Nepomorpha is an

infraorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

insect Insects (from Latin ') are pancrustacean 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 ...

s in the "true bug"

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

( Hemiptera). They belong to the "typical" bugs of the

suborder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

Heteroptera. Due to their aquatic habits, these

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s are known as true water bugs. They occur all over the world outside the

polar region The polar regions, also called the frigid zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North and South Poles), lying within the polar circles. These high latitudes are dominated by flo ...

s, with about 2,000

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

altogether. The Nepomorpha can be distinguished from related Heteroptera by their missing or vestigial

ocelli A simple eye (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-le ...

. Also, as referred to by the obsolete name Cryptocerata ("the hidden-horned ones"), their antennae are reduced, with weak muscles, and usually carried tucked against the head. Most of the

within this infraorder live in

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does in ...

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s. The exceptions are members of the superfamily Ochteroidea, which are found along the water's edge. Many of these insects are

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

s of

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s and in some cases – like the large water scorpions (Nepidae) and giant water bugs (Belostomatidae) – even small

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...

and amphibians. Others are

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...

s or feed on

plant Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...

s. Their

mouthparts Mouthparts may refer to: * The parts of a mouth ** Arthropod mouthparts *** Insect mouthparts {{disambig ...

form a rostrum as in all Heteroptera and most Hemiptera. With this, they pierce their food source to suck out fluids; some, like the

Corixidae Corixidae is a family of aquatic insects in the order Hemiptera. They are found worldwide in virtually any freshwater habitat and a few species live in saline water. There are about 500 known species worldwide, in 55 genera, including the genus ...

, are also able to chew their food to some extent, sucking up the resulting pulp. The rostrum can also be used to sting in defence; some, like the common backswimmer ('' Notonecta glauca'') of the Notonectidae can easily pierce the skin of humans and deliver a wound often more painful than a

bee Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyly, monophyletic lineage within the ...

's sting.

Systematics

The Nepomorpha probably originated around the start of the

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a ...

, some . As evidenced by

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s such as the rather advanced Triassocoridae or the primitive water boatman '' Lufengnacta'', the radiation establishing today's superfamilies seems to have been largely complete by the end of the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

. There are a large number of fossil genera, but except those placed in Triassocoridae they can at least tentatively be assigned to the extant superfamilies. Though the

systematics Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic t ...

and

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...

of the higher

taxa In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

of Nepomorpha were long controversial,

cladistic analysis Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived ch ...

mitochondrial A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

16S and

nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space * Nuclear ...

28S rDNA

sequence In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is called ...

data and morphology has more recently resolved to near-perfection. The long-accepted superfamilies are all

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic ...

, with the exception of the Naucoroidea, which is now

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

with the Aphelocheiridae and Potamocoridae being split off in a new superfamily Aphelocheiroidea. The Cibariopectinata, a proposed clade established on the presence of cibariopectine structures in the food-sucking pump of some of the most advanced true water bugs ( Tripartita), might indeed be monophyletic. Alternatively it might be synonymous with the Tripartita, the Ochteroidea having lost the cibariopectines again due to the different requirements of their (for Nepomorpha) unusual lifestyle. About seven superfamilies, in

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

ary sequence, from the most ancient to the most modern lineage, have been identified in the Infraorder Nepomorpha: * †'' Morrisonnepa'' (''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'':

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone, ...

Tithonian In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by t ...

~ 151 Ma.)

Nepoidea

* Family Belostomatidae – giant water bugs * Family Nepidae – water scorpions

Corixoidea

* Family

– water boatmen

Ochteroidea

; Clade Tripartita * Family Gelastocoridae – toad bugs * Family Ochteridae – velvety shore bugs ;Clade Cibariopectinata (disputed) * Family Triassocoridae (

, tentatively placed here)

Aphelocheiroidea

* Family Aphelocheiridae * Family Potamocoridae

Naucoroidea

* Family

Naucoridae Naucoridae is a small family of insects commonly known as the creeping water bugs and saucer bugs. They are similar in appearance and behavior to Belostomatidae (giant water bugs), but considerably smaller, at long. Naucoridae are found around th ...

– creeping water bugs

Notonectoidea

* Family Notonectidae – backswimmers

Pleoidea Nepomorpha is an infraorder of insects in the "true bug" order ( Hemiptera). They belong to the "typical" bugs of the suborder Heteroptera. Due to their aquatic habits, these animals are known as true water bugs. They occur all over the world ...

Note: sometimes included in Notonectoidea * Family

Helotrephidae Helotrephidae is a family of aquatic bugs found mainly in the tropical regions with many species in the Oriental Realm The Indomalayan realm is one of the eight biogeographic realms. It extends across most of South and Southeast Asia and in ...

* Family

Pleidae Pleidae, the pygmy backswimmers, is a family of aquatic insects in the order Hemiptera (infraorder Nepomorpha, or "true water bugs"). There are 37 species in three genera, distributed across most of the world, except the polar regions and remote ...

– pygmy backswimmers

Systematics

Nepoidea

Corixoidea

Ochteroidea

Aphelocheiroidea

Naucoroidea

Notonectoidea

Pleoidea Nepomorpha is an infraorder of insects in the "true bug" order ( Hemiptera). They belong to the "typical" bugs of the suborder Heteroptera. Due to their aquatic habits, these animals are known as true water bugs. They occur all over the world ...

Footnotes

Further reading