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Crustaceans (Crustacea ) form a large, diverse
arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...
taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
which includes such animals as
crab Crabs are decapod crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, prawns, woodlice, barnacles, copepods, amphipoda ...

crab
s,
lobster Lobsters are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society ...

lobster
s,
crayfish A man selling dried crayfish at an African market Crayfish are freshwater crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobran ...

crayfish
,
shrimp Shrimp are Decapoda, decapod crustaceans with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata. More narrow definitions may be restricted to Caridea, to smaller species of either group ...
,
krill Krill are small crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...

krill
,
prawns Prawn is a common name for small aquatic crustaceans with an exoskeleton and ten legs (which is a member of the order decapoda), some of which can be eaten. The term "prawn"Mortenson, Philip B (2010''This is not a weasel: a close look at nature ...
,
woodlice A woodlouse (plural woodlice) is a crustacean from the monophyletic suborder Oniscidea within the isopods. This name is descriptive of their being found in old wood. The first woodlice were marine isopods which are presumed to have colonised ...
,
barnacle A barnacle is a type of arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference ...

barnacle
s,
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), ...

copepod
s,
amphipods Amphipoda is an order of malacostraca Malacostraca (New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Ind ...

amphipods
and
mantis shrimp Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda, branching from other members of the class Malacostraca around 340 million years ago. Mantis shrimps typically grow to around in length, while a few c ...

mantis shrimp
. The crustacean group can be treated as a
subphylum In zoological nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted Convention (norm), convention in zoology that rules the formal scientific name, scientific naming of organisms treated as animals. It is als ...
under the
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
Mandibulata Mandibulata, termed "mandibulates", is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ancest ...
; because of recent molecular studies it is now well accepted that the crustacean group is
paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—Monophyly, monophyletic subgroups. The group is said to be paraphyleti ...

paraphyletic
, and comprises all animals in the clade
Pancrustacea Pancrustacea is the clade that comprises all crustaceans and Hexapoda, hexapods. This grouping is contrary to the Atelocerata hypothesis, in which Myriapoda and Hexapoda are sister taxon, sister taxa, and Crustacea are only more distantly related. ...
other than hexapods. Some crustaceans (
Remipedia Remipedia is a class of blind crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, prawns, woodlice, barnacles, copepods, ...
,
Cephalocarida The Cephalocarida are a class in the subphylum Crustacea comprising only 12 benthic species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of b ...
,
Malacostraca Malacostraca (New Latin from Ancient Greek μαλακός ''malakós'' (“soft”) + όστρακον ''óstrakon'' (“shell”)) is the largest of the six class (biology), classes of crustaceans, containing about 40,000 living species, divide ...

Malacostraca
) are more closely related to
insects Insects (from Latin ') are pancrustacean Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, Thorax (ins ...

insects
and the other hexapods than they are to certain other crustaceans. The 67,000 described species range in size from '' Stygotantulus stocki'' at , to the
Japanese spider crab The Japanese spider crab (''Macrocheira kaempferi'') is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is ofte ...

Japanese spider crab
with a leg span of up to and a mass of . Like other
arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...
s, crustaceans have an
exoskeleton An exoskeleton (from Greek έξω, ''éxō'' "outer" and σκελετός, ''skeletós'' "skeleton") is the external skeleton A skeleton is a structural frame that supports an animal Animals (also called Metazoa) are multicellular ...

exoskeleton
, which they
moult In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
to grow. They are distinguished from other groups of arthropods, such as
insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

insect
s,
myriapods Myriapoda (Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycen ...

myriapods
and
chelicerates The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids (including scorpions, spiders, and mites), as well as a number of extin ...
, by the possession of
biramous The arthropod leg is a form of jointed of s, usually used for . Many of the terms used for arthropod leg segments (called podomeres) are of origin, and may be confused with terms for bones: ''coxa'' (meaning , plural ''coxae''), ''trochanter'', '' ...
(two-parted) limbs, and by their
larval forms
larval forms
, such as the nauplius stage of
branchiopod Branchiopoda is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Cladocera, Notostraca and the Devonian '' Lepidocaris''. They are mostly small, freshwater animals that feed on plankton and detritus. Description Members of t ...
s and
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), ...

