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 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 ...
, in which the hard
exoskeleton
An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...
is shed to allow the animal to grow. The
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
...
e of
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
s 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
plankton
Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...
ic, 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 crab
Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an as ...
s, or the ''
phyllosoma'' of
slipper lobsters and
spiny lobster
Spiny lobsters, also known as langustas, langouste, or rock lobsters, are a family (Palinuridae) of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are also, especially in Australia, New Zealand, Ireland, So ...
s.
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
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...
. 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
Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
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
gonad
A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...
s 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
vestige
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
of the fourth
pereiopod
The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in variou ...
in the larvae of ''
Lucifer
Lucifer is one of various figures in folklore associated with the planet Venus. The entity's name was subsequently absorbed into Christianity as a name for the devil. Modern scholarship generally translates the term in the relevant Bible passa ...
'', and some
pleopod
The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in variou ...
s in certain
Anomura and
crab
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...
s.
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.
History of the study of crustacean larva
Antonie van Leeuwenhoek
Antonie Philips van Leeuwenhoek ( ; ; 24 October 1632 – 26 August 1723) was a Dutch microbiologist and microscopist in the Golden Age of Dutch science and technology. A largely self-taught man in science, he is commonly known as " the ...
was the first person to observe the difference between larval crustaceans and the adults when he watched the eggs of ''
Cyclops
In Greek mythology and later Roman mythology, the Cyclopes ( ; el, Κύκλωπες, ''Kýklōpes'', "Circle-eyes" or "Round-eyes"; singular Cyclops ; , ''Kýklōps'') are giant one-eyed creatures. Three groups of Cyclopes can be distinguish ...
'' hatching in 1699.
Despite this, and other observations over the following decades, there was controversy among scientists about whether or not
metamorphosis
Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
occurred in crustaceans, with conflicting observations presented, based on different species, some of which went through a metamorphosis, and some of which did not. In 1828
John Vaughan Thompson published a paper "On the Metamorphoses of the Crustacea, and on Zoea, exposing their singular structure and demonstrating they are not, as has been supposed, a peculiar Genus but the Larva of Crustacea!!" However his work was not believed due to crayfish not undergoing metamorphosis. This controversy persisted until the 1840s, and the first descriptions of a complete series of larval forms were not published until the 1870s (
Sidney Irving Smith
Sidney Irving Smith (February 18, 1843 in Norway, Maine – May 6, 1926 in New Haven, Connecticut) was an American zoologist.
Private life
Sidney Smith was the son of Elliot Smith and Lavinia Barton. His brother in law was Addison Emery Verrill. ...
on the
American lobster
The American lobster (''Homarus americanus'') is a species of lobster found on the Atlantic coast of North America, chiefly from Labrador to New Jersey. It is also known as Atlantic lobster, Canadian lobster, true lobster, northern lobster, Can ...
in 1873;
Georg Ossian Sars
Prof Georg Ossian Sars HFRSE (20 April 1837 – 9 April 1927) was a Norwegian marine and freshwater biologist.
Life
Georg Ossian Sars was born on 20 April 1837 in Kinn, Norway (now part of Flora), the son of Pastor Michael Sars and Maren ...
on the
European lobster in 1875, and
Walter Faxon on the shrimp ''
Palaemonetes vulgaris'' in 1879).
Larval stages
Nauplius
The genus name ''Nauplius'' was published posthumously by
Otto Friedrich Müller
Otto Friedrich Müller, also known as Otto Friedrich Mueller (2 November 1730 – 26 December 1784) was a Danish naturalist and scientific illustrator.
Biography
Müller was born in Copenhagen. He was educated for the church, became tutor to a ...
in 1785 for animals now known to be the larvae of
copepod
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 ...
s. The nauplius stage (plural: ''nauplii'') is characterised by consisting of only three head segments, which are covered by a single
carapace
A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...
. The posterior body, when present, is unsegmented. Each head segment has a pair of
appendage
An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body.
In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including ante ...
s; the
antennules, antennae, and
mandibles. This larval stage has various lifestyles; some are benthic while others are swimmers, some are feeding while others are non-feeders (
lecithotrophic). The nauplius is also the stage at which a simple, unpaired eye is present. The eye is known for that reason as the "naupliar eye", and is often absent in later developmental stages, although it is retained into the adult form in some groups, such as the
Notostraca. Some crustacean groups lack this larval type,
isopod
Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and ...
s being one example.
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
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...
.
