larva

{{Short description|Juvenile form of distinct animals before metamorphosis}}

{{Other uses}}

File:Papilio xuthus Larva 2011-10-15.jpg butterfly]]

File:Eurosta solidaginis larva.jpg goldenrod gall fly larva]]

A larva ({{IPAc-en|'|l|ɑr|v|ə|}}; {{plural form}}: larvae {{IPAc-en|'|l|ɑr|v|iː|}}) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase of their life cycle.

A larva's appearance is generally very different from the adult form (e.g. caterpillars and butterflies) including different unique structures and organs that do not occur in the adult form. Their diet may also be considerably different. In the case of smaller primitive arachnids, the larval stage differs by having three instead of four pairs of legs.{{cite web|url= https://dec.alaska.gov/eh/vet/ticks/tick-identification/#:~:text=Additionally%2C%20ticks%20go%20through%20three,of%20a%20grain%20of%20sand. | title= TICK IDENTIFICATION | date= 4 October 2024|work=Division of environmental health}}

Larvae are frequently adapted to different environments than adults. For example, some larvae such as tadpoles live almost exclusively in aquatic environments, but can live outside water as adult frogs. By living in a distinct environment, larvae may be given shelter from predators and reduce competition for resources with the adult population.

Animals in the larval stage will consume food to fuel their transition into the adult form. In some organisms like polychaetes and barnacles, adults are immobile but their larvae are mobile, and use their mobile larval form to distribute themselves.{{Citation|last=Qian|first=Pei-Yuan|title=Larval settlement of polychaetes|date=1999|work=Reproductive Strategies and Developmental Patterns in Annelids|pages=239–253|place=Dordrecht|publisher=Springer Netherlands|doi=10.1007/978-94-017-2887-4_14|isbn=978-90-481-5340-4}}{{Cite journal|last1=Chen|first1=Zhang-Fan|last2=Zhang|first2=Huoming|last3=Wang|first3=Hao|last4=Matsumura|first4=Kiyotaka|last5=Wong|first5=Yue Him|last6=Ravasi|first6=Timothy|last7=Qian|first7=Pei-Yuan|date=2014-02-13 |title=Quantitative Proteomics Study of Larval Settlement in the Barnacle Balanus amphitrite |journal=PLOS ONE |language=en |volume=9 |issue=2 |pages=e88744 |doi=10.1371/journal.pone.0088744 |pmid=24551147 |pmc=3923807|bibcode=2014PLoSO...988744C|issn=1932-6203 |doi-access=free}} These larvae used for dispersal are either planktotrophic (feeding) or lecithotrophic (non-feeding).

Some larvae are dependent on adults to feed them. In many eusocial Hymenoptera species, the larvae are fed by female workers. In Ropalidia marginata (a paper wasp) the males are also capable of feeding larvae but they are much less efficient, spending more time and getting less food to the larvae.{{cite journal|last1=Sen|first1=R|last2=Gadagkar|first2=R|title=Males of the social wasp Ropalidia marginata can feed larvae, given an opportunity|journal=Animal Behaviour|date=2006|volume=71|issue=2|pages=345–350|doi=10.1016/j.anbehav.2005.04.022|s2cid=39848913}}

The larvae of some organisms (for example, some newts) can become pubescent and do not develop further into the adult form. This is a type of neoteny.{{Cite journal|last=Wakahara|first=Masami|date=1996|title=Heterochrony and Neotenic Salamanders: Possible Clues for Understanding the Animal Development and Evolution|journal=Zoological Science|volume=13|issue=6|pages=765–776|doi=10.2108/zsj.13.765|doi-broken-date=1 November 2024 |pmid=9107136|s2cid=35101681|issn=0289-0003}}

It is a misunderstanding that the larval form always reflects the group's evolutionary history. This could be the case, but often the larval stage has evolved secondarily, as in insects.{{Citation|last1=Nagy|first1=Lisa M.|title=Cell Lineages in Larval Development and Evolutions of Holometabolous Insects|date=1999|work=The Origin and Evolution of Larval Forms|pages=275–300|publisher=Elsevier|isbn=978-0-12-730935-4|last2=Grbić|first2=Miodrag|doi=10.1016/b978-012730935-4/50010-9}}{{Cite journal|last=Raff|first=Rudolf A|date=2008-01-11|title=Origins of the other metazoan body plans: the evolution of larval forms|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=363|issue=1496|pages=1473–1479|doi=10.1098/rstb.2007.2237|pmid=18192188|issn=0962-8436|pmc=2614227}} In these cases{{clarify|reason=Please specify in which of the two types of cases|date=February 2024}}, the larval form may differ more than the adult form from the group's common origins.{{cite journal |last1=Williamson |first1=Donald I. |author-link=Donald I. Williamson|date=2006 |title=Hybridization in the evolution of animal form and life-cycle |journal=Zoological Journal of the Linnean Society |volume=148 |issue= 4|pages=585–602 |doi= 10.1111/j.1096-3642.2006.00236.x|doi-access=free }}