copepod
s. Most crustaceans are free-living
aquatic animal An aquatic animal is an animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. Al ...
s, but some are
terrestrial Terrestrial refers to things related to land Land is the solid surface of the Earth that is not permanently covered by water. The vast majority of human activity throughout history has occurred in land areas that support agriculture A ...
(e.g.
woodlice A woodlouse (plural woodlice) is a crustacean from the monophyletic suborder Oniscidea within the isopods. This name is descriptive of their being found in old wood. The first woodlice were marine isopods which are presumed to have colonised ...
), some are
parasitic Parasitism is a Symbiosis, symbiotic biological interactions, 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 (biology), ad ...

parasitic
(e.g.
Rhizocephala Rhizocephala are derived barnacle A barnacle is a type of arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form ...
, fish lice, tongue worms) and some are sessile (e.g.
barnacle A barnacle is a type of arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference ...

barnacle
s). The group has an extensive
fossil record A fossil (from Classical Latin: , literally 'obtained by digging') is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, Seashell, shells, exoskeletons, stone imprints of a ...
, reaching back to the
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These peri ...
. More than 7.9 million tons of crustaceans per year are produced by fishery or farming for human consumption, most of it being shrimp and prawns.
Krill Krill are small crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...

Krill
and
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), ...

copepod
s are not as widely fished, but may be the animals with the greatest
biomass Biomass is plant or animal material used as fuel to produce electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position ...
on the planet, and form a vital part of the food chain. The scientific study of crustaceans is known as
carcinology Carcinology is a branch of zoology Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the anatomy, structure, embryolog ...
(alternatively, ''malacostracology'', ''crustaceology'' or ''crustalogy''), and a
scientist A scientist is a person who conducts scientific research The scientific method is an Empirical evidence, empirical method of acquiring knowledge that has characterized the development of science since at least the 17th century. It involves ...

scientist
who works in carcinology is a
carcinologist A carcinologist is a scientist who studies crustaceans or is otherwise involved in carcinology (the science of crustaceans). References

{{Reflist, 24em Carcinologists, . Lists of zoologists, Carcinologists ...
.


Structure

The body of a crustacean is composed of segments, which are grouped into three regions: the ''cephalon'' or
head Head Sport GmbH is an American-Austrian manufacturing company Manufacturing is the creation or production Production may be: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in th ...

head
, the ''pereon'' or
thorax The thorax or chest is a part of the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bioc ...

thorax
, and the ''pleon'' or
abdomen The abdomen (colloquially called the belly, tummy, midriff 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 Trunk (anatomy) ...

abdomen
. The head and thorax may be fused together to form a
cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...
, which may be covered by a single large
carapace A carapace is a Dorsum (biology), 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 tor ...
. The crustacean body is protected by the hard
exoskeleton An exoskeleton (from Greek έξω, ''éxō'' "outer" and σκελετός, ''skeletós'' "skeleton") is the external skeleton A skeleton is a structural frame that supports an animal Animals (also called Metazoa) are multicellular ...

exoskeleton
, which must be moulted for the animal to grow. The shell around each somite can be divided into a dorsal
tergum A tergum (Latin for "the back"; plural terga, associated adjective tergal) is the dorsal ('upper') portion of an arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented bo ...
, ventral
sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, human lung, lungs, and major blood vessels from in ...
and a lateral pleuron. Various parts of the exoskeleton may be fused together. Each
somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm Paraxial mesoderm, also known as presomitic or somitic mesoderm is the area of mesoderm In all bilaterian animals, the mesoderm is one o ...