The zoea stage (plural: ''zoeas'' or ''zoeae''), only found in members of
Malacostraca
Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobs ...
,
is characterised by the use of the
thoracic
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
appendages for swimming and a large dorsal spine.
Post-larva
The post-larva or ''Megalopae'', also found exclusively in the Malacostraca,
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
William Elford Leach FRS (2 February 1791 – 25 August 1836) was an English zoologist and marine biologist.
Life and work
Elford Leach was born at Hoe Gate, Plymouth, the son of an attorney. At the age of twelve he began a medical appre ...
erected the genus ''Megalopa'' in 1813 for a post-larval crab; a
copepod
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 ...
post-larva is called a ''copepodite''; a
barnacle
A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosiv ...
post-larva is called a ''cypris''; a
shrimp
Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...
post-larva is called a ''parva''; a
hermit crab
Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an as ...
post-larva is called a ''glaucothoe''; a
spiny lobster
Spiny lobsters, also known as langustas, langouste, or rock lobsters, are a family (Palinuridae) of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are also, especially in Australia, New Zealand, Ireland, So ...
/
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 most basal group of crustaceans, there is no metamorphosis; instead, the animal grows through a series of moults, with each moult adding various numbers of segments to the body, but without any dramatic changes in form. Every other crustacean group with free larvae shows a
metamorphosis
Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
, and this difference in the larvae is thought to reflect "a fundamental cleavage" of the crustaceans.
Cephalocarida
In the
Mediterranean
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
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.
Remipedia
The larvae of
remipedes
Remipedia is a class of blind crustaceans found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, and the Atlantic Ocean. The ...
are
lecithotrophic, consuming
egg yolk
Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example be ...
rather than using external food sources. This characteristic, which is shared with
malacostracan groups such as the
Decapoda
The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is estim ...
and
Euphausiacea (krill) has been used to suggest a link between Remipedia and Malacostraca.
Malacostraca
Amphipod hatchlings resemble the adults.
Young
isopod
Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, and ...
crustaceans hatch directly into a ''
manca
The manca (plural: ''mancae'') is the post-larval juvenile in some crustaceans. The manca stage is the defining characteristic of a clade called Mancoida which comprises all the member of the Peracarida except the Amphipoda. Mancae closely resembl ...
'' stage, which is similar in appearance to the adult. The lack of a free-swimming larval form has led to high rates of
endemism
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...
in isopods, but has also allowed them to colonise the land, in the form of the
woodlice
A woodlouse (plural woodlice) is an isopod crustacean from the polyphyleticThe current consensus is that Oniscidea is actually triphyletic suborder Oniscidea within the order Isopoda. They get their name from often being found in old wood ...
.
Stomatopoda
The larvae of many groups of
mantis shrimp
Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 340 million years ago. Mantis shrimp typically grow to around in length, ...
are poorly known. In the superfamily
Lysiosquilloidea, the larvae hatch as ''antizoea'' larvae, with five pairs of thoracic appendages, and develop into ''erichthus'' larvae, where the pleopods appear. In the
Squilloidea, a ''pseudozoea'' larva develops into an ''alima'' larva, while in
Gonodactyloidea, a ''pseudozoea'' develops into an ''erichthus''.
A single
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 ...
stomatopod larva has been discovered, in the
Upper Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987.
In European lithostratigraphy, the name ...
Solnhofen
Solnhofen is a municipality in the district of Weißenburg-Gunzenhausen in the region of Middle Franconia in the ' of Bavaria in Germany. It is in the Altmühl valley.
The local area is famous in geology and palaeontology for Solnhofen limes ...
lithographic limestone
Lithographic limestone is hard limestone that is sufficiently fine-grained, homogeneous and defect free to be used for lithography.
Geologists use the term "lithographic texture" to refer to a grain size under 1/250 mm.
The term "sublithog ...
.
Krill
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
Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...
reserves, but from the ''calyptopsis'' stage, they begin to feed on
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
. 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.
Decapoda
![Homarus gammarus zoea](https://upload.wikimedia.org/wikipedia/commons/a/af/Homarus_gammarus_zoea.jpg)
Apart from the prawns of the suborder
Dendrobranchiata
Dendrobranchiata is a suborder of Decapoda, decapods, commonly known as prawns. There are 540 extant species in seven families, and a fossil record extending back to the Devonian. They differ from related animals, such as Caridea and Stenopodidea ...
, all decapod crustaceans brood their eggs on the female's pleopods. This has resulted in development in decapod crustaceans being generally abbreviated.