Selected types of larvae

class="wikitable sortable"

! Animal

Name of larvae
Porifera (sponges)coeloblastula (= blastula, amphiblastula), parenchymula (= parenchymella, stereogastrula)
HeterocyemidaWagener's larva
Dicyemidainfusoriform larva
Cnidariansplanula (= stereogastrula), actinula
Ctenophoracydippid larvae
PlatyhelminthesTurbellaria: Müller's larva, Götte's larva;
Trematoda: miracidium, sporocyst, redia, cercaria;
Monogenea: oncomiracidium;
Cestoda: cysticercus, cysticercoid, oncosphere (or hexacanth), coracidium, plerocercoid
Annelidanectochaete, polytroch
NematodaDauer larva, microfilaria
Sipunculapelagosphera larva
Ectoproctacyphonautes, vesiculariform larvae
Nematomorphanematomorphan larva
Phoronidsactinotroch
Cycliophorapandora, chordoid larva
Nemerteapilidium, Iwata larva, Desor larva
Acanthocephalaacanthor
LociferaHiggins larva
Brachiopodalobate larva
Priapulaloricate larva
Certain molluscs, annelids, nemerteans and sipunculidstrochophore
Certain molluscsveliger
Mollusca: freshwater Bivalvia (mussels)glochidium
Arthropoda: †Trilobitaprotaspis (unjointed), meraspis (increasing number of joints, but 1 less than the holaspis), holaspis (=adult){{cite book|last= Moore|first= R.C.|year= 1959|title= Arthropoda I – Arthropoda General Features, Proarthropoda, Euarthropoda General Features, Trilobitomorpha|publisher= Geological Society of America/University of Kansas Press|series= Treatise on Invertebrate Paleontology|volume= Part O.|pages= O121, O122, O125|location= Boulder, Colorado/Lawrence, Kansas|isbn= 978-0-8137-3015-8}}
Arthropoda: Xiphosuraeuproöps larva ("trilobite larva")
Arthropoda: Pycnogonidaprotonymphon
CrustaceansGeneral: nauplius, metanauplius, protozoea, antizoea, pseudozoea, zoea, postlarva, cypris, primary larva, mysis
Decapoda: zoea
Rhizocephala: kentrogon
Insecta: Lepidoptera (butterflies and moths)caterpillar
Insecta: Beetlesgrub
Insecta: Flies, Bees, Waspsmaggot
Insecta: Mosquitoeswriggler
Insecta: Orthoptera (crickets and grasshoppers), Odonata (dragonflies and damselflies), Hemiptera (true bugs)nymph
Deuterostomesdipleurula (hypothetical larva)
Echinodermatabipinnaria, vitellaria, brachiollaria, pluteus, ophiopluteus, echinopluteus, auricularia
Hemichordatatornaria
Urochordatatadpole (does not feed, technically a "swimming embryo")
Fish (generally)Ichthyoplankton
Fish: Petromyzontiformes (lamprey)ammocoete
Fish: Anguilliformes (eels)leptocephalus
Amphibianstadpole, polliwog

Insect larvae

File:Hercules beetle (larva).jpg (Dynastes hercules) are among the largest of any species of insect]]

File:Micromus.aphids.2.jpg sp.]]

