54-552: See text Neritopsina Cox & Knight, 1960 Neritimorpha is a clade of gastropod molluscs that contains around 2,000 extant species of sea snails , limpets , freshwater snails , land snails and slugs . This clade used to be known as the superorder Neritopsina . The clade’s name, Neritimorpha, is from the Ancient Greek νηρίτης (nērī́tēs 'Nerite') and μορφή (morphḗ 'form'). Despite their relatively low diversity, with only around 2,000 species, neritomorphs have achieved
108-531: A warning , when they are poisonous or contain stinging cells , or to camouflage them on the brightly colored hydroids , sponges , and seaweeds on which many of the species are found. Lateral outgrowths on the body of nudibranchs are called cerata . These contain an outpocketing of digestive glands called the diverticula . The sensory organs of gastropods include olfactory organs , eyes, statocysts and mechanoreceptors . Gastropods have no hearing. In terrestrial gastropods (land snails and slugs),
162-479: A few ciliary feeders, in which the radula is reduced or absent. Land-dwelling species can chew up leaves, bark, fruit and decomposing animals while marine species can scrape algae off the rocks on the seafloor. Certain species such as the Archaeogastropda maintain horizontal rows of slender marginal teeth. In some species that have evolved into endoparasites, such as the eulimid Thyonicola doglieli , many of
216-441: A fossil record. Gastropoda (previously known as univalves and sometimes spelled "Gasteropoda") are a major part of the phylum Mollusca, and are the most highly diversified class in the phylum , with 65,000 to 80,000 living snail and slug species . The anatomy , behavior, feeding, and reproductive adaptations of gastropods vary significantly from one clade or group to another, so stating many generalities for all gastropods
270-400: A gastropod is called a protoconch . Most shelled gastropods have a one piece shell (with exceptional bivalved gastropods ), typically coiled or spiraled, at least in the larval stage. This coiled shell usually opens on the right-hand side (as viewed with the shell apex pointing upward). Numerous species have an operculum , which in many species acts as a trapdoor to close the shell. This
324-446: A gastropod is usually adapted to the food that a species eats. The simplest gastropods are the limpets and abalones , herbivores that use their hard radula to rasp at seaweeds on rocks. Many marine gastropods are burrowers, and have a siphon that extends out from the mantle edge. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw water into their mantle cavity and over
378-552: A hundred species, are marine. Insects such as snow scorpionflies flourish in cold habitats including the Arctic and at high altitude. Insects such as desert locusts , ants, beetles, and termites are adapted to some of the hottest and driest environments on earth, such as the Sonoran Desert . Insects form a clade , a natural group with a common ancestor, among the arthropods . A phylogenetic analysis by Kjer et al. (2016) places
432-399: A large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ( / ɡ æ s ˈ t r ɒ p ə d ə / ). This class comprises snails and slugs from saltwater, freshwater, and from the land. There are many thousands of species of sea snails and slugs , as well as freshwater snails , freshwater limpets , land snails and slugs . The class Gastropoda
486-477: A leftover of early gastropod diversification. Neritimorpha is the sister taxon of the Apogastropoda . The clade uniting neritimorphs and apogastropods has been called either Adenogonogastropoda or Angiogastropoda. All modern members of Neritimorpha are classified in the order Cycloneritimorpha . Neritopsoidea was the first of the four modern neritomorph superfamilies to diverge from the others. According to
540-491: A marine environment. Gastropods have a worldwide distribution, from the near Arctic and Antarctic zones to the tropics. They have become adapted to almost every kind of existence on earth, having colonized nearly every available medium. In habitats where not enough calcium carbonate is available to build a really solid shell, such as on some acidic soils on land, various species of slugs occur, and also some snails with thin, translucent shells, mostly or entirely composed of
594-402: A reference to the fact that the animal's "foot" is positioned below its guts. The earlier name "univalve" means one valve (or shell), in contrast to bivalves , such as clams, which have two valves or shells. At all taxonomic levels, gastropods are second only to insects in terms of their diversity . Gastropods have the greatest numbers of named mollusk species. However, estimates of
