128-417: In zoology , a tentacle is a flexible, mobile, and elongated organ present in some species of animals , most of them invertebrates . In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work mainly like muscular hydrostats . Most forms of tentacles are used for grasping and feeding. Many are sensory organs , variously receptive to touch , vision , or to
256-618: A coelom , an internal cavity lined by mesothelium . Some encrusting bryozoan colonies with mineralized exoskeletons look very like small corals. However, bryozoan colonies are founded by an ancestrula, which is round rather than shaped like a normal zooid of that species. On the other hand, the founding polyp of a coral has a shape like that of its daughter polyps, and coral zooids have no coelom or lophophore . Entoprocts , another phylum of filter-feeders, look rather like bryozoans but their lophophore -like feeding structure has solid tentacles, their anus lies inside rather than outside
384-741: A dasyclad alga. Early fossils are mainly of erect forms, but encrusting forms gradually became dominant. It is uncertain whether the phylum is monophyletic . Bryozoans' evolutionary relationships to other phyla are also unclear, partly because scientists' view of the family tree of animals is mainly influenced by better-known phyla. Both morphological and molecular phylogeny analyses disagree over bryozoans' relationships with entoprocts, about whether bryozoans should be grouped with brachiopods and phoronids in Lophophorata , and whether bryozoans should be considered protostomes or deuterostomes . Bryozoans, phoronids and brachiopods strain food out of
512-425: A "crown" of tentacles, the name "Bryozoa" was promoted to phylum level to include the two classes Ectoprocta and Entoprocta. However, in 1869 Hinrich Nitsche regarded the two groups as quite distinct for a variety of reasons, and coined the name "Ectoprocta" for Ehrenberg's "Bryozoa". Despite their apparently similar methods of feeding, they differed markedly anatomically; in addition to the different positions of
640-436: A bryozoan. The analysis also concluded that the classes Phylactolaemata, Stenolaemata and Gymnolaemata are also monophyletic, but could not determine whether Stenolaemata are more closely related to Phylactolaemata or Gymnolaemata . The Gymnolaemata are traditionally divided into the soft-bodied Ctenostomatida and mineralized Cheilostomata, but the 2009 analysis considered it more likely that neither of these orders
768-500: A colony because there are so few gonozooids in one colony. The aperture in gonozooids, which is called an ooeciopore, acts as a point for larvae to exit. Some gonozooids have very complex shapes with autozooidal tubes passing through chambers within them. All larvae released from a gonozooid are clones created by division of a single egg; this is called monozygotic polyembryony , and is a reproductive strategy also used by armadillos . Cheilostome bryozoans also brood their embryos; one of
896-451: A combination of zooids that are in their male and female stages. All species emit sperm into the water. Some also release ova into the water, while others capture sperm via their tentacles to fertilize their ova internally. In some species the larvae have large yolks , go to feed, and quickly settle on a surface. Others produce larvae that have little yolk but swim and feed for a few days before settling. After settling, all larvae undergo
1024-517: A fast-growing invasive bryozoan off the northeast and northwest coasts of the US, has reduced kelp forests so much that it has affected local fish and invertebrate populations. Bryozoans have spread diseases to fish farms and fishermen. Chemicals extracted from a marine bryozoan species have been investigated for treatment of cancer and Alzheimer's disease , but analyses have not been encouraging. Mineralized skeletons of bryozoans first appear in rocks from
1152-403: A flexible membrane that replaces part of the exoskeleton, and transverse muscles anchored on the far side of the exoskeleton increase the fluid pressure by pulling the membrane inwards. In others there is no gap in the protective skeleton, and the transverse muscles pull on a flexible sac which is connected to the water outside by a small pore; the expansion of the sac increases the pressure inside
1280-402: A flexible tube called the "invert", which can be turned inside-out and withdrawn into the polypide, rather like the finger of a rubber glove; in this position the lophophore lies inside the invert and is folded like the spokes of an umbrella. The invert is withdrawn, sometimes within 60 milliseconds , by a pair of retractor muscles that are anchored at the far end of the cystid. Sensors at
1408-601: A laboratory setting. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection . In one sense, the first modern ethologist was Charles Darwin , whose book, The Expression of the Emotions in Man and Animals , influenced many future ethologists. A subfield of ethology is behavioral ecology which attempts to answer Nikolaas Tinbergen 's four questions with regard to animal behavior: what are
SECTION 10
#17328511886811536-454: A major source of the carbonate minerals that make up limestones, and their fossils are incredibly common in marine sediments worldwide from the Ordovician onward. However, unlike corals and other colonial animals found in the fossil record, Bryozoan colonies did not reach large sizes. Fossil bryozoan colonies are typically found highly fragmented and scattered; the preservation of complete zoaria
1664-457: A new dent becomes the point from which the gut grows. The ectoproct coelom is formed by neither of the processes used by other bilaterians, enterocoely , in which pouches that form on the wall of the gut become separate cavities, nor schizocoely , in which the tissue between the gut and the body wall splits, forming paired cavities. When entoprocts were discovered in the 19th century, they and bryozoans (ectoprocts) were regarded as classes within
1792-413: A new footing, by explaining the processes by which it can occur, and providing observational evidence that it had done so. Darwin's theory was rapidly accepted by the scientific community and soon became a central axiom of the rapidly developing science of biology. The basis for modern genetics began with the work of Gregor Mendel on peas in 1865, although the significance of his work was not realized at
1920-406: A new perspective on the fundamental basis of life. Having previously been the realm of gentlemen naturalists, over the 18th, 19th and 20th centuries, zoology became an increasingly professional scientific discipline . Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography, laying
2048-709: A process involving the union of a male and female haploid gamete , each gamete formed by meiosis . Ordinarily, gametes produced by separate individuals unite by a process of fertilization to form a diploid zygote that can then develop into a genetically unique individual progeny. However, some animals are also capable, as an alternative reproductive process, to reproduce parthenogenetically. Parthenogenesis has been described in snakes and lizards (see Misplaced Pages Parthenogenesis in squamates ), in amphibians (see Misplaced Pages Parthenogenesis in amphibians ) and in numerous other species (see Misplaced Pages Parthenogenesis ). Generally, meiosis in parthanogenetically reproducing animals occurs by
