species Plantarum in 1753. But Gaspard Bauhin, in as early as 1623, had introduced in his book Pinax theatri botanici many names of genera that were adopted by Linnaeus; the application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature for animals and the International Code of Nomenclature for algae and plants.
Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences, both in the terminology they use and in their precise rules. In modern usage, the first letter of the first part of the name, the genus, is always capitalized in writing, while that of the second part is not when derived from a proper noun such as the name of a person or place. Both parts are italicized when a binomial name occurs in normal text, thus the binomial name of the annual phlox is now written as Phlox drummondii. In scientific works, the authority for a binomial name is given, at least when it is first mentioned, the date of publication may be specified. In zoology "Patella vulgata Linnaeus, 1758"; the name "Linnaeus" tells the reader who it was that first published a description and name for this species of limpet. "Passer domesticus". The original name given by Linnaeus was Fringilla domestica; the ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, although nomenclatorial catalogs include such information.
In botany "Amaranthus retroflexus L." – "L." is the standard abbreviation used in botany for "Linnaeus". "Hyacinthoides italica Rothm. – Linnaeus first named this bluebell species Scilla italica. The name is composed of two word-forming elements: "bi", a Latin prefix for two, "-nomial", relating to a term or terms; the word "binomium" was used in Medieval Latin to mean a two-term expression in mathematics. Prior to the adoption of the modern binomial system of naming species, a scientific name consisted of a generic name combined with a specific name, from one to several words long. Together they formed a system of polynomial nomenclature; these names had two separate functions. First, to designate or label the species, second, to be a diagnosis or description. In a simple genus, containing only two species, it was easy to tell them apart with a one-word genus and a one-word specific name; such "polynomial names" may sometimes look like binomials, but are different. For example, Gerard's herbal describes various kinds of spiderwort: "The first is called Phalangium ramosum, Branched Spiderwort.
The other... is aptly termed Phalangium Ephemerum Virginianum, Soon-Fading Spiderwort of Virginia". The Latin phrases are short descriptions, rather than identifying labels; the Bauhins, in particular Caspar Bauhin, took some important steps towards the binomial system, by pruning the Latin descriptions, in many cases to two words. The adoption by biologists of a system of binomial nomenclature is due to Swedish botanist and physician Carl von Linné, more known by his Latinized name Carl Linnaeus, it was in his 1753 Species Plantarum that he first began using a one-word "trivial name" together with a generic name in a system of binomial nomenclature. This trivial name is what is now known as specific name; the Bauhins' genus names were retained in many of these, but the descriptive part was reduced to a single word. Linnaeus's trivial names introduced an important new idea, namely that the function of a name could be to give a species a unique label; this meant. Thus Gerard's Phalangium ephemerum virginianum became Tradescantia virgi
Mollusca is the second largest phylum of invertebrate animals. The members are known as mollusks. Around 85,000 extant species of molluscs are recognized; the number of fossil species is estimated between 100,000 additional species. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs live in freshwater and terrestrial habitats, they are diverse, not just in size and in anatomical structure, but in behaviour and in habitat. The phylum is divided into 8 or 9 taxonomic classes, of which two are extinct. Cephalopod molluscs, such as squid and octopus, are among the most neurologically advanced of all invertebrates—and either the giant squid or the colossal squid is the largest known invertebrate species; the gastropods are by far the most numerous molluscs and account for 80% of the total classified species. The three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula, the structure of the nervous system.
Other than these common elements, molluscs express great morphological diversity, so many textbooks base their descriptions on a "hypothetical ancestral mollusc". This has a single, "limpet-like" shell on top, made of proteins and chitin reinforced with calcium carbonate, is secreted by a mantle covering the whole upper surface; the underside of the animal consists of a single muscular "foot". Although molluscs are coelomates, the coelom tends to be small; the main body cavity is a hemocoel. The "generalized" mollusc's feeding system consists of a rasping "tongue", the radula, a complex digestive system in which exuded mucus and microscopic, muscle-powered "hairs" called cilia play various important roles; the generalized mollusc has three in bivalves. The brain, in species that have one, encircles the esophagus. Most molluscs have eyes, all have sensors to detect chemicals and touch; the simplest type of molluscan reproductive system relies on external fertilization, but more complex variations occur.