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#1732858677031648-405: A remarkable diversity of forms, resembling a smaller-scale version of the diversity achieved by Gastropoda as a whole. Terrestrial lifestyles have evolved at least three separate occasions in neritimorphs: the extinct Dawsonellidae and the extant Helicinidae and Hydrocenidae . Neritimorphs also include the shellless, slug -like Titiscania . In all modern neritomorphs except neritopsids,
702-464: Is a diverse and highly successful class of mollusks within the phylum Mollusca. It contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes back to the Late Cambrian . As of 2017 , 721 families of gastropods are known, of which 245 are extinct and appear only in the fossil record, while 476 are currently extant with or without
756-472: Is a part of the behavior of mating gastropods with some pulmonate families of land snails creating and utilizing love darts , the throwing of which have been identified as a form of sexual selection . The main aspects of the life cycle of gastropods include: The diet of gastropods differs according to the group considered. Marine gastropods include some that are herbivores , detritus feeders, predatory carnivores , scavengers , parasites , and also
810-423: Is constrained by the inelastic exoskeleton, so development involves a series of molts . The immature stages often differ from the adults in structure, habit and habitat. Groups that undergo four-stage metamorphosis often have a nearly immobile pupa . Insects that undergo three-stage metamorphosis lack a pupa, developing through a series of increasingly adult-like nymphal stages. The higher level relationship of
864-422: Is difficult. The class Gastropoda has an extraordinary diversification of habitats . Representatives live in gardens, woodland, deserts, and on mountains; in small ditches, great rivers, and lakes; in estuaries , mudflats , the rocky intertidal , the sandy subtidal, the abyssal depths of the oceans, including the hydrothermal vents , and numerous other ecological niches, including parasitic ones. Although
918-433: Is muscular, and the second is mutagenetic . The effects of torsion are primarily physiological. The organism develops by asymmetrical growth, with the majority of growth occurring on the left side. This leads to the loss of right-side anatomy that in most bilaterians is a duplicate of the left side anatomy. The essential feature of this asymmetry is that the anus generally lies to one side of the median plane. The gill-combs ,
972-470: Is not the most important sense, because they are mainly nocturnal animals. The nervous system of gastropods includes the peripheral nervous system and the central nervous system . The central nervous system consists of ganglia connected by nerve cells. It includes paired ganglia: the cerebral ganglia, pedal ganglia, osphradial ganglia, pleural ganglia, parietal ganglia and the visceral ganglia. There are sometimes also buccal ganglia. The radula of
1026-407: Is only partly contained in vessels, and some circulates in an open hemocoel . Insect vision is mainly through their compound eyes , with additional small ocelli . Many insects can hear, using tympanal organs , which may be on the legs or other parts of the body. Their sense of smell is via receptors, usually on the antennae and the mouthparts. Nearly all insects hatch from eggs . Insect growth
1080-623: Is probably not even a mollusk. As such, it's not until the Ordovician that the first crown-group members arise. By the Ordovician period the gastropods were a varied group present in a range of aquatic habitats. Commonly, fossil gastropods from the rocks of the early Palaeozoic era are too poorly preserved for accurate identification. Still, the Silurian genus Poleumita contains fifteen identified species. Fossil gastropods were less common during
1134-460: Is usually made of a horn-like material, but in some molluscs it is calcareous. In the land slugs, the shell is reduced or absent, and the body is streamlined. Some gastropods have adult shells which are bottom heavy due to the presence of a thick, often broad, convex ventral callus deposit on the inner lip and adapical to the aperture which may be important for gravitational stability. Some sea slugs are very brightly colored. This serves either as
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#17328586770311188-830: The Latin word insectum from in , "cut up", as insects appear to be cut into three parts. The Latin word was introduced by Pliny the Elder who calqued the Ancient Greek word ἔντομον éntomon "insect" (as in entomology ) from ἔντομος éntomos "cut in pieces"; this was Aristotle 's term for this class of life in his biology , also in reference to their notched bodies. The English word insect first appears in 1601 in Philemon Holland 's translation of Pliny. In common speech, insects and other terrestrial arthropods are often called bugs . Entomologists to some extent reserve