There are at most nine larval stages in decapods, as in
krill
Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian
Norwegian, Norwayan, or Norsk may refer to:
*Something of, from, or related to Norway, a country in n ...
, and both decapod nauplii and krill nauplii often lack
mouthparts and survive on nutrients supplied in the
egg yolk
Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example be ...
(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.
The post-larva of
shrimp
Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...
is called ''parva'', after the species ''Acanthephyra parva'' described by
Henri Coutière François Louis Henri Coutière (4 March 1869 in Saulzet – 23 August 1952 in Orvilliers) was a French zoologist, who specialized in the field of carcinology (crustaceans).
In 1895 he received his bachelor's degree in natural sciences, and du ...
, but which was later recognised as the larva of ''
Acanthephyra purpurea''.
In the marine
lobster
Lobsters are a family (biology), family (Nephropidae, Synonym (taxonomy), synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs ...
s, there are three larval stages, all similar in appearance.
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 include ...
crayfish
Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as crawfish, craydids, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, rock lobsters, mu ...
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
s differ from those of other crustaceans in having 40
ectoteloblast cells, rather than around 19. The larvae show abbreviated development, and hatch with a full complement of adult appendages with the exceptions of the
uropod
Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion.
Definition
Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...
s and the first pair of
pleopod
The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in variou ...
s.
![Haeckel_Phyllosoma](https://upload.wikimedia.org/wikipedia/commons/7/72/Haeckel_Phyllosoma.jpg)
The larvae of the
Achelata
The Achelata is an infra-order of the decapod crustaceans, holding the spiny lobsters, slipper lobsters and their fossil relatives.
Description
The name "Achelata" derives from the fact that all the members of this group lack the chelae (claw ...
(
slipper lobsters,
spiny lobster
Spiny lobsters, also known as langustas, langouste, or rock lobsters, are a family (Palinuridae) of about 60 species of achelate crustaceans, in the Decapoda Reptantia. Spiny lobsters are also, especially in Australia, New Zealand, Ireland, So ...
s and
furry lobsters) are unlike any other crustacean larvae. The larvae are known as ''
phyllosoma'', after the genus ''Phyllosoma'' erected by
William Elford Leach
William Elford Leach FRS (2 February 1791 – 25 August 1836) was an English zoologist and marine biologist.
Life and work
Elford Leach was born at Hoe Gate, Plymouth, the son of an attorney. At the age of twelve he began a medical appre ...
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.
The members of the traditional infraorder
Thalassinidea
Thalassinidea is a former infraorder of decapod crustaceans that live in burrows in muddy bottoms of the world's oceans. In Australian English, the littoral thalassinidean ''Trypaea australiensis'' is referred to as the ''yabby'' (a term which al ...
can be divided into two groups on the basis of their larvae. According to
Robert Gurney
Robert Gurney (31 July 1879 – 5 March 1950) was a British zoologist from the Gurney family, most famous for his monographs on ''British Freshwater Copepoda'' (1931–1933) and the ''Larvae of Decapod Crustacea'' (1942). He was not affiliated w ...
,
the "homarine group" comprises the families
Axiidae
Axiidae is a family of thalassinidean crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, ...
and
Callianassidae, while the "anomuran group" comprises the families
Laomediidae
Laomediidae is a family of crustaceans belonging to the infraorder Gebiidea
Gebiidea is an infraorder of decapod crustaceans. Gebiidea and Axiidea are divergent infraoders of the former infraorder Thalassinidea. These infraorders have conver ...
and
Upogebiidae
Upogebiidae is a family of mud shrimp crustaceans belonging to the infraorder Gebiidea
Gebiidea is an infraorder of decapod crustaceans. Gebiidea and Axiidea are divergent infraoders of the former infraorder Thalassinidea. These infraorder ...
. This split corresponds with the division later confirmed with
molecular phylogenetics
Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
.
Among the
Anomura, there is considerable variation in the number of larval stages. In the
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
n
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 include ...
genus ''
Aegla
The Aeglidae are a family of freshwater crustaceans currently restricted to South America. They are the only anomurans to be found in fresh water except for a single hermit crab species, '' Clibanarius fonticola'', on Espiritu Santo, Vanuatu
...
'', the young hatch from the eggs in the adult form.
Squat lobster
Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the cephalothorax. They are found in the two superfamilies Galatheoidea and Chirostyloidea, which form part of the decapod infraorder Anomura, alongside ...
s pass through four, or occasionally five, larval states, which have a long
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 ...