All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults. The coelomic cavity is reduced, they have kidney-like organs for excretion. Good evidence exists for the appearance of gastropods and bivalves in the Cambrian period, 541 to 485.4 million years ago. However, the evolutionary history both of molluscs' emergence from the ancestral Lophotrochozoa and of their diversification into the well-known living and fossil forms are still subjects of vigorous debate among scientists. Molluscs still are an important food source for anatomically modern humans. There is a risk of food poisoning from toxins which can accumulate in certain molluscs under specific conditions and because of this, many countries have regulations to reduce this risk. Molluscs have, for centuries been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye, sea silk, their shells have been used as money in some preindustrial societies. Mollusc species can represent hazards or pests for human activities.
The bite of the blue-ringed octopus is fatal, that of Octopus apollyon causes inflammation that can last for over a month. Stings from a few species of large tropical cone shells can kill, but their sophisticated, though produced, venoms have become important tools in neurological research. Schistosomiasis is transmitted to humans via water snail hosts, affects about 200 million people. Snails and slugs can be serious agricultural pests, accidental or deliberate introduction of some snail species into new environments has damaged some ecosystems; the words mollusc and mollusk are both derived from the French mollusque, which originated from the Latin molluscus, from mollis, soft. Molluscus was itself an adaptation of Aristotle's τὰ μαλάκια ta malákia, which he applied inter alia to cuttlefish; the scientific study of molluscs is accordingly called malacology. The name Molluscoida was used to denote a division of the animal kingdom containing the brachiopods and tunicates, the members of the three groups having been supposed to somewhat resemble the molluscs.
As it is now known these groups have no relation to molluscs, little to one another, the name Molluscoida has been abandoned. The most universal features of the body structure of molluscs are a mantle with a significant cavity used for breathing and excretion, the organization of the nervous system. Many have a calcareous shell. Molluscs have developed such a varied range of body structures, it is difficult to find synapomorphies to apply to all modern groups; the most general characteristic of molluscs is they are bilaterally symmetrical. The following are present in all modern molluscs: The dorsal part of the body wall is a mantle which secretes calcareous spicules, plates or shells, it overlaps the body with enough spare room to form a mantle cavity. The anus and genitals open into the mantle cavity. There are two pairs of main nerve cords. Other characteristics that appear in textbooks have significant exceptions: Estimates of accepted described living species of molluscs vary from 50,000 to a maximum of 120,000 species.
In 1969 David Nicol estimated the probable total number of living mollusc species at 107,000 of which were ab
Unionida is a monophyletic order of freshwater mussels, aquatic bivalve molluscs. The order includes most including the freshwater pearl mussels; the most common families are the Margaritiferidae. All have in common a larval stage, temporarily parasitic on fish, nacreous shells, high in organic matter, that may crack upon drying out, siphons too short to permit the animal to live buried in sediment; the shells of these mussels are variable in shape, but equivalve and elongate. They have solid, nacreous valves with a pearly interior, radial sculpture, an entire pallial line. Families and species in the order Unionida are found on six continents, where they are restricted to freshwater rivers, streams and some lakes. There are 900 species worldwide. Around 300 species of these freshwater mussels are endemic to North America. Unlike other bivalve orders, Unionida has no marine species, although one species tolerates brackish water; this widespread trait and its global distribution suggests the group has inhabited freshwater throughout its geologic history.