1242-624: The Palaeozoic era than bivalves . Most of the gastropods of the Palaeozoic era belong to primitive groups, a few of which still survive. By the Carboniferous period many of the shapes seen in living gastropods can be matched in the fossil record, but despite these similarities in appearance the majority of these older forms are not directly related to living forms. It was during the Mesozoic era that
1296-473: The Planorbidae , have hemoglobin as the respiratory protein. In one large group of sea slugs, the gills are arranged as a rosette of feathery plumes on their backs, which gives rise to their other name, nudibranchs . Some nudibranchs have smooth or warty backs with no visible gill mechanism, such that respiration may likely take place directly through the skin. Gastropods have open circulatory system and
1350-474: The continental slope and the continental rise are home to the highest diversity, while the continental shelf and abyssal depths have a low diversity of marine gastropods. Gastropods are found in a wide range of aquatic and terrestrial habitats, from deep ocean trenches to deserts. Some of the more familiar and better-known gastropods are terrestrial gastropods (the land snails and slugs). Some live in fresh water, but most named species of gastropods live in
1404-616: The insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonfly-like insects with wingspans of 55 to 70 cm (22 to 28 in). The most diverse insect groups appear to have coevolved with flowering plants . Adult insects typically move about by walking and flying; some can swim. Insects are the only invertebrates that can achieve sustained powered flight; insect flight evolved just once. Many insects are at least partly aquatic , and have larvae with gills; in some species,
1458-446: The olfactory organs , the foot slime-gland , nephridia , and the auricle of the heart are single or at least are more developed on one side of the body than the other. Furthermore, there is only one genital orifice, which lies on the same side of the body as the anus. Furthermore, the anus becomes redirected to the same space as the head. This is speculated to have some evolutionary function, as prior to torsion, when retracting into
1512-483: The pheromones of female moths over great distances. Other species communicate with sounds: crickets stridulate , or rub their wings together, to attract a mate and repel other males. Lampyrid beetles communicate with light. Humans regard many insects as pests , especially those that damage crops, and attempt to control them using insecticides and other techniques. Others are parasitic , and may act as vectors of diseases . Insect pollinators are essential to
1566-544: The taxonomy of the Gastropoda (Ponder & Lindberg, 1997) Neritopsina is a gastropod superorder in the subclass Orthogastropoda . The superfamily Palaeotrochoidea is contained within Neritopsina but its order placement is undetermined. The taxonomy of the Gastropoda by Bouchet & Rocroi, 2005 categorizes Neritimorpha as a gastropod mollusk clade . It is one of the 6 highest clades in Gastropoda. It contains
1620-618: The Hemiptera (true bugs), Lepidoptera (butterflies and moths), Diptera (true flies), Hymenoptera (wasps, ants, and bees), and Coleoptera (beetles), each with more than 100,000 described species. Insects are distributed over every continent and almost every terrestrial habitat. There are many more species in the tropics , especially in rainforests , than in temperate zones. The world's regions have received widely differing amounts of attention from entomologists. The British Isles have been thoroughly surveyed, so that Gullan and Cranston 2014 state that
1674-476: The adult stage—though in some, the coiling may not be very visible, for example in cowries . In a number of families of species, such as all the various limpets , the shell is coiled only in the larval stage, and is a simple conical structure after that. In the scientific literature, gastropods were described as "gasteropodes" by Georges Cuvier in 1795. The word gastropod comes from Greek γαστήρ ( gastḗr 'stomach') and πούς ( poús 'foot'),
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1728-404: The adults too are aquatic. Some species, such as water striders , can walk on the surface of water. Insects are mostly solitary, but some, such as bees , ants and termites , are social and live in large, well-organized colonies . Others, such as earwigs , provide maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense
1782-411: The ancestors of many of the living gastropods evolved. Insect Insects (from Latin insectum ) are hexapod invertebrates of the class Insecta . They are the largest group within the arthropod phylum . Insects have a chitinous exoskeleton , a three-part body ( head , thorax and abdomen ), three pairs of jointed legs , compound eyes , and a pair of antennae . Insects are