2176-627: A radical metamorphosis that destroys and rebuilds almost all the internal tissues. Freshwater species also produce statoblasts that lie dormant until conditions are favorable, which enables a colony's lineage to survive even if severe conditions kill the mother colony. Predators of marine bryozoans include sea slugs (nudibranchs), fish, sea urchins , pycnogonids , crustaceans , mites and starfish . Freshwater bryozoans are preyed on by snails, insects, and fish. In Thailand , many populations of one freshwater species have been wiped out by an introduced species of snail. Membranipora membranacea ,
2304-609: A similar process to that in sexually reproducing animals, but the diploid zygote nucleus is generated by the union of two haploid genomes from the same individual rather than from different individuals. Bryozoa See text . Ectoprocta (Nitsche, 1869) (formerly subphylum of Bryozoa) Bryozoa (also known as the Polyzoa , Ectoprocta or commonly as moss animals ) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies . Typically about 0.5 millimetres ( 1 ⁄ 64 in) long, they have
2432-474: A special feeding structure called a lophophore , a "crown" of tentacles used for filter feeding . Most marine bryozoans live in tropical waters, but a few are found in oceanic trenches and polar waters. The bryozoans are classified as the marine bryozoans (Stenolaemata), freshwater bryozoans (Phylactolaemata), and mostly-marine bryozoans (Gymnolaemata), a few members of which prefer brackish water . 5,869 living species are known. Originally all of
2560-560: A species that is symbiotic with hermit crabs and lives on their shells. These zooids are smaller than the others and have four short tentacles and four long tentacles, unlike the autozooids which have 15–16 tentacles. Androzooids are also found in species with mobile colonies that can crawl around. It is possible that androzooids are used to exchange sperm between colonies when two mobile colonies or bryozoan-encrusted hermit crabs happen to encounter one another. Spinozooids are hollow, movable spines, like very slender, small tubes, present on
2688-455: A type of avicularia, the operculum is modified to form a long bristle that has a wide range of motion. They may function as defenses against predators and invaders, or as cleaners. In some species that form mobile colonies, vibracula around the edges are used as legs for burrowing and walking. Kenozooids (from the Greek kenós 'empty') consist only of the body wall and funicular strands crossing
SECTION 20
#17328511886812816-500: A variety of forms, including fans, bushes and sheets. Single animals, called zooids , live throughout the colony and are not fully independent. These individuals can have unique and diverse functions. All colonies have "autozooids", which are responsible for feeding, excretion , and supplying nutrients to the colony through diverse channels. Some classes have specialist zooids like hatcheries for fertilized eggs, colonial defence structures, and root-like attachment structures. Cheilostomata
2944-438: A variety of functions other than feeding; colony members are genetically identical and co-operate, rather like the organs of larger animals. What type of zooid grows where in a colony is determined by chemical signals from the colony as a whole or sometimes in response to the scent of predators or rival colonies. The bodies of all types have two main parts. The cystid consists of the body wall and whatever type of exoskeleton
3072-417: Is secreted by the epidermis . The exoskeleton may be organic ( chitin , polysaccharide or protein ) or made of the mineral calcium carbonate . The latter is always absent in freshwater species. The body wall consists of the epidermis, basal lamina (a mat of non-cellular material), connective tissue , muscles, and the mesothelium which lines the coelom (main body cavity) – except that in one class,
3200-453: Is a form of scientific taxonomy . Modern biological classification has its root in the work of Carl Linnaeus , who grouped species according to shared physical characteristics. These groupings have since been revised to improve consistency with the Darwinian principle of common descent . Molecular phylogenetics , which uses nucleic acid sequence as data, has driven many recent revisions and
3328-508: Is a layer of helical muscle that helps each tentacle to twist or turn in any direction where the prey is sensed. The modern convention, however, is to speak of appendages as "tentacles" when they have relatively thin " peduncles " or "stalks" with "clubs" at their tips. In contrast the convention refers to the relatively shorter appendages as "arms". By this definition the eight appendages of octopuses, though quite long, count as arms. While arms are distinct from tentacles (a definition specific to
3456-657: Is administered by the International Code of Zoological Nomenclature . A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature, but has yet to be formally adopted. Vertebrate zoology is the biological discipline that consists of the study of vertebrate animals, that is animals with a backbone , such as fish , amphibians , reptiles , birds and mammals . The various taxonomically oriented disciplines i.e. mammalogy , biological anthropology , herpetology , ornithology , and ichthyology seek to identify and classify species and study
3584-507: Is already exhausted. They are formed by patches of non-feeding heterozooids. New chimneys appear near the edges of expanding colonies, at points where the speed of the outflow is already high, and do not change position if the water flow changes. Some freshwater species secrete a mass of gelatinous material, up to 1 m (3 ft 3 in) in diameter, to which the zooids stick. Other freshwater species have plant-like shapes with "trunks" and "branches", which may stand erect or spread over
3712-480: Is an integrative field of study, uniting concepts and information from evolutionary biology , taxonomy , ecology , physical geography , geology , paleontology and climatology . The origin of this field of study is widely accredited to Alfred Russel Wallace , a British biologist who had some of his work jointly published with Charles Darwin . Molecular biology studies the common genetic and developmental mechanisms of animals and plants, attempting to answer
3840-402: Is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Physiology studies how, for example, the nervous , immune , endocrine , respiratory , and circulatory systems function and interact. Developmental biology is the study of
3968-525: Is complex and not completely consistent. Works since 2000 have used various names to resolve the ambiguity, including: "Bryozoa", "Ectoprocta", "Bryozoa (Ectoprocta)", and "Ectoprocta (Bryozoa)". Some have used more than one approach in the same work. The common name "moss animals" is the literal meaning of "Bryozoa", from Greek βρυόν ('moss') and ζῷα ('animals'), based on the mossy appearance of encrusting species. Until 2008 there were "inadequately known and misunderstood type species belonging to
Tentacle - Misplaced Pages Continue
4096-406: Is done on both the microscopic and molecular levels for single-celled organisms such as bacteria as well as the specialized cells in multicellular organisms such as humans . Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are particularly relevant to molecular biology. Anatomy considers