Unionida burrow into the substrate in clean, fast flowing freshwater water rivers and creeks, with their posterior margins exposed. They pump water through the incurrent aperture, obtaining oxygen and filtering food from the water column. Freshwater mussels are some of the longest-living invertebrates in existence; these clams have, like all bivalve mollusks, a shell consisting of two parts that are hinged together, which can be closed to protect the animal's soft body within. Like all mollusks, the freshwater mussels have a muscular "foot", which enables the mussel to move and bury itself within the bottom substrate of its freshwater habitat. Unionida have a complex life cycle involving parasitic larvae; this larval form used to be described as "parasitic worms" on the fish host, the larvae are not "worms" and do not harm fish under normal circumstances. Most of these freshwater mussel species have separate sexes; the sperm is ejected from the mantle cavity through the male's excurrent aperture and taken into the female's mantle cavity through the incurrent aperture.
Fertilised eggs move from the gonads to the gills where they further ripen and metamorph into glochidia, the first larval stage. Mature glochidia are released by the female and attach to the gills, fins or skin of a host fish; the freshwater mussel larvae have hooks, which enable the individual to attach itself to fish. Some freshwater mussels release their glochidia in mucilaginous packets called conglutinates; the conglutinate has a sticky filament that allows it to adhere to the substrate so it is not washed away. There is an more specialized way of dispersal known as a super-conglutinate; the super-conglutinate resembles an aquatic fly larva or a fish egg, complete with a dark area that looks like an eyespot, it is appetizing to fish. When a fish consumes it, it breaks up. Mussels that produce conglutinates and super-conglutinates are gill parasites, the glochidia attaching to the fish gills to continue their development into juveniles. A cyst is formed around the glochidia, they stay on the fish for several weeks or months before they fall off as juvenile freshwater mussels which bury themselves in the sediment.
This unique life cycle allows Unionida freshwater mussels to move upstream with the fish host species. Many of these freshwater mussel species face conservation issues due to habitat degradation and in some cases due to over-exploitation for the freshwater pearl industry, for the nacre of their shells, used in button manufacturing. Of the North American Unionida about 70% are either extinct, threatened or are listed as species of special concern; these bivalve mollusks were exploited for freshwater pearls, for their nacre, used in the button manufacturing industry in the late 19th and early 20th centuries. The effects of heavy fishing for freshwater mussels in North America in for use in manufacturing buttons put many of these species close to extinction; the "pearl rush" in North America occurred in the mid to late 1800s as people could find freshwater mussels in rivers and streams by "pollywogging" for mussels, some of which had freshwater pearls which they could sell for a significant price.
The art of "pollywogging" involves shuffling one's feet in the mud feeling around for freshwater mussels. Because this was easy to do, an easy way to make money from freshwater selling pearls, this period has been euphemistically called the "pearl rush", some historians have compared it to the gold rush in California. A formal freshwater mussel fishing industry was established in the mid-1850s to take advantage of this natural resource; the "pearl rush" to find freshwater pearls became so intense in some rivers that millions of freshwater mussels were killed in a few years. In some rivers and streams entire freshwater mussel beds were eliminated. Although the negative impact of the "pearl rush" on freshwater mussel populations was significant, in the cold light of history it was minor compared to the over fishing that took place just a few years with the "pearl" button industry. Freshwater pearls from North America come from freshwater mussels in the family Unionidae. About 20 different species of Unionidae are commercially harvested for pearls.
The common names of the most prolific pearl-bearing species include: the
The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve mollusks sometimes known as river mussels, or as unionids. The range of distribution for this family is world-wide, it is at its most diverse in North America, with about 297 recognised taxa, but China and Southeast Asia support diverse faunas. Freshwater mussels occupy a wide range of habitats, but most occupy lotic waters, i.e. flowing water such as rivers and creeks. The recent phylogenetic study reveals that the Unionidae most originated in Southeast and East Asia in the Jurassic, with the earliest expansions into North America and Africa following the colonization of Europe and India. Unionidae burrow with their posterior margins exposed, they pump water through the incurrent aperture, obtaining food. They remove phytoplankton and zooplankton, as well as suspended bacteria, fungal spores, dissolved organic matter. Despite extensive laboratory studies, which of these filtrates unionoids process remains uncertain.
