Nepomorpha is an infraorder of

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 pa ...

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 ...

(

Hemiptera Hemiptera (; ) is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from to arou ...

). 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 The Heteroptera are a group of about 40,000 species of insects in the order Hemiptera. They are sometimes called "true bugs", though that name more commonly refers to the Hemiptera as a whole. "Typical bugs" might be used as a more unequivocal al ...

. Due to their aquatic habits, these

animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

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 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 the appropriat ...

altogether. The Nepomorpha can be distinguished from related Heteroptera by their missing or vestigial ocelli. Also, as referred to by the obsolete name Cryptocerata ("the hidden-horned ones"), their

antenna Antenna ( antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two collid ...

e 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 incl ...

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 SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

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 t ...

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 chorda ...

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

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

and

amphibian Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...

s. 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 nu ...

s or feed on

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

s. Their

mouthparts Mouthparts may refer to: * The parts of a mouth ** Arthropod mouthparts The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired append ...

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 monophyletic lineage within the superfami ...

'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 ...

, 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 per ...

. 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 s ...

of the higher taxa of Nepomorpha were long controversial, cladistic analysis of

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 used t ...

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 gr ...

, 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 "unispe ...

with the

Aphelocheiridae ''Aphelocheirus'' is a genus of true bugs belonging to the family Aphelocheiridae. The genus was first described by Westwood in 1833. The genus has almost cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for ...

and Potamocoridae being split off in a new superfamily Aphelocheiroidea. The Cibariopectinata, a proposed

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

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 A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...

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'':

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, siltston ...

, Tithonian ~ 151 Ma.)

Nepoidea

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

Corixoidea

* Family

– water boatmen

Ochteroidea

;

Clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

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

, tentatively placed here)

Aphelocheiroidea

* Family

* Family Potamocoridae

Naucoroidea

* Family Naucoridae – creeping water bugs

Notonectoidea

* Family Notonectidae – backswimmers

Pleoidea

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 and a few from Africa, Madagascar and South America. These bugs are found swimming or walking amid submerged vegetation in stag ...

* 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

Footnotes

Further reading