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 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. 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 regions, 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 appropriate s ...

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-l ...

. 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

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 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 ou ...

, 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 th ...

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 scorpion Nepidae is a family of exclusively aquatic Heteropteran insects in the order Hemiptera. They are commonly called water scorpions for their superficial resemblance to scorpions, due to their raptorial forelegs and the presence of a long slender p ...

s (Nepidae) and

giant water bug Belostomatidae is a family of freshwater hemipteran insects known as giant water bugs or colloquially as toe-biters, Indian toe-biters, electric-light bugs, alligator ticks, or alligator fleas (in Florida). They are the largest insects in the ord ...

s (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% of ...

and amphibians. Others are omnivores 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 exclu ...

s. Their mouthparts form a

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

as in all Heteroptera and most Hemiptera. With this, they pierce their food source to suck out fluids; some, like the Corixidae, 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 ''Notonecta glauca'' (common backswimmer) is a species of aquatic insect, and a type of backswimmer. This species is found in large parts of Europe, North Africa, and east through Asia to Siberia and China. In much of its range it is the most com ...

'') of the

Notonectidae Notonectidae is a cosmopolitan family of aquatic insects in the order Hemiptera, commonly called backswimmers because they swim "upside down" (inverted). They are all predators and typically range from in length. They are similar in appearance t ...

can easily pierce the skin of humans and deliver a wound often more painful than a bee'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 un ...

, 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 (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

. 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 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 nam ...

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 chara ...

of mitochondrial 16S and 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 calle ...

data and

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

has more recently resolved to near-perfection. The long-accepted superfamilies are all monophyletic, with the exception of the

Naucoroidea 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 the ...

, 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 and Potamocoridae being split off in a new superfamily

Aphelocheiroidea 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 ou ...

. 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

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, Tithonian ~ 151 Ma.)

Nepoidea 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 ou ...

* Family

Belostomatidae Belostomatidae is a family of freshwater hemipteran insects known as giant water bugs or colloquially as toe-biters, Indian toe-biters, electric-light bugs, alligator ticks, or alligator fleas (in Florida). They are the largest insects in the or ...

– giant water bugs * Family

Nepidae Nepidae is a family of exclusively aquatic Heteropteran insects in the order Hemiptera. They are commonly called water scorpions for their superficial resemblance to scorpions, due to their raptorial forelegs and the presence of a long slender p ...

– water scorpions

Corixoidea

* Family Corixidae – water boatmen

Ochteroidea 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 ou ...

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

, tentatively placed here)

Aphelocheiroidea 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 ou ...

* Family Aphelocheiridae * Family Potamocoridae

Naucoroidea 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 the ...

* Family Naucoridae – creeping water bugs

Notonectoidea

* Family

– 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 ou ...

Note: sometimes included in Notonectoidea * Family Helotrephidae * Family Pleidae – pygmy backswimmers

Systematics

Nepoidea 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 ou ...

Corixoidea

Ochteroidea 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 ou ...

Aphelocheiroidea 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 ou ...

Naucoroidea 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 the ...

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 ou ...

Footnotes

Further reading