somite
, or body segment can bear a pair of
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a ...
s: on the segments of the head, these include two pairs of
antennae Antenna (pl. antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two coll ...
, the
mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of li ...
s and
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The tw ...
e; the thoracic segments bear
legs A leg is a weight-bearingIn orthopedics Orthopedic surgery or orthopedics, is the branch of surgery concerned with conditions involving the musculoskeletal system. Orthopedic surgeons use both surgical and nonsurgical means to treat muscul ...
, which may be specialised as
pereiopod The decapod crustacea Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthr ...
s (walking legs) and
maxilliped An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a b ...
s (feeding legs). The abdomen bears
pleopod The decapod crustacea Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arth ...
s, and ends in a
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 (biology), segment of the arthropod body, or an additional division that is not a true se ...
, which bears the
anus The anus (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

anus
, and is often flanked by uropods to form a tail fan. The number and variety of
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a ...
s in different crustaceans may be partly responsible for the group's success. Crustacean
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a ...
s are typically
biramous The arthropod leg is a form of jointed of s, usually used for . Many of the terms used for arthropod leg segments (called podomeres) are of origin, and may be confused with terms for bones: ''coxa'' (meaning , plural ''coxae''), ''trochanter'', '' ...
, meaning they are divided into two parts; this includes the second pair of antennae, but not the first, which is usually
uniramous The arthropod leg is a form of jointed appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism () is any organic, life, living system that funct ...
, the exception being in the Class Malacostraca where the antennules may be generally biramous or even triramous. It is unclear whether the biramous condition is a derived state which evolved in crustaceans, or whether the second branch of the limb has been lost in all other groups.
Trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the of the ( ...

Trilobite
s, for instance, also possessed biramous appendages. The main body cavity is an
open circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an Biological system, organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, ...

open circulatory system
, where blood is pumped into the
haemocoel The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrient A nutrient ...
by a
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
located near the dorsum. Malacostraca have haemocyanin as the oxygen-carrying pigment, while copepods, ostracods, barnacles and branchiopods have
haemoglobin Hemoglobin or haemoglobin (spelling differences) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood ce ...

haemoglobin
s. The alimentary canal consists of a straight tube that often has a gizzard-like "gastric mill" for grinding food and a pair of digestive glands that absorb food; this structure goes in a spiral format. Structures that function as kidneys are located near the antennae. A brain exists in the form of ganglia close to the antennae, and a collection of major ganglia is found below the gut. In many
decapods The Decapoda or decapods (literally "ten-footed") are an order of crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, p ...
, the first (and sometimes the second) pair of pleopods are specialised in the male for sperm transfer. Many terrestrial crustaceans (such as the
Christmas Island red crab The Christmas Island red crab (''Gecarcoidea natalis'') is a species of terrestrial crab, land crab that is endemism, endemic to Christmas Island and Cocos (Keeling) Islands in the Indian Ocean. Although restricted to a relatively small area, an ...

Christmas Island red crab
) mate seasonally and return to the sea to release the eggs. Others, such as
woodlice A woodlouse (plural woodlice) is a crustacean from the monophyletic suborder Oniscidea within the isopods. This name is descriptive of their being found in old wood. The first woodlice were marine isopods which are presumed to have colonised ...
, lay their eggs on land, albeit in damp conditions. In most decapods, the females retain the eggs until they hatch into free-swimming larvae.


Ecology

Most crustaceans are aquatic, living in either marine or
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in ...

freshwater
environments, but a few groups have
adapted In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process that fits organisms to their environment, enhancing their Fitness (biology), evolutionary fitness. Secondly, it is a state reached by the popula ...

adapted
to life on land, such as
terrestrial crab A number of lineages of crab Crabs are Decapoda, decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen#Other animals, abdomen) ( el, :wikt:βραχύς, βραχύς , translit=brachys = ...
s, terrestrial hermit crabs, and
woodlice A woodlouse (plural woodlice) is a crustacean from the monophyletic suborder Oniscidea within the isopods. This name is descriptive of their being found in old wood. The first woodlice were marine isopods which are presumed to have colonised ...
. Marine crustaceans are as ubiquitous in the oceans as insects are on land. Most crustaceans are also
motile Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with Sessility (motility), sessility, the ...