1836-535: The body cavity, and digestive glands opening into the stomach . Courtship is a part of mating behavior in some gastropods, including some of the Helicidae . Again, in some land snails, an unusual feature of the reproductive system of gastropods is the presence and utilization of love darts . In many marine gastropods other than the opisthobranchs , there are separate sexes ( dioecious / gonochoric ); most land gastropods, however, are hermaphrodites . Courtship
1890-521: The clades Cyrtoneritimorpha , Cycloneritimorpha , as well as Paleozoic Neritimorpha of uncertain position. Clades (and uncertain position taxa) in Neritimorpha include: Four extant superfamilies are recognised: Helicinoidea , Hydrocenoidea , Neritoidea and Neritopsoidea . Nerite snails are popular in the aquarium trade. Gastropod Gastropods ( / ˈ ɡ æ s t r ə p ɒ d z / ), commonly known as slugs and snails , belong to
1944-423: The deep-sea floor has been studied biologically. The total number of living species of freshwater snails is about 4,000. Recently extinct species of gastropods (extinct since 1500) number 444, 18 species are now extinct in the wild (but still exist in captivity), and 69 species are "possibly extinct". The number of prehistoric (fossil) species of gastropods is at least 15,000 species. In marine habitats,
1998-425: The earliest representatives of the group appearing in the Late Cambrian ( Chippewaella , Strepsodiscus ), though their only gastropod character is a coiled shell, so they could lie in the stem lineage, if they are gastropods at all. Earliest Cambrian organisms like Helcionella , Barskovia and Scenella are no longer considered gastropods, and the tiny coiled Aldanella of earliest Cambrian time
2052-411: The gill. They use the siphon primarily to "taste" the water to detect prey from a distance. Gastropods with siphons tend to be either predators or scavengers. Almost all marine gastropods breathe with a gill , but many freshwater species, and the majority of terrestrial species, have a pallial lung . The respiratory protein in almost all gastropods is hemocyanin , but one freshwater pulmonate family,
2106-471: The inner walls of the protoconch are resorbed. Unlike most other gastropods, neritomorphs typically have calcified opercula . There is no operculum in the shellless Titiscania , and the Phenacolepadidae have a vestigial, non-calcified operculum that shows no postlarval growth. Neritimorpha has an extremely rich geologic history, going back to early Ordovician . This clade has been considered to be
2160-592: The insects among the Hexapoda , six-legged animals with segmented bodies; their closest relatives are the Diplura (bristletails). Collembola (springtails) [REDACTED] Protura (coneheads) [REDACTED] Diplura (two-pronged bristletails) [REDACTED] Insecta (=Ectognatha) [REDACTED] The internal phylogeny is based on the works of Wipfler et al. 2019 for the Polyneoptera , Johnson et al. 2018 for
2214-446: The most diverse group of animals, with more than a million described species ; they represent more than half of all animal species. The insect nervous system consists of a brain and a ventral nerve cord . Most insects reproduce by laying eggs . Insects breathe air through a system of paired openings along their sides, connected to small tubes that take air directly to the tissues. The blood therefore does not carry oxygen; it
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2268-402: The name "bugs" for a narrow category of " true bugs ", insects of the order Hemiptera , such as cicadas and shield bugs . Other terrestrial arthropods, such as centipedes , millipedes , woodlice , spiders , mites and scorpions , are sometimes confused with insects, since they have a jointed exoskeleton. Adult insects are the only arthropods that ever have wings, with up to two pairs on
2322-572: The name "snail" can be, and often is, applied to all the members of this class, commonly this word means only those species with an external shell big enough that the soft parts can withdraw completely into it. Slugs are gastropods that have no shell or a very small, internal shell; semislugs are gastropods that have a shell that they can partially retreat into but not entirely. The marine shelled species of gastropods include species such as abalone , conches , periwinkles , whelks , and numerous other sea snails that produce seashells that are coiled in
2376-486: The olfactory organs, located on the tips of the four tentacles , are the most important sensory organ. The chemosensory organs of opisthobranch marine gastropods are called rhinophores . The majority of gastropods have simple visual organs, eye spots either at the tip or base of the tentacles. However, "eyes" in gastropods range from simple ocelli that only distinguish light and dark, to more complex pit eyes , and even to lens eyes . In land snails and slugs, vision
2430-502: The origin of Patellogastropoda and Heterobranchia , whereas fewer changes occurred between the ancestors of Vetigastropoda (only tRNAs D, C and N) and Caenogastropoda (a large single inversion , and translocations of the tRNAs D and N). Within Heterobranchia, gene order seems relatively conserved, and gene rearrangements are mostly related with transposition of tRNA genes. The first gastropods were exclusively marine, with