, and a spine on either side of the
carapace
A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...
; the first post-larva closely resembles the adult.
Porcelain crab
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They have flattened bodies as an adaptation for living in rock crevices. They are delicate, readily losing limbs when attack ...
s have two or three larval stages, in which the rostrum and the posterior spine on the carapace are "enormously long".
Hermit crab
Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an a ...
s pass through around four larval stages. The post-larva is known as the ''glaucothoe'', after a genus named by
Henri Milne-Edwards
Henri Milne-Edwards (23 October 1800 – 29 July 1885) was an eminent French zoologist.
Biography
Henri Milne-Edwards was the 27th child of William Edwards, an English planter and colonel of the militia in Jamaica and Elisabeth Vaux, a Frenchw ...
in 1830.
The glaucothoe is long in ''
Pagurus longicarpus
''Pagurus longicarpus'', the long-wristed hermit crab, is a common hermit crab found along the Atlantic and Gulf coasts of the United States and the Atlantic coast of Canada.Young, A. M. 1978. Desiccation tolerances for three hermit crab species ...
'', but glaucothoe larvae up to are known, and were once thought to represent animals which had failed to develop correctly.
Like the preceding stages, the glaucothoe is symmetrical, and although the glaucothoe begins as a free-swimming form, it often acquires a
gastropod shell
The gastropod shell is part of the body of a Gastropoda, gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium s ...
to live in; the
coconut crab
The coconut crab (''Birgus latro'') is a species of terrestrial hermit crab, also known as the robber crab or palm thief. It is the largest terrestrial arthropod in the world, with a weight of up to . It can grow to up to in width from the tip ...
, ''Birgus latro'', always carries a shell when the immature animal comes ashore, but this is discarded later.
Although they are classified as
crab
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...
s, the larvae of
Dromiacea
Dromiacea is a group of crabs, ranked as a section. It contains 240 extant and nearly 300 extinct species. Dromiacea is the most basal grouping of Brachyura crabs, diverging the earliest in the evolutionary history, around the Late Triassic or ...
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
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 torso. ...
and a forked
telson
The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...
, but its most striking features are the long rostral and dorsal spines, sometimes augmented by further, lateral spines.
These spines can be many times longer than the body of the larva. Crab prezoea larvae have been found
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 ...
ised in the
stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
contents of the
Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
bony fish
Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...
''
Tharrhias
''Tharrhias'' is an extinct genus of prehistoric bony fish that lived during the Aptian stage of the Early Cretaceous epoch. The type species ''T. araripis'' is named after the Araripe Basin, in which it was found in sediments of the Santana Fo ...
''.
Maxillopoda
Copepoda
Copepod
Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...
s 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.
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.
= 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.
[ ]
Chalimus (plural chalimi) is a stage of development of a copepod parasite of fish, such as the salmon louse (''Lepeophtheirus salmonis'').
''Chalimus'' Burmeister, 1834 is also a synonym for ''
Lepeophtheirus
''Lepeophtheirus'' is a genus of sea louse. The best-known species is ''L. salmonis'', the salmon louse. Other species include '' L. pectoralis'', which uses flatfish as its host, particularly the European flounder, and is also the typ ...
'' Nordmann, 1832.
Facetotecta
The single genus in the
Facetotecta
Facetotecta is a poorly known subclass of thecostracan crustaceans. The adult forms have never been recognised, and the group is known only from its larvae, the "y- nauplius" and "y-cyprid" larvae. They are mostly found in the north Atlantic Ocea ...
, ''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
Hans Jacob Hansen (10 August 1855 – 26 June 1936) was a Danish zoologist, known for his contributions to carcinology (the study of crustacea). He was born in Bellinge and died in Gentofte.
He participated on the first year of the Ingolf expedit ...
, assuming them to be the larvae of
barnacle
A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosiv ...
s.
The adults are presumed to be
parasites
Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...
of other animals.
See also
*
Ichthyoplankton
Ichthyoplankton (from Greek: ἰχθύς, , "fish"; and πλαγκτός, , "drifter") are the eggs and larvae of fish. They are mostly found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epip ...
*
Marine larval ecology Marine larval ecology is the study of the factors influencing dispersing larvae, which many marine invertebrates and fishes have. Marine animals with a larva typically release many larvae into the water column, where the larvae develop before met ...
References
{{Plankton
Crustaceans
Larvae