Neosomy is the formation of new external structure in an active stage of an

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 ...

, in a taxon that normally only changes during

moulting In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

. It occurs in

nematodes The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...

and a wide range of

arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, oft ...

, especially those with symbiotic lifestyles. An organism that has undergone neosomy is a neosome, while a new external structure formed by neosomy is a neosomule. Neosomy is similar to

physogastrism Physogastrism or physogastry is a characteristic of certain arthropods (mostly insects and mites), where the abdomen is greatly enlarged and membranous. The most common examples are the "queens" of certain species of eusocial insects such as termit ...

(or physogastry) and the two phenomena are sometimes confused. However, physogastrism is usually defined as distension of the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the tors ...

, without the growth of new cuticle.

Examples

Acari

Larvae of some

chiggers ''Trombicula'', known as chiggers, red bugs, scrub-itch mites, or berry bugs, are small arachnids (eight-legged arthropods) in the Trombiculidae family. In their larval stage, they attach to various animals, including humans, and feed on skin, ...

can increase in size massively via neosomy, such as '' Vatacarus'' (from sea kraits) enlarging by 1500 times or more, and '' Riedlinia'' (from

bats Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...

) by up to 750 times. Other mites with neosomatic larvae include ''

Trombidium ''Trombidium'' is a genus of mite with about 30 described species. Species * '' Trombidium auroraense'' Vercammen-Grandjean, Van Driesche & Gyrisco, 1977 – New York * '' Trombidium breei'' Southcott, 1986 – Europe (host: ''Agapetes galathea ...

'', '' Eutrombidium'' and the aquatic ''

Eylais ''Eylais'' is a genus of mites belonging to the family Eylaidae. The genus has cosmopolitan distribution. Species: * '' Eylais abitibiensis'' Marshall, 1929 * '' Eylais amplipons'' Viets Biology ''Eylais'' mite larvae are ectoparasites of ...

'' and '' Hydrachna''. In ticks of family

Ixodidae The Ixodidae are the family of hard ticks or scale ticks, one of the three families of ticks, consisting of over 700 species. They are known as 'hard ticks' because they have a scutum or hard shield, which the other major family of ticks, the 'so ...

, the larvae, nymphs and adult females show neosomy. This involves an initial period where the tick thickens its cuticle and slowly gains weight, then a rapid engorgement (increasing the tick's size by as much as 100 times) that returns the cuticle to its original thickness. In the soft ticks (

Argasidae The Argasidae are the family of soft ticks, one of the three families of ticks. The family contains 193 species, although the composition of the genera is less certain, and more study is needed before the genera can become stable. The currentl ...

), neosomy usually occurs in larvae only.

Insects

Females of some

flea Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, a ...

species in superfamilies Pulicoidea, Vermipsylloidea and Malacopsylloidea are neosomatic. For example, an adult female '' Tunga monositus'' starts out at 1 mm long and, after feeding and growing, increases in volume by 1000 times, becomes circular in shape and forms anterior lobes that the head is retracted between (for protection). Similar to the aforementioned fleas,

bat flies Bat flies are members of the insect order Diptera, the true flies, which are external parasites of bats. Two families of flies are exclusively bat flies: Nycteribiidae and Streblidae. Bat flies have a cosmopolitan distribution, meaning that they ...

of genus '' Ascodipteron'' have females which attach to a host, then lose their limbs and transform into neosomes, with the head and thorax withdrawn into a swollen abdomen. K8085-21

Neosomy occurs in queen

termites Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blatt ...

and in queen

ants Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Creta ...

of certain species. Queen termites include the largest neosomes among terrestrial arthropods, with some exceeding 12.5 cm in length. Termite-associated species of phorid flies and

rove beetles The rove beetles are a family (Staphylinidae) of beetles, primarily distinguished by their short elytra (wing covers) that typically leave more than half of their abdominal segments exposed. With roughly 63,000 species in thousands of genera, th ...

have neosomatic females. In rove beetles, some genera have neosomatic males as well as females, and neosomy in some genera results in an abdomen that resembles a termite.

Crustaceans

Parasitic

copepods Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...

, such as ''

Lernaea ''Lernaea'' is a genus of copepod crustaceans whose members are commonly called ''anchor worms'' and are parasitic on freshwater fishes. Life cycle Anchor worms mate during the last free-swimming (copepodid) stage of development. After mating, th ...

'', '' Collipravus'', and '' Lernaeenicus'', exhibit neosomy. In some of the more extreme instances, neosomes vary greatly in shape within a species.

Purposes

Neosomy is a mechanism that allows a symbiote to better exploit abundant food. It increases the reproductive potential of females. For example, a female ixodid tick can usually lay thousands of eggs at once, compared to the few hundred eggs of a female non-neosomatic argasid. There are also other possible purposes. In '' Termitomimus'' and '' Nasutimimus'' rove beetles, the abdomen is similar in shape to a termite nymph and may be used in tactile

mimicry In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. Often, mimicry ...

.{{Cite journal , last=Kistner , first=David H. , date=1968 , title=Revision of the African Species of the Termitophilous Tribe Corotocini (Coleoptera, Staphylinidae) II. The Genera Termitomimus Tragardh and Nasutimimus New Genus and Their Relationships , url=https://www.jstor.org/stable/3999251 , journal=The Coleopterists Bulletin , volume=22 , issue=3 , pages=65–93 , issn=0010-065X

References

Animal developmental biology