4224-400: Is feasible because the loss of zooids to a single attack is unlikely to be significant. Colonies of some encrusting species also produce special heterozooids to limit the expansion of other encrusting organisms, especially other bryozoans. In some cases this response is more belligerent if the opposition is smaller, which suggests that zooids on the edge of a colony can somehow sense the size of
4352-443: Is likely to continue to do so. Biological classification belongs to the science of zoological systematics . Many scientists now consider the five-kingdom system outdated. Modern alternative classification systems generally start with the three-domain system : Archaea (originally Archaebacteria); Bacteria (originally Eubacteria); Eukaryota (including protists , fungi , plants , and animals ) These domains reflect whether
4480-631: Is monophyletic and that mineralized skeletons probably evolved more than once within the early Gymnolaemata. Bryozoans' relationships with other phyla are uncertain and controversial. Traditional phylogeny, based on anatomy and on the development of the adult forms from embryos , has produced no enduring consensus about the position of ectoprocts. Attempts to reconstruct the family tree of animals have largely ignored ectoprocts and other "minor phyla", which have received little scientific study because they are generally tiny, have relatively simple body plans, and have little impact on human economies – despite
4608-545: Is one of the primary branches of biology . The term is derived from Ancient Greek ζῷον , zōion ('animal'), and λόγος , logos ('knowledge', 'study'). Although humans have always been interested in the natural history of the animals they saw around them, and used this knowledge to domesticate certain species, the formal study of zoology can be said to have originated with Aristotle . He viewed animals as living organisms, studied their structure and development, and considered their adaptations to their surroundings and
4736-415: Is partly based on paleontology , which uses the fossil record to answer questions about the mode and tempo of evolution, and partly on the developments in areas such as population genetics and evolutionary theory. Following the development of DNA fingerprinting techniques in the late 20th century, the application of these techniques in zoology has increased the understanding of animal populations. In
4864-406: Is quantitative, and recently a significant amount of work has been done using computer science techniques such as bioinformatics and computational biology . Molecular genetics , the study of gene structure and function, has been among the most prominent sub-fields of molecular biology since the early 2000s. Other branches of biology are informed by molecular biology, by either directly studying
4992-698: Is reflected in zoology by the presence of animals in Egyptian hieroglyphics. Although the concept of zoology as a single coherent field arose much later, the zoological sciences emerged from natural history reaching back to the biological works of Aristotle and Galen in the ancient Greco-Roman world . In the fourth century BC, Aristotle looked at animals as living organisms, studying their structure, development and vital phenomena. He divided them into two groups: animals with blood, equivalent to our concept of vertebrates , and animals without blood, invertebrates . He spent two years on Lesbos , observing and describing
5120-559: Is the genus, and sapiens the specific epithet, both of them combined make up the species name. When writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the specific epithet in lowercase. Additionally, the entire term may be italicized or underlined. The dominant classification system is called the Linnaean taxonomy . It includes ranks and binomial nomenclature . The classification, taxonomy , and nomenclature of zoological organisms
5248-423: Is the most diverse order of bryozoan, possibly because its members have the widest range of specialist zooids. They have mineralized exoskeletons and form single-layered sheets which encrust over surfaces, and some colonies can creep very slowly by using spiny defensive zooids as legs. Each zooid consists of a "cystid", which provides the body wall and produces the exoskeleton , and a " polypide ", which holds
Tentacle - Misplaced Pages Continue
5376-614: Is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. Evolutionary research is concerned with the origin and descent of species , as well as their change over time, and includes scientists from many taxonomically oriented disciplines. For example, it generally involves scientists who have special training in particular organisms such as mammalogy , ornithology , herpetology , or entomology , but use those organisms as systems to answer general questions about evolution. Evolutionary biology
5504-559: Is uncommon in the fossil record, and relatively little study has been devoted to reassembling fragmented zoaria. The largest known fossil colonies are branching trepostome bryozoans from Ordovician rocks in the United States, reaching 66 centimeters in height. The oldest species with a mineralized skeleton occurs in the Lower Ordovician . It is likely that the first bryozoans appeared much earlier and were entirely soft-bodied, and
5632-670: The Cnidaria tentilla usually bear cnidocytes , whereas in the Ctenophora they usually have collocytes . Siphonophores are an example of Cnidaria that use tentilla. Zoology Zoology ( UK : / z u ˈ ɒ l ə dʒ i / zoo- OL -ə-jee , US : / z oʊ ˈ ɒ l ə dʒ i / zoh- OL -ə-jee ) is the scientific study of animals . Its studies include the structure , embryology , classification , habits , and distribution of all animals, both living and extinct , and how they interact with their ecosystems . Zoology
5760-543: The Mesozoic are fairly equally divided by erect and encrusting forms, and more recent ones are predominantly encrusting. Fossils of the soft, freshwater phylactolaemates are very rare, appear in and after the Late Permian (which began about 260 million years ago ) and consist entirely of their durable statoblasts. There are no known fossils of freshwater members of other classes. Scientists are divided about whether
5888-545: The anatomy of different groups. It is closely related to evolutionary biology and phylogeny (the evolution of species). Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology , but some principles of physiology are universal, no matter what particular organism
6016-508: The anus , which is located on the invert, outside and usually below the lophophore. A network of strands of mesothelium called "funiculi" ("little ropes") connects the mesothelium covering the gut with that lining the body wall. The wall of each strand is made of mesothelium, and surrounds a space filled with fluid, thought to be blood. A colony's zooids are connected, enabling autozooids to share food with each other and with any non-feeding heterozooids. The method of connection varies between
6144-413: The appendages of others. In some species the snapping zooids are mounted on a peduncle (stalk), their bird-like appearance responsible for the term – Charles Darwin described these as like "the head and beak of a vulture in miniature, seated on a neck and capable of movement". Stalked avicularia are placed upside-down on their stalks. The "lower jaws" are modified versions of the opercula that protect