2484-555: The protein conchiolin . Snails such as Sphincterochila boissieri and Xerocrassa seetzeni have adapted to desert conditions. Other snails have adapted to an existence in ditches, near deepwater hydrothermal vents , in oceanic trenches 10,000 meters (6 miles) below the surface, the pounding surf of rocky shores , caves , and many other diverse areas. Gastropods can be accidentally transferred from one habitat to another by other animals, e.g. by birds . Snails are distinguished by an anatomical process known as torsion , where
2538-535: The reproduction of many flowering plants and so to their ecosystems. Many insects are ecologically beneficial as predators of pest insects, while a few provide direct economic benefit. Two species in particular are economically important and were domesticated many centuries ago: silkworms for silk and honey bees for honey . Insects are consumed as food in 80% of the world's nations, by people in roughly 3000 ethnic groups. Human activities are having serious effects on insect biodiversity . The word insect comes from
2592-419: The shell, first the posterior end would get pulled in, and then the anterior. Now, the front can be retracted more easily, perhaps suggesting a defensive purpose. Gastropods typically have a well-defined head with two or four sensory tentacles with eyes, and a ventral foot. The foremost division of the foot is called the propodium. Its function is to push away sediment as the snail crawls. The larval shell of
2646-593: The standard gastropod features are strongly reduced or absent. A few sea slugs are herbivores and some are carnivores. The carnivorous habit is due to specialisation. Many gastropods have distinct dietary preferences and regularly occur in close association with their food species. Some predatory carnivorous gastropods include: cone shells , Testacella , Daudebardia , turrids , ghost slugs and others. Gastropods exhibit an important degree of variation in mitochondrial gene organization when compared to other animals. Main events of gene rearrangement occurred at
2700-527: The thorax. Whether winged or not, adult insects can be distinguished by their three-part body plan, with head, thorax, and abdomen; they have three pairs of legs on the thorax. Estimates of the total number of insect species vary considerably, suggesting that there are perhaps some 5.5 million insect species in existence, of which about one million have been described and named. These constitute around half of all eukaryote species, including animals , plants , and fungi . The most diverse insect orders are
2754-715: The total number of gastropod species vary widely, depending on cited sources. The number of gastropod species can be ascertained from estimates of the number of described species of Mollusca with accepted names: about 85,000 (minimum 50,000, maximum 120,000). But an estimate of the total number of Mollusca, including undescribed species, is about 240,000 species. The estimate of 85,000 mollusks includes 24,000 described species of terrestrial gastropods. Different estimates for aquatic gastropods (based on different sources) give about 30,000 species of marine gastropods, and about 5,000 species of freshwater and brackish gastropods. Many deep-sea species remain to be discovered, as only 0.0001% of
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#17328586770312808-518: The total of around 22,500 species is probably within 5% of the actual number there; they comment that Canada's list of 30,000 described species is surely over half of the actual total. They add that the 3000 species of the American Arctic must be broadly accurate. In contrast, a large majority of the insect species of the tropics and the southern hemisphere are probably undescribed. Some 30–40,000 species inhabit freshwater ; very few insects, perhaps
2862-437: The transport fluid is hemolymph . Hemocyanin is present in the hemolymph as the respiratory pigment. The primary organs of excretion in gastropods are nephridia , which produce either ammonia or uric acid as a waste product. The nephridium also plays an important role in maintaining water balance in freshwater and terrestrial species. Additional organs of excretion, at least in some species, include pericardial glands in
2916-406: The visceral mass of the animal rotates 180° to one side during development, such that the anus is situated more or less above the head. This process is unrelated to the coiling of the shell, which is a separate phenomenon. Torsion is present in all gastropods, but the opisthobranch gastropods are secondarily untorted to various degrees. Torsion occurs in two stages. The first, mechanistic stage
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