Crustacean larva

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Larval and adult prawns
Nauplius larva
Adult Penaeus monodon

Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The larvae of crustaceans often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults (on the sea bed), more-so than where the larvae are planktonic, and thereby easily caught.

Many crustacean larvae were not immediately recognised as larvae when they were discovered, and were described as new genera and species. The names of these genera have become generalised to cover specific larval stages across wide groups of crustaceans, such as zoea and nauplius. Other terms described forms which are only found in particular groups, such as the glaucothoe of hermit crabs, or the phyllosoma of slipper lobsters and spiny lobsters.

Life cycle

At its most complete, a crustacean's life cycle begins with an

egg, which is usually fertilised, but may instead be produced by parthenogenesis. This egg hatches into a pre-larva or pre-zoea. Through a series of moults, the young animal then passes through various zoea stages, followed by a megalopa or post-larva. This is followed by metamorphosis into an immature form, which broadly resembles the adult, and after further moults, the adult form is finally reached. Some crustaceans continue to moult as adults, while for others, the development of gonads
signals the final moult.

Any organs which are absent from the adults do not generally appear in the larvae, although there are a few exceptions, such as the

pleopods in certain Anomura and crabs.[1] In a more extreme example, the Sacculina and other Rhizocephala
have a distinctive nauplius larva with its complex body structure, but the adult form lacks many organs due to extreme adaptation to its parasitic life style.

Cyclops (Copepoda)
Nauplius
Adult

History of the study of crustacean larva

Palaemonetes vulgaris in 1879).[1]

Larval stages

Anatomy of nauplii
Ventral view of a Tetraclita nauplius, showing cephalic appendages
Close-up of an adult Triops (Notostraca), showing a persistent naupliar eye between the two compound eyes

Nauplius

The genus name Nauplius was published posthumously by

isopods being one example.[5]

Zoea

The genus Zoea was initially described by Louis Augustin Guillaume Bosc in 1802 for an animal now known to be the larva of a crab.[1] The zoea stage (plural: zoeas or zoeae), only found in members of Malacostraca,[5] is characterised by the use of the thoracic appendages for swimming and a large dorsal spine.[5]

Post-larva

The post-larva or Megalopae, also found exclusively in the Malacostraca,[5] is characterised by the use of abdominal appendages (pleopods) for propulsion. The post-larva is usually similar to the adult form, and many names have been erected for this stage in different groups. William Elford Leach erected the genus Megalopa in 1813 for a post-larval crab; a copepod post-larva is called a copepodite; a barnacle post-larva is called a cypris; a shrimp post-larva is called a parva; a hermit crab post-larva is called a glaucothoe; a spiny lobster / furry lobsters post-larva is called a puerulus and a slipper lobster post-larva is called a nisto.

Larvae of crustacean groups

Branchiopoda

In the Branchiopoda, the offspring hatch as a nauplius or metanauplius larva.[6]

Cephalocarida

In the Mediterranean horseshoe shrimp Lightiella magdalenina, the young experience 15 stages following the nauplius, termed metanaupliar stages, and two juvenile stages, with each of the first six stages adding two trunk segments, and the last four segments being added singly.[7]

Remipedia

The larvae of

Euphausiacea (krill) has been used to suggest a link between Remipedia and Malacostraca.[8]

Malacostraca

Amphipod hatchlings resemble the adults.[9]

Young isopod crustaceans hatch directly into a manca stage, which is similar in appearance to the adult. The lack of a free-swimming larval form has led to high rates of endemism in isopods, but has also allowed them to colonise the land, in the form of the woodlice.