6272-414: The genus Thalamoporella , structures that resemble an open head of lettuce. The most common marine form, however, is encrusting, in which a one-layer sheet of zooids spreads over a hard surface or over seaweed. Some encrusting colonies may grow to over 50 cm (1 ft 8 in) and contain about 2,000,000 zooids. These species generally have exoskeletons reinforced with calcium carbonate , and
6400-550: The proximate causes of the behavior, the developmental history of the organism, the survival value and phylogeny of the behavior? Another area of study is animal cognition , which uses laboratory experiments and carefully controlled field studies to investigate an animal's intelligence and learning. Biogeography studies the spatial distribution of organisms on the Earth , focusing on topics like dispersal and migration , plate tectonics , climate change , and cladistics . It
6528-515: The pulmonate land snails , which usually have two sets of tentacles on the head: when extended the upper pair have eyes at their tips; the lower pair are chemoreceptors . Both pairs are fully retractable muscular hydrostats , but they are not used for manipulation or prey capture. Molluscs have one pair of tentacles close to their mouths that hold close to their captured prey before they can consume it. Some marine snails such as abalone and top snails, Trochidae , have numerous small tentacles around
SECTION 50
#17328511886816656-482: The smell or taste of particular foods or threats. Examples of such tentacles are the eyestalks of various kinds of snails . Some kinds of tentacles have both sensory and manipulatory functions. A tentacle is similar to a cirrus , but a cirrus is an organ that usually lacks the tentacle's strength, size, flexibility, or sensitivity. A nautilus has cirri, but a squid has tentacles. Many molluscs have tentacles of one form or another. The most familiar are those of
6784-399: The taxonomist . Originally it was thought that species were immutable, but with the arrival of Darwin's theory of evolution, the field of cladistics came into being, studying the relationships between the different groups or clades . Systematics is the study of the diversification of living forms, the evolutionary history of a group is known as its phylogeny , and the relationship between
6912-603: The "Ectoprocta" and Entoprocta as close relatives and group them under "Bryozoa". The ambiguity about the scope of the name "Bryozoa" led to proposals in the 1960s and 1970s that it should be avoided and the unambiguous term "Ectoprocta" should be used. However, the change would have made it harder to find older works in which the phylum was called "Bryozoa", and the desire to avoid ambiguity, if applied consistently to all classifications, would have necessitated renaming of several other phyla and many lower-level groups. In practice, zoological naming of split or merged groups of animals
7040-419: The "crown" is a full circle. Among the freshwater bryozoans ( Phylactolaemata ) the crown appears U-shaped, but this impression is created by a deep dent in the rim of the crown, which has no gap in the fringe of tentacles. The sides of the tentacles bear fine hairs called cilia , whose beating drives a water current from the tips of the tentacles to their bases, where it exits. Food particles that collide with
7168-542: The 16th century. During the Renaissance and early modern period, zoological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Andreas Vesalius and William Harvey , who used experimentation and careful observation in physiology , and naturalists such as Carl Linnaeus , Jean-Baptiste Lamarck , and Buffon who began to classify
7296-470: The 1980s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology . Related fields often considered part of evolutionary biology are phylogenetics , systematics , and taxonomy . Ethology is the scientific and objective study of animal behavior under natural conditions, as opposed to behaviorism , which focuses on behavioral response studies in
7424-484: The Bryozoa (Ectoprocta) are a monophyletic group (whether they include all and only a single ancestor species and all its descendants), about what are the phylum's closest relatives in the family tree of animals, and even about whether they should be regarded as members of the protostomes or deuterostomes , the two major groups that account for all moderately complex animals. Molecular phylogeny, which attempts to work out
7552-529: The Cyclostome Bryozoan family Oncousoeciidae." Modern research and experiments have been done using low-vacuum scanning electron microscopy of uncoated type material to critically examine and perhaps revise the taxonomy of three genera belonging to this family, including Oncousoecia , Microeciella , and Eurystrotos . This method permits data to be obtained that would be difficult to recognize with an optical microscope. The valid type species of Oncousoecia
7680-577: The Early Ordovician period, making it the last major phylum to appear in the fossil record. This has led researchers to suspect that bryozoans arose earlier but were initially unmineralized, and may have differed significantly from fossilized and modern forms. In 2021, some research suggested Protomelission , a genus known from the Cambrian period , could be an example of an early bryozoan, but later research suggested that this taxon may instead represent
7808-506: The Entoprocta are not monophyletic, as the Phoronida are a sub-group of ectoprocts but the standard definition of Entoprocta excludes the Phoronida. In 2009 another molecular phylogeny study, using a combination of genes from mitochondria and the cell nucleus , concluded that Bryozoa is a monophyletic phylum, in other words includes all the descendants of a common ancestor that is itself
SECTION 60
#17328511886817936-643: The Ordovician fossils record the appearance of mineralized skeletons in this phylum. By the Arenigian stage of the Early Ordovician period , about 480 million years ago , all the modern orders of stenolaemates were present, and the ctenostome order of gymnolaemates had appeared by the Middle Ordovician, about 465 million years ago . The Early Ordovician fossils may also represent forms that had already become significantly different from
8064-656: The Ordovician period. Bryozoans take responsibility for many of the colony forms, which have evolved in different taxonomic groups and vary in sediment producing ability. The nine basic bryozoan colony-forms include: encrusting, dome-shaped, palmate, foliose, fenestrate, robust branching, delicate branching, articulated and free-living. Most of these sediments come from two distinct groups of colonies: domal, delicate branching, robust branching and palmate; and fenestrate. Fenestrate colonies generate rough particles both as sediment and components of stromatoporoids coral reefs. The delicate colonies however, create both coarse sediment and form
8192-583: The adult cestode to attach to the intestine of the shark or ray that they parasitize. The same tentacles are also present in the larvae. The legless amphibians called caecilians have two short tentacles, one on each side of the head, between their eyes and nostrils. The current opinion is that these tentacles supplement the normal sense of smell, possibly for navigation and to locate prey underground. The star-nosed mole , Condylura cristata , of North America , has 22 short but conspicuous tentacles around its nose. They are mobile and extremely sensitive, helping