motile
, moving about independently, although a few taxonomic units are
parasitic Parasitism is a Symbiosis, symbiotic biological interactions, 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 (biology), ad ...
and live attached to their hosts (including sea lice, ,
whale lice A whale louse is a commensal crustacean of the family Cyamidae. Despite the name, it is not a true louse (which are insect Insects or Insecta (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic ...
, tongue worms, and ''
Cymothoa exigua ''Cymothoa exigua'', or the tongue-eating louse, is a parasitic Parasitism is a Symbiosis, symbiotic biological interactions, relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (b ...
'', all of which may be referred to as "crustacean lice"), and adult barnacles live a sessile life – they are attached headfirst to the substrate and cannot move independently. Some branchiurans are able to withstand rapid changes of
salinity Salinity () is the saltiness or amount of salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific ...

salinity
and will also switch hosts from marine to non-marine species.
Krill Krill are small crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...

Krill
are the bottom layer and the most important part of the food chain in
Antarctic The Antarctic (US English or , UK English or and or ) is a around 's , opposite the region around the . The Antarctic comprises the continent of , the and other located on the or south of the . The Antarctic region includes the , wa ...

Antarctic
animal communities. Some crustaceans are significant invasive species, such as the Chinese mitten crab, ''
Eriocheir sinensis The Chinese mitten crab ('; ,  "big sluice crab"), also known as the Shanghai hairy crab (, pinyin, p ''Shànghǎi máoxiè''), is a medium-sized burrowing crab that is named for its furry claws, which resemble mittens. It is native to ...

Eriocheir sinensis
'', and the Asian shore crab, ''''.


Life cycle


Mating system

Most crustaceans have separate sexes, and reproduce sexually. In fact, a recent study explains how the male crustaceans,T. Californicus decide which females to mate with by dietary differences, preferring when the females are algae-fed instead of yeast-fed. A small number are
hermaphrodite In reproductive biology Reproductive biology includes both sexual and asexual reproduction. Reproductive biology includes a wide number of fields: * Reproductive systems * Endocrinology Endocrinology (from '' endocrine'' + '' -ology'') is a ...

hermaphrodite
s, including
barnacle A barnacle is a type of arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference ...

barnacle
s,
remipede 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 f ...
s, and
Cephalocarida The Cephalocarida are a class in the subphylum Crustacea comprising only 12 benthic species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of b ...
. Some may even change sex during the course of their life.
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 Asexual reproduction is a typ ...
is also widespread among crustaceans, where viable eggs are produced by a female without needing fertilisation by a male. This occurs in many
branchiopod Branchiopoda is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Cladocera, Notostraca and the Devonian '' Lepidocaris''. They are mostly small, freshwater animals that feed on plankton and detritus. Description Members of t ...
s, some
ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant taxon, extant) have been identified, grouped into several o ...

ostracod
s, some
isopod Isopoda is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, an ...

isopod
s, and certain "higher" crustaceans, such as the '' Marmorkrebs'' crayfish.


Eggs

In many groups of crustaceans, the fertilised eggs are simply released into the
water column A water column is a concept Concepts are defined as abstract ideas A mental representation (or cognitive representation), in philosophy of mind Philosophy of mind is a branch of philosophy that studies the ontology and nature of the mind ...
, while others have developed a number of mechanisms for holding on to the eggs until they are ready to hatch. Most
decapods The Decapoda or decapods (literally "ten-footed") are an order of crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, p ...
carry the eggs attached to the
pleopod The decapod crustacea Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arth ...
s, while peracarids,
notostraca The order Notostraca, containing the single family Triopsidae, is a group of crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation ...
ns,
anostraca Anostraca is one of the four orders Orders is a surname In some cultures, a surname, family name, or last name is the portion of one's personal name 300px, First/given, middle and last/family/surname with John Fitzgerald Kennedy as ex ...
ns, and many
isopod Isopoda is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, an ...

isopod
s form a brood pouch from the
carapace A carapace is a Dorsum (biology), 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 tor ...
and thoracic limbs. Female Branchiura do not carry eggs in external ovisacs but attach them in rows to rocks and other objects. Most
leptostraca Leptostraca (from the Greek language, Greek words for ''thin'' and ''shell'') is an order (biology), order of small, marine crustaceans. Its members, including the well-studied ''Nebalia'', occur throughout the world's oceans and are usually consi ...
ns and
krill Krill are small crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...

krill
carry the eggs between their thoracic limbs; some
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), ...

copepod
s carry their eggs in special thin-walled sacs, while others have them attached together in long, tangled strings.