Within Insects, only Endopterygotes show complete metamorphosis, including a distinct larval stage.{{Cite web|title=Division: Endopterygota – Amateur Entomologists' Society (AES)|url=https://www.amentsoc.org/insects/fact-files/orders/endopterygota.html |access-date=2020-08-03|website=www.amentsoc.org}}{{cite web |url=https://entomology.ca.uky.edu/ef017 |title=Recognizing Insect Larval Types |publisher=University of Kentucky |access-date=28 April 2016}} Several classifications have been suggested by many entomologists,{{Cite book|last=JOHNSON, NORMAN. TRIPLEHORN, CHARLES A.|title=BORROR AND DELONG'S INTRODUCTION TO THE STUDY OF INSECTS.|date=2020|publisher=CENGAGE LEARNING CUSTOM P|isbn=978-0-357-67127-6|oclc=1163940863}}{{Cite book|title=Encyclopedia of Entomology|date=2008|publisher=Springer Netherlands|isbn=978-1-4020-6242-1|editor-last=Capinera|editor-first=John L.|location=Dordrecht|doi=10.1007/978-1-4020-6359-6}} and following classification is based on Antonio Berlese classification in 1913. There are four main types of endopterygote larvae types:{{cite web |url=http://www.agriinfo.in/default.aspx?page=topic&superid=6&topicid=1552 |title=Types of Insect Larva |publisher=Agri info |access-date=28 April 2016 | archive-url=https://web.archive.org/web/20160514042749/http://www.agriinfo.in/default.aspx?page=topic&superid=6&topicid=1552 |archive-date=14 May 2016 |url-status=dead }}{{Cite web|date=2017-03-23|title=Types of Insect Larva|url=https://agriinfo.in/types-of-insect-larva-1531/|access-date=2021-11-22|website=agriinfo.in|language=en-US|archive-date=2017-02-04|archive-url=https://web.archive.org/web/20170204080237/http://www.agriinfo.in/default.aspx?page=topic&superid=6&topicid=1552|url-status=dead}}

  1. Apodous larvae – no legs at all and are poorly sclerotized. Based on sclerotization. All Apocrita are apodous. Three apodous forms are recognized.
  2. * Eucephalous – with well sclerotized head capsule. Found in Nematocera, Buprestidae and Cerambycidae families.
  3. * Hemicephalus – with a reduced head capsule, retractable in to the thorax. Found in Tipulidae and Brachycera families.
  4. * Acephalus – without head capsule. Found in Cyclorrhapha
  5. Protopod larvae – larva have many different forms and often unlike a normal insect form. They hatch from eggs which contain very little yolk. E.g. first instar larvae of parasitic hymenoptera.
  6. Polypod larvae – also known as eruciform larvae, these larvae have abdominal prolegs, in addition to usual thoracic legs. They are poorly sclerotized and relatively inactive. They live in close contact with their food. Best example is caterpillars of lepidopterans.
  7. Oligopod larvae – have well-developed head capsule and mouthparts are similar to the adult, but without compound eyes. They have six legs. No abdominal prolegs. Two types can be seen:
  8. * Campodeiform – well sclerotized, dorso-ventrally flattened body. Usually long legged predators with prognathous mouthparts. (lacewing, trichopterans, mayflies and some coleopterans).
  9. * Scarabeiform – poorly sclerotized, flat thorax and abdomen. Usually short legged and inactive burrowing forms. (Scarabaeoidea and other coleopterans).

See also

References

{{Reflist}}

Bibliography

  • Brusca, R. C. & Brusca, G. J. (2003). Invertebrates (2nd ed.). Sunderland, Mass. : Sinauer Associates.
  • Hall, B. K. & Wake, M. H., eds. (1999). The Origin and Evolution of Larval Forms. San Diego: Academic Press.
  • Leis, J. M. & Carson-Ewart, B. M., eds. (2000). The Larvae of Indo-Pacific Coastal Fishes. An Identification Guide to Marine Fish Larvae''. Fauna Malesiana handbooks, vol. 2. Brill, Leiden.
  • Minelli, A. (2009). The larva. In: Perspectives in Animal Phylogeny and Evolution. Oxford University Press. p. 160–170. [https://books.google.com/books?id=jIASDAAAQBAJ link].
  • Shanks, A. L. (2001). An Identification Guide to the Larval Marine Invertebrates of the Pacific Northwest. Oregon State University Press, Corvallis. 256 pp.
  • Smith, D. & Johnson, K. B. (1977). A Guide to Marine Coastal Plankton and Marine Invertebrate Larvae. Kendall/Hunt Plublishing Company.
  • Stanwell-Smith, D., Hood, A. & Peck, L. S. (1997). A field guide to the pelagic invertebrates larvae of the maritime Antarctic. British Antarctic Survey, Cambridge.
  • Thyssen, P.J. (2010). [https://www.springer.com/cda/content/document/cda_downloaddocument/9781402096839-c2.pdf?SGWID=0-0-45-1118144-p173877432 Keys for Identification of Immature Insects] {{Webarchive|url=https://web.archive.org/web/20170809221659/https://www.springer.com/cda/content/document/cda_downloaddocument/9781402096839-c2.pdf?SGWID=0-0-45-1118144-p173877432 |date=2017-08-09 }}. In: Amendt, J. et al. (ed.). Current Concepts in Forensic Entomology, chapter 2, pp. 25–42. Springer: Dordrecht.