8320-488: The animal to find its way about the burrow and detect prey. They are about 1–4 mm long and hold about 25,000 touch receptors called Eimer's organs , perhaps giving this mole the most delicate sense of touch among mammals. The word tentillum ( pl. : tentilla ) literally means "little tentacle". However, irrespective of size, it usually refers to a side branch of a larger tentacle. In some cases, such tentilla are specialised for particular functions; for example, in
8448-418: The animals anchor themselves to sand or gravel and pull themselves through the sediments. Some authorities use the term avicularia (plural of avicularium ) to refer to any type of zooid in which the lophophore is replaced by an extension that serves some protective function, while others restrict the term to those that defend the colony by snapping at invaders and small predators, killing some and biting
8576-449: The animals and plants, considering the adaptations of different organisms and the function of their parts. Four hundred years later, Roman physician Galen dissected animals to study their anatomy and the function of the different parts, because the dissection of human cadavers was prohibited at the time. This resulted in some of his conclusions being false, but for many centuries it was considered heretical to challenge any of his views, so
8704-435: The anus, ectoprocts have hollow tentacles and a coelom , while entoprocts have solid tentacles and no coelom. Hence the two groups are now widely regarded as separate phyla, and the name "Bryozoa" is now synonymous with "Ectoprocta". This has remained the majority view ever since, although most publications have preferred the name "Bryozoa" rather than "Ectoprocta". Nevertheless, some notable scientists have continued to regard
8832-459: The base of the "crown" and they have no coelom . All bryozoans are colonial except for one genus , Monobryozoon . Individual members of a bryozoan colony are about 0.5 mm ( 1 ⁄ 64 in) long and are known as zooids , since they are not fully independent animals. All colonies contain feeding zooids, known as autozooids. Those of some groups also contain non-feeding heterozooids, also known as polymorphic zooids, which serve
8960-402: The body and pushes the invert and lophophore out. In some species the retracted invert and lophophore are protected by an operculum ("lid"), which is closed by muscles and opened by fluid pressure. In one class , a hollow lobe called the "epistome" overhangs the mouth. The gut is U-shaped, running from the mouth, in the center of the lophophore, down into the animal's interior and then back to
9088-582: The body is below with the tentacles pointed upwards. The tentacles of the lion's mane jellyfish may be up to 37 m (121 ft) long. They are hollow and are arranged in 8 groups of between 70 and 150. The longer tentacles are equipped with cnidocytes whose venom paralyses and kills prey. The smaller tentacles guide food into the mouth. Many species of the jellyfish-like ctenophores have two tentacles, while some have none. Their tentacles have adhesive structures called colloblasts or lasso cells . The colloblasts burst open when prey comes in contact with
9216-427: The cells have nuclei or not, as well as differences in the chemical composition of the cell exteriors. Further, each kingdom is broken down recursively until each species is separately classified. The order is: Domain ; kingdom ; phylum ; class ; order ; family ; genus ; species . The scientific name of an organism is generated from its genus and species. For example, humans are listed as Homo sapiens . Homo
9344-434: The clades can be shown diagrammatically in a cladogram . Although someone who made a scientific study of animals would historically have described themselves as a zoologist, the term has come to refer to those who deal with individual animals, with others describing themselves more specifically as physiologists, ethologists, evolutionary biologists, ecologists, pharmacologists, endocrinologists or parasitologists. Although
9472-428: The class Phylactolaemata is most closely related to Stenolaemata and Ctenostomatida , the classes that appear earliest in the fossil record. However, in 2005 a molecular phylogeny study that focused on phylactolaemates concluded that these are more closely related to the phylum Phoronida , and especially to the only phoronid species that is colonial, than they are to the other ectoproct classes. That implies that
9600-689: The colony. Because kenozooids' function is generally structural, they are called "structural polymorphs." Some heterozooids found in extinct trepostome bryozoans, called mesozooids, are thought to have functioned to space the feeding autozooids an appropriate distance apart. In thin sections of trepostome fossils, mesozooids can be seen in between the tubes that held autozooids; they are smaller tubes that are divided along their length by diaphragms, making them look like rows of box-like chambers sandwiched between autozooidal tubes. Gonozooids act as brood chambers for fertilized eggs. Almost all modern cyclostome bryozoans have them, but they can be hard to locate on
9728-399: The colossal squid wield two long rows of swiveling, tri-pointed hooks. Cnidarians , such as jellyfish , sea anemones , Hydra and coral have numerous hair-like tentacles. Cnidarians have huge numbers of cnidocytes on their tentacles. In medusoid form , the body floats on water so that the tentacles hang down in a ring around the mouth. In polyp form, such as sea anemone and coral,
9856-402: The common methods is through ovicells, capsules attached to autozooids. The autozooids possessing ovicells are normally still able to feed, however, so these are not considered heterozooids. "Female" polymorphs are more common than "male" polymorphs, but specialized zooids that produce sperm are also known. These are called androzooids, and some are found in colonies of Odontoporella bishopi ,
9984-463: The cores of deep-water, subphotic biogenic mounds. Nearly all post- bryozoan sediments are made up of growth forms, with the addition to free-living colonies which include significant numbers of various colonies. "In contrast to the Palaeozoic, post-Palaeozoic bryozoans generated sediment varying more widely with the size of their grains; they grow as they moved from mud, to sand, to gravel." The phylum
10112-485: The crown group Bryozoa were colonial, but as an adaptation to a mesopsammal (interstitial spaces in marine sand) life or to deep-sea habitats, secondarily solitary forms have since evolved. Solitary species has been described in four genera ; Aethozooides , Aethozoon , Franzenella and Monobryozoon ). The latter having a statocyst-like organ with a supposed excretory function. The terms Polyzoa and Bryozoa were introduced in 1830 and 1831, respectively. Soon after it
10240-514: The determination of the double helical structure of the DNA molecule by Francis Crick and James Watson in 1953, the realm of molecular biology opened up, leading to advances in cell biology , developmental biology and molecular genetics . The study of systematics was transformed as DNA sequencing elucidated the degrees of affinity between different organisms. Zoology is the branch of science dealing with animals . A species can be defined as