Stomatopoda

The larvae of many groups of

Squilloidea, a pseudozoea larva develops into an alima larva, while in Gonodactyloidea, a pseudozoea develops into an erichthus.[10]

A single

Solnhofen lithographic limestone.[11]

A nauplius of Euphausia pacifica hatching, emerging backwards from the egg

Krill

Main article: Krill § Life history and behavior

The life cycle of krill is relatively well understood, although there are minor variations in detail from species to species. After hatching, the larvae go through several stages called nauplius, pseudometanauplius, metanauplius, calyptopsis and furcilia stages, each of which is sub-divided into several sub-stages. The pseudometanauplius stage is exclusive to the so-called "sac-spawners". Until the metanauplius stage, the larvae are reliant on the yolk reserves, but from the calyptopsis stage, they begin to feed on phytoplankton. During the furcilia stages, segments with pairs of swimmerets are added, beginning at the frontmost segments, with each new pair only becoming functional at the next moult. After the final furcilia stage, the krill resembles the adult.

Orconectes obscurus crayfish
: such large eggs are often indicative of abbreviated development.

Decapoda

"Puerulus" redirects here. For the genus of whip lobsters, see Puerulus (crustacean).
European lobster

Apart from the prawns of the suborder

egg yolk (lecithotrophy). In species with normal development, eggs are roughly 1% of the size of the adult; in species with abbreviated development, and therefore more yolk in the eggs, the eggs may reach 1/9 of the adult's size.[1]

The post-larva of shrimp is called parva, after the species Acanthephyra parva described by Henri Coutière, but which was later recognised as the larva of Acanthephyra purpurea.[12]

In the marine lobsters, there are three larval stages, all similar in appearance.

pleopods.[1]

A phyllosoma larva of the spiny lobster Palinurus elephas, from Ernst Haeckel's Kunstformen der Natur

The larvae of the Achelata (slipper lobsters, spiny lobsters and furry lobsters) are unlike any other crustacean larvae. The larvae are known as phyllosoma, after the genus Phyllosoma erected by William Elford Leach in 1817. They are flattened and transparent, with long legs and eyes on long eyestalks. After passing through 8–10 phyllosoma stages, the larva undergoes "the most profound transformation at a single moult in the Decapoda", when it develops into the so-called puerulus stage, which is an immature form resembling the adult animal.[1]

The members of the traditional infraorder Thalassinidea can be divided into two groups on the basis of their larvae. According to Robert Gurney,[1] the "homarine group" comprises the families Axiidae and Callianassidae, while the "anomuran group" comprises the families Laomediidae and Upogebiidae. This split corresponds with the division later confirmed with molecular phylogenetics.[14]

Among the

Aegla, the young hatch from the eggs in the adult form.[1] Squat lobsters pass through four, or occasionally five, larval states, which have a long rostrum, and a spine on either side of the carapace; the first post-larva closely resembles the adult.[1] Porcelain crabs have two or three larval stages, in which the rostrum and the posterior spine on the carapace are "enormously long".[1] Hermit crabs pass through around four larval stages. The post-larva is known as the glaucothoe, after a genus named by Henri Milne-Edwards in 1830.[1] The glaucothoe is 3 millimetres (0.12 in) long in Pagurus longicarpus, but glaucothoe larvae up to 20 mm (0.79 in) are known, and were once thought to represent animals which had failed to develop correctly.[1] Like the preceding stages, the glaucothoe is symmetrical, and although the glaucothoe begins as a free-swimming form, it often acquires a gastropod shell to live in; the coconut crab, Birgus latro, always carries a shell when the immature animal comes ashore, but this is discarded later.[1]

Carcinus maenas (Decapoda: Brachyura)
Zoea
Juvenile

Although they are classified as crabs, the larvae of Dromiacea are similar to those of the Anomura, which led many scientists to place dromiacean crabs in the Anomura, rather than with the other crabs. Apart from the Dromiacea, all crabs share a similar and distinctive larval form. The crab zoea has a slender, curved abdomen and a forked telson, but its most striking features are the long rostral and dorsal spines, sometimes augmented by further, lateral spines.[1] These spines can be many times longer than the body of the larva. Crab prezoea larvae have been found fossilised in the stomach contents of the Early Cretaceous bony fish Tharrhias.[15]