In high densities, they have the ability to influence water clarity but filtration rates are dependent on water temperature, current velocity, particle size and concentration. In addition, gill morphology can determine particle size filtered, as well as the rate. Unionidae are distinguished by a complex lifecycle. Most unionids are of separate sex, although some species, such as Elliptio complanata, are known to be hermaphroditic; the sperm is ejected from the mantle cavity through the male’s excurrent aperture and taken into the female's mantle cavity through the incurrent aperture. Fertilised eggs move from the gonads to the gills where they further ripen and metamorph into glochidia, the first larval stage. Mature glochidia are released by the female and attach to the gills, fins, or skin of a host fish. A cyst is formed around the glochidia, they stay on the fish for several weeks or months before they fall off as juvenile mussels, which bury themselves in the sediment; some of the species in the Unionidae known as pocketbook mussels, have evolved a remarkable reproductive strategy.
The edge of the female's body that protrudes from the valves of the shell develops into an imitation of a small fish complete with markings and false eyes. This decoy attracts the attention of real fish; some fish see the decoy as prey. Whatever they see, they approach for a closer look and the mussel releases huge numbers of larvae from her gills, dousing the inquisitive fish with her tiny, parasitic young; these glochidial larvae are drawn into the fish's gills, where they attach and trigger a tissue response that forms a small cyst in which the young mussel resides. It feeds by digesting the tissue of the fish within the cyst. Sex is determined by a region located on the mitochondrial DNA, the male open-reading frame and female open-reading frame. Hermaphroditic mussels lack these regions and contain a female-like open-reading frame dubbed hermaphroditic open-reading frame. In many mussels, the hermaphroditic state is ancestral and the male sex evolved later; this region of the mitochondria may be responsible for the evolution of doubly uniparental inheritance seen in freshwater mussels.
In large enough quantities, unionid shells can have enough of an impact on environmental conditions to affect the ability of organic remains in the local environment to fossilize. For example, in the Dinosaur Park Formation, fossil hadrosaur eggshell is rare because the breakdown of tannins from local coniferous vegetation would have caused the ancient waters to become acidic. Eggshell fragments are present in only two microfossil sites, both of which are dominated by the preserved shells of invertebrate life, including unionids; the slow dissolution of these shells releasing calcium carbonate into the water raised the water's pH high enough to prevent the eggshell fragments from dissolving before they could be fossilized. Missouri State Unio Gallery Freshwater Mollusk Conservation Society Ohio State University: Division of Molluscs - Freshwater Mussel Collection - Unionidae Unionidae at The MUSSEL Project Web Site
Freshwater bivalves are one kind of freshwater molluscs, along with freshwater snails. They are bivalves which live in freshwater, as opposed to saltwater, the main habitat type for bivalves; the majority of species of bivalve molluscs live in the sea, but in addition, a number of different families live in freshwater. These families belong to two different evolutionary lineages, the two groups are not related. Freshwater bivalves live in many types of habitat, ranging from small ditches and ponds, to lakes, canals and swamps. Species in the two groups vary in size; some of the pea clams have an adult size of only 3 mm. In contrast, one of the largest species of freshwater bivalves is the swan mussel, in the family Unionidae. Freshwater pearl mussels are economically important as a source of freshwater pearls and mother of pearl. Order Unionida The Unionida, of worldwide distribution, are the pearly freshwater mussels. All reproduce by means of a larval stage, parasitic on a fish or salamander. Many species are utilized as sources of mother-of-pearl.
Families: Margaritiferidae Unionidae Hyriidae Etheriidae Mutelidae Mycetopodidae IridinidaeOrder Unionida: pearly freshwater mussels Order Veneroida The Veneroida is a large group of bivalve "clams", most of which are marine. However, several families occur in brackish waters. Families: Corbiculidae Sphaeriidae Dreissenidae Order Veneroida ANSP site Info on Unionida genera at Info on Rhode Island freshwater clams and mussels