10368-404: The different classes of bryozoans, ranging from quite large gaps in the body walls to small pores through which nutrients are passed by funiculi. There is a nerve ring round the pharynx (throat) and a ganglion that serves as a brain to one side of this. Nerves run from the ring and ganglion to the tentacles and to the rest of the body. Bryozoans have no specialized sense organs, but cilia on
10496-643: The discovery of the structure of DNA by Francis Crick and James Watson in 1953, the realm of molecular biology opened up, leading to advances in cell biology , developmental biology and molecular genetics . The history of zoology traces the study of the animal kingdom from ancient to modern times. Prehistoric people needed to study the animals and plants in their environment to exploit them and survive. Cave paintings, engravings and sculptures in France dating back 15,000 years show bison, horses, and deer in carefully rendered detail. Similar images from other parts of
10624-456: The diversity of life and the fossil record , as well as studying the development and behavior of organisms. Antonie van Leeuwenhoek did pioneering work in microscopy and revealed the previously unknown world of microorganisms , laying the groundwork for cell theory . van Leeuwenhoek's observations were endorsed by Robert Hooke ; all living organisms were composed of one or more cells and could not generate spontaneously. Cell theory provided
10752-490: The edge of the mantle . These are known as pallial tentacles . Among cephalopods , squid have spectacular tentacles. They take the form of highly mobile muscular hydrostats with various appendages such as suction disks and sometimes thorny hooks. Up to the early twentieth century "tentacles" were interchangeably called "arms". These tentacles are made of stalks of axial nerve cords that are covered by circular transverse muscle tissue that contract in response to stimuli. There
10880-422: The evolutionary family tree of organisms by comparing their biochemistry and especially their genes , has done much to clarify the relationships between the better-known invertebrate phyla. However, the shortage of genetic data about "minor phyla" such as bryozoans and entoprocts has left their relationships to other groups unclear. The traditional view is that the Bryozoa are a monophyletic group, in which
11008-444: The fact that the "minor phyla" include most of the variety in the evolutionary history of animals. In the opinion of Ruth Dewel, Judith Winston, and Frank McKinney, "Our standard interpretation of bryozoan morphology and embryology is a construct resulting from over 100 years of attempts to synthesize a single framework for all invertebrates," and takes little account of some peculiar features of ectoprocts. In ectoprocts, all of
11136-449: The feeding apparatus or other specialized organs that take the place of the feeding apparatus. The most common type of zooid is the feeding autozooid, in which the polypide bears a "crown" of hollow tentacles called a lophophore , which captures food particles from the water. In all colonies a large percentage of zooids are autozooids, and some consist entirely of autozooids, some of which also engage in reproduction. The basic shape of
11264-444: The fluid pressure by pulling on a flexible membrane. The actions of these snapping zooids are controlled by small, highly modified polypides that are located inside the "mouth" and bear tufts of short sensory cilia . These zooids appear in various positions: some take the place of autozooids, some fit into small gaps between autozooids, and small avicularia may occur on the surfaces of other zooids. In vibracula, regarded by some as
11392-404: The forms of macroscopic structures such as organs and organ systems. It focuses on how organs and organ systems work together in the bodies of humans and other animals, in addition to how they work independently. Anatomy and cell biology are two studies that are closely related, and can be categorized under "structural" studies. Comparative anatomy is the study of similarities and differences in
11520-431: The foundations for biogeography , ecology and ethology . Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species . These developments, as well as the results from embryology and paleontology , were synthesized in the 1859 publication of Charles Darwin 's theory of evolution by natural selection ; in this Darwin placed the theory of organic evolution on
11648-502: The function of their parts. Modern zoology has its origins during the Renaissance and early modern period, with Carl Linnaeus , Antonie van Leeuwenhoek , Robert Hooke , Charles Darwin , Gregor Mendel and many others. The study of animals has largely moved on to deal with form and function, adaptations, relationships between groups, behaviour and ecology. Zoology has increasingly been subdivided into disciplines such as classification , physiology , biochemistry and evolution . With
11776-437: The greatest numbers of species, possibly because of their wide range of specialist zooids. Under the Linnaean system of classification , which is still used as a convenient way to label groups of organisms, living members of the phylum Bryozoa are divided into: Fossils of about 15,000 bryozoan species have been found. Bryozoans are among the three dominant groups of Paleozoic fossils. Bryozoans with calcitic skeletons were
11904-476: The interactions of molecules in their own right such as in cell biology and developmental biology , or indirectly, where molecular techniques are used to infer historical attributes of populations or species , as in fields in evolutionary biology such as population genetics and phylogenetics . There is also a long tradition of studying biomolecules "from the ground up", or molecularly, in biophysics . Animals generally reproduce by sexual reproduction ,
12032-405: The interior, and no polypide. The functions of these zooids include forming the stems of branching structures, acting as spacers that enable colonies to grow quickly in a new direction, strengthening the colony's branches, and elevating the colony slightly above its substrate for competitive advantages against other organisms. Some kenozooids are hypothesized to be capable of storing nutrients for
12160-404: The largest group of organisms in which any two individuals of the appropriate sex can produce fertile offspring; about 1.5 million species of animal have been described and it has been estimated that as many as 8 million animal species may exist. An early necessity was to identify the organisms and group them according to their characteristics, differences and relationships, and this is the field of
12288-400: The larva's internal organs are destroyed during the metamorphosis to the adult form and the adult's organs are built from the larva's epidermis and mesoderm , while in other bilaterians some organs including the gut are built from endoderm . In most bilaterian embryos the blastopore, a dent in the outer wall, deepens to become the larva's gut, but in ectoprocts the blastopore disappears and
12416-406: The limb featuring peduncles), arms do fall within the general definition of "tentacle" as "a flexible, mobile, and elongated organ" and "tentacle" could be used as an umbrella term . The tentacles of the giant squid and colossal squid have powerful suckers and pointed teeth at the ends. The teeth of the giant squid resemble bottle caps and function like tiny hole saws , while the tentacles of