Copepoda

Copepods have six naupliar stages, followed by a stage called the copepodid, which has the same number of body segments and appendages in all copepods. The copepodid larva has two pairs of unsegmented swimming appendages, and an unsegmented "hind-body" comprising the thorax and the abdomen.[1] There are typically five copepodid stages, but parasitic copepods may stop after a single copepodid stage. Once the gonads develop, there are no further moults.[1]

Parasitic copepods

First chalimus of Lepeophtheirus elegans Gusev, 1951 (Copepoda, Caligidae):
A, leg 3;
B, leg 3 (other specimen);
C, leg 4;
D, caudal ramus;
E, habitus of putative female, dorsal.
Scale bars: A–D = 0.025 mm; E = 0.2 mm.[16]

Chalimus (plural chalimi) is a stage of development of a copepod parasite of fish, such as the salmon louse (Lepeophtheirus salmonis).[17][18]

Chalimus Burmeister, 1834 is also a synonym for Lepeophtheirus Nordmann, 1832.

Look up Chalimus in Wiktionary, the free dictionary.

Facetotecta

The single genus in the Facetotecta, Hansenocaris, is only known from its larvae. They were first described by Christian Andreas Victor Hensen in 1887, and named "y-nauplia" by Hans Jacob Hansen, assuming them to be the larvae of barnacles.[19] The adults are presumed to be parasites of other animals.[20]

See also

References

  1. ^ a b c d e f g h i j k l m n o p q r Robert Gurney (1942). Larvae of decapod crustacea (PDF). London: Ray Society. pp. 1–306.
  2. ISBN 9780374251437
    .
  3. ^ Crustaceamorpha: Metamorphosis and Larvae - UCMP Berkeley
  4. ^ Key for the identification of crustacean nauplii - Academia.edu
  5. ^ a b c d "Crustaceamorpha: Metamorphosis and Larvae". ucmp.berkeley.edu. UC Museum of Paleontology (UCMP). Retrieved 22 August 2022.
  6. ^ Branchiopoda (Anostraca, Notostraca, Laevicaudata, Spinicaudata, Cyclestherida)
  7. S2CID 85246439
    .
  8. S2CID 11575617
    .
  9. Museum Victoria. Archived from the original
    on September 18, 2010. Retrieved June 7, 2010.
  10. ^ S. T. Ahyong; J. K. Lowry. "Stomatopoda: Families". World Crustacea. Australian Museum. Archived from the original on December 14, 2010. Retrieved June 6, 2010.
  11. ^ Joachim T. Haug; Carolin Haug; Manfred Ehrlich (2008). "First fossil stomatopod larva (Arthropoda: Crustacea) and a new way of documenting Solnhofen fossils (Upper Jurassic, Southern Germany)" (PDF). Palaeodiversity. 1: 103–109.
  12. doi:10.1111/j.1096-3642.1907.tb00072.x
    .
  13. doi:10.1006/zjls.1995.0011
    .
  14. Raffles Bulletin of Zoology. Suppl. 21: 1–109. Archived from the original
    (PDF) on 2011-06-06.
  15. ^ John G. Maisey & Maria da Gloria P. de Carvalho (1995). "First records of fossil sergestid decapods and fossil brachyuran crab larvae (Arthropoda, Crustacea), with remarks on some supposed palaemonid fossils, from the Santana Formation (Aptian-Albian, NE Brazil)" (PDF). American Museum Novitates (3132): 1–20.
  16. PMID 23647664. Open access icon
  17. ^ The salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) life cycle has only two chalimus stages. LA Hamre, C Eichner, CMA Caipang, ST Dalvin…, PLOS One, 2013
  18. ^ Ultrastructure of the frontal filament in chalimus larvae of Caligus elongatus and Lepeophtheirus salmonis from Atlantic salmon, Salmo salar. AW Pike, K Mackenzie, A Rowand, Pathogens of wild and farmed fish: sea lice, 1993
  19. S2CID 2943845
    .
  20. PMID 18598383
    .
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