12544-422: The mesothelium is split into two separate layers, the inner one forming a membranous sac that floats freely and contains the coelom, and the outer one attached to the body wall and enclosing the membranous sac in a pseudocoelom . The other main part of the bryozoan body, known as the polypide and situated almost entirely within the cystid, contains the nervous system, digestive system, some specialized muscles and
12672-554: The most abundant and diverse bryozoans from the Cretaceous to the present. Evidence compiled from the last 100 million years show that cheilostomatids consistently grew over cyclostomatids in territorial struggles, which may help to explain how cheilostomatids replaced cyclostomatids as the dominant marine bryozoans. Marine fossils from the Paleozoic era, which ended 251 million years ago , are mainly of erect forms, those from
12800-466: The openings through which the lophophores protrude are on the top or outer surface. The moss-like appearance of encrusting colonies is responsible for the phylum's name ( Ancient Greek words βρύον brúon meaning 'moss' and ζῷον zôion meaning 'animal'). Large colonies of encrusting species often have " chimneys ", gaps in the canopy of lophophores, through which they swiftly expel water that has been sieved, and thus avoid re-filtering water that
12928-460: The opponent. Some species consistently prevail against certain others, but most turf wars are indecisive and the combatants soon turn to growing in uncontested areas. Bryozoans competing for territory do not use the sophisticated techniques employed by sponges or corals , possibly because the shortness of bryozoan lifespans makes heavy investment in turf wars unprofitable. Bryozoans have contributed to carbonate sedimentation in marine life since
13056-475: The organs. Zooids have no special excretory organs, and autozooids' polypides are scrapped when they become overloaded with waste products; usually the body wall then grows a replacement polypide. Their gut is U-shaped, with the mouth inside the crown of tentacles and the anus outside it. Zooids of all the freshwater species are simultaneous hermaphrodites . Although those of many marine species function first as males and then as females, their colonies always contain
13184-543: The original members of the phylum. Ctenostomes with phosphatized soft tissue are known from the Devonian. Other types of filter feeders appeared around the same time, which suggests that some change made the environment more favorable for this lifestyle. Fossils of cheilostomates , an order of gymnolaemates with mineralized skeletons, first appear in the Mid Jurassic , about 172 million years ago , and these have been
13312-536: The past. A new genus has also been recently discovered called Junerossia in the family Stomachetosellidae, along with 10 relatively new species of bryozoa such as Alderina flaventa , Corbulella extenuata , Puellina septemcryptica , Junerossia copiosa , Calyptotheca kapaaensis , Bryopesanser serratus , Cribellopora souleorum , Metacleidochasma verrucosa , Disporella compta , and Favosipora adunca . Counts of formally described species range between 4,000 and 4,500. The Gymnolaemata and especially Cheilostomata have
13440-562: The pattern of budding by which they grow, the variety of zooids present and the type and amount of skeletal material they secrete . Some marine species are bush-like or fan-like, supported by "trunks" and "branches" formed by kenozooids, with feeding autozooids growing from these. Colonies of these types are generally unmineralized but may have exoskeletons made of chitin . Others look like small corals , producing heavy lime skeletons. Many species form colonies which consist of sheets of autozooids. These sheets may form leaves, tufts or, in
13568-482: The phylum Bryozoa, because both groups were sessile animals that filter-fed by means of a crown of tentacles that bore cilia . From 1869 onwards increasing awareness of differences, including the position of the entoproct anus inside the feeding structure and the difference in the early pattern of division of cells in their embryos , caused scientists to regard the two groups as separate phyla, and "Bryozoa" became just an alternative name for ectoprocts, in which
13696-517: The processes by which animals and plants reproduce and grow. The discipline includes the study of embryonic development , cellular differentiation , regeneration , asexual and sexual reproduction , metamorphosis , and the growth and differentiation of stem cells in the adult organism. Development of both animals and plants is further considered in the articles on evolution , population genetics , heredity , genetic variability , Mendelian inheritance , and reproduction . Evolutionary biology
13824-493: The questions regarding the mechanisms of genetic inheritance and the structure of the gene . In 1953, James Watson and Francis Crick described the structure of DNA and the interactions within the molecule, and this publication jump-started research into molecular biology and increased interest in the subject. While researchers practice techniques specific to molecular biology, it is common to combine these with methods from genetics and biochemistry . Much of molecular biology
13952-494: The results of his own investigations. His general approach was surprisingly modern, and he wrote, "For it is [the task] of natural science not simply to accept what we are told but to inquire into the causes of natural things." An early pioneer was Conrad Gessner , whose monumental 4,500-page encyclopedia of animals, Historia animalium , was published in four volumes between 1551 and 1558. In Europe, Galen's work on anatomy remained largely unsurpassed and unchallenged up until
14080-448: The retracted lophophores in autozooids of some species, and are snapped shut "like a mousetrap" by similar muscles, while the beak-shaped upper jaw is the inverted body wall. In other species the avicularia are stationary box-like zooids laid the normal way up, so that the modified operculum snaps down against the body wall. In both types the modified operculum is opened by other muscles that attach to it, or by internal muscles that raise
14208-503: The rise of the germ theory of disease , though the mechanism of inheritance remained a mystery. In the early 20th century, the rediscovery of Mendel's work led to the rapid development of genetics , and by the 1930s the combination of population genetics and natural selection in the modern synthesis created evolutionary biology . Research in cell biology is interconnected to other fields such as genetics, biochemistry , medical microbiology , immunology , and cytochemistry . With
14336-499: The structures and mechanisms specific to those groups. The rest of the animal kingdom is dealt with by invertebrate zoology , a vast and very diverse group of animals that includes sponges , echinoderms , tunicates , worms , molluscs , arthropods and many other phyla , but single-celled organisms or protists are not usually included. Cell biology studies the structural and physiological properties of cells , including their behavior , interactions, and environment . This
14464-529: The study of anatomy stultified. During the post-classical era , Middle Eastern science and medicine was the most advanced in the world, integrating concepts from Ancient Greece, Rome, Mesopotamia and Persia as well as the ancient Indian tradition of Ayurveda , while making numerous advances and innovations. In the 13th century, Albertus Magnus produced commentaries and paraphrases of all Aristotle's works; his books on topics like botany , zoology, and minerals included information from ancient sources, but also
14592-565: The study of animal life is ancient, its scientific incarnation is relatively modern. This mirrors the transition from natural history to biology at the start of the 19th century. Since Hunter and Cuvier , comparative anatomical study has been associated with morphography , shaping the modern areas of zoological investigation: anatomy , physiology , histology , embryology , teratology and ethology . Modern zoology first arose in German and British universities. In Britain, Thomas Henry Huxley
14720-485: The surface of colonies, which probably are for defense. Some species have miniature nanozooids with small single-tentacled polypides, and these may grow on other zooids or within the body walls of autozooids that have degenerated. Although zooids are microscopic, colonies range in size from 1 cm ( 1 ⁄ 2 in) to over 1 m (3 ft 3 in). However, the majority are under 10 cm (4 in) across. The shapes of colonies vary widely, depend on
14848-440: The surface. A few species can creep at about 2 cm ( 3 ⁄ 4 in) per day. Each colony grows by asexual budding from a single zooid known as the ancestrula, which is round rather than shaped like a normal zooid. This occurs at the tips of "trunks" or "branches" in forms that have this structure. Encrusting colonies grow round their edges. In species with calcareous exoskeletons, these do not mineralize until
14976-449: The tentacle, releasing sticky threads that secure the food. Bryozoa (moss animals) are tiny creatures with tentacles around their mouths. The tentacles are almost cylindrical and have bands of cilia which create a water current towards the mouth. The animal extracts edible material from the flow of water. Trypanorhynch cestodes are parasitic in fish. Their scolex shows four tentacles which are covered by spines. These tentacles help
15104-487: The tentacles act as sensors. Members of the genus Bugula grow towards the sun , and therefore must be able to detect light. In colonies of some species, signals are transmitted between zooids through nerves that pass through pores in the body walls, and coordinate activities such as feeding and the retraction of lophophores. The solitary individuals of Monobryozoon are autozooids with pear-shaped bodies. The wider ends have up to 15 short, muscular projections by which
15232-437: The tentacles are trapped by mucus , and further cilia on the inner surfaces of the tentacles move the particles towards the mouth in the center. The method used by ectoprocts is called "upstream collecting", as food particles are captured before they pass through the field of cilia that creates the feeding current. This method is also used by phoronids , brachiopods and pterobranchs . The lophophore and mouth are mounted on
15360-433: The time. Darwin gave a new direction to morphology and physiology , by uniting them in a common biological theory: the theory of organic evolution. The result was a reconstruction of the classification of animals upon a genealogical basis, fresh investigation of the development of animals, and early attempts to determine their genetic relationships. The end of the 19th century saw the fall of spontaneous generation and
15488-406: The tips of the tentacles may check for signs of danger before the invert and lophophore are fully extended. Extension is driven by an increase in internal fluid pressure, which species with flexible exoskeletons produce by contracting circular muscles that lie just inside the body wall, while species with a membranous sac use circular muscles to squeeze this. Some species with rigid exoskeletons have
15616-551: The water by means of a lophophore , a "crown" of hollow tentacles. Bryozoans form colonies consisting of clones called zooids that are typically about 0.5 mm ( 1 ⁄ 64 in) long. Phoronids resemble bryozoan zooids but are 2 to 20 cm (1 to 8 in) long and, although they often grow in clumps, do not form colonies consisting of clones. Brachiopods, generally thought to be closely related to bryozoans and phoronids, are distinguished by having shells rather like those of bivalves . All three of these phyla have
15744-489: The world illustrated mostly the animals hunted for food and the savage animals. The Neolithic Revolution , which is characterized by the domestication of animals , continued throughout Antiquity. Ancient knowledge of wildlife is illustrated by the realistic depictions of wild and domestic animals in the Near East, Mesopotamia, and Egypt, including husbandry practices and techniques, hunting and fishing. The invention of writing
15872-509: The zooids are fully grown. Colony lifespans range from one to about 12 years, and the short-lived species pass through several generations in one season. Species that produce defensive zooids do so only when threats have already appeared, and may do so within 48 hours. The theory of "induced defenses" suggests that production of defenses is expensive and that colonies which defend themselves too early or too heavily will have reduced growth rates and lifespans. This "last minute" approach to defense
16000-502: Was a prominent figure. His ideas were centered on the morphology of animals. Many consider him the greatest comparative anatomist of the latter half of the 19th century. Similar to Hunter , his courses were composed of lectures and laboratory practical classes in contrast to the previous format of lectures only. Scientific classification in zoology , is a method by which zoologists group and categorize organisms by biological type , such as genus or species . Biological classification
16128-576: Was found to be Oncousoecia lobulata . This interpretation stabilizes Oncousoecia by establishing a type species that corresponds to the general usage of the genus. Fellow Oncousoeciid Eurystrotos is now believed to be not conspecific with O. lobulata , as previously suggested, but shows enough similarities to be considered a junior synonym of Oncousoecia . Microeciella suborbicularus has also been recently distinguished from O. lobulata and O. dilatans , using this modern method of low vacuum scanning, with which it has been inaccurately synonymized with in
16256-438: Was named, another group of animals was discovered whose filtering mechanism looked similar, so it was included in Bryozoa until 1869, when the two groups were noted to be very different internally. The new group was given the name " Entoprocta ", while the original Bryozoa were called "Ectoprocta". Disagreements about terminology persisted well into the 20th century, but "Bryozoa" is now the generally accepted term. Colonies take
16384-455: Was originally called "Polyzoa", but this name was eventually replaced by Ehrenberg's term "Bryozoa". The name "Bryozoa" was originally applied only to the animals also known as Ectoprocta ( lit. ' outside-anus ' ), in which the anus lies outside the "crown" of tentacles. After the discovery of the Entoprocta ( lit. ' inside-anus ' ), in which the anus lies within
#680319