Larvae

Crustaceans exhibit a number of larval forms, of which the earliest and most characteristic is the nauplius. This has three pairs of
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a ...
s, all emerging from the young animal's head, and a single naupliar eye. In most groups, there are further larval stages, including the
zoea 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 Biology is the natural science that studies life and l ...
(pl. zoeæ or zoeas). This name was given to it when naturalists believed it to be a separate species. It follows the nauplius stage and precedes the post-larva. Zoea larvae swim with their thoracic
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a ...
s, as opposed to nauplii, which use cephalic appendages, and megalopa, which use abdominal appendages for swimming. It often has spikes on its
carapace A carapace is a Dorsum (biology), 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 tor ...
, which may assist these small organisms in maintaining directional swimming. In many
decapods The Decapoda or decapods (literally "ten-footed") are an order of crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, p ...
, due to their accelerated development, the zoea is the first larval stage. In some cases, the zoea stage is followed by the mysis stage, and in others, by the megalopa stage, depending on the crustacean group involved.


Classification and phylogeny

The name "crustacean" dates from the earliest works to describe the animals, including those of
Pierre Belon Pierre Belon (1517–1564) was a French traveler, naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organ ...
and
Guillaume Rondelet Guillaume Rondelet (27 September 150730 July 1566), also known as Rondeletus/Rondeletius, was Regius professor of medicine at the University of Montpellier in southern France and Chancellor of the University between 1556 and his death in 1566. He ...
, but the name was not used by some later authors, including
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement Ennoblement is the conferring of nobility—the induction of an individual into the noble social class, class. Currently only a few kingdoms still grant nob ...

Carl Linnaeus
, who included crustaceans among the " Aptera" in his '. The earliest nomenclaturally valid work to use the name "Crustacea" was
Morten Thrane Brünnich Morten Thrane Brünnich (30 September 1737 – 19 September 1827) was a Danish zoologist Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the ani ...
's ' in 1772, although he also included
chelicerates The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids (including scorpions, spiders, and mites), as well as a number of extin ...
in the group. The subphylum Crustacea comprises almost 67,000 described
species In biology, a species is the basic unit of biological classification, 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 individu ...

species
, which is thought to be just to of the total number as most species remain as yet
undiscovered ''Undiscovered'' is a 2005 film directed by Meiert Avis. The plot is about a group of aspiring entertainers who intend to establish their careers in Los Angeles, California, Los Angeles. Released on August 26, 2005, the film received a largely neg ...
. Although most crustaceans are small, their morphology varies greatly and includes both the largest arthropod in the world – the
Japanese spider crab The Japanese spider crab (''Macrocheira kaempferi'') is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is ofte ...

Japanese spider crab
with a leg span of – and the smallest, the 100-
micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental orga ...
-long (0.004 in) '' Stygotantulus stocki''. Despite their diversity of form, crustaceans are united by the special
larva A larva (plural larvae ) is a distinct juvenile form many animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that f ...
l form known as the nauplius. The exact relationships of the Crustacea to other taxa are not completely settled . Studies based on morphology led to the
Pancrustacea Pancrustacea is the clade that comprises all crustaceans and Hexapoda, hexapods. This grouping is contrary to the Atelocerata hypothesis, in which Myriapoda and Hexapoda are sister taxon, sister taxa, and Crustacea are only more distantly related. ...
hypothesis, in which Crustacea and
Hexapoda The subphylum Hexapoda (from Greek language, Greek for 'six legs') comprises most species of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Springtail, Collembola, Protura, and Diplura (all of the ...
(
insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

insect
s and allies) are
sister group In phylogenetics, a sister group or sister taxon comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and taxon B are sister groups to eac ...
s. More recent studies using
DNA sequence DNA sequencing is the process of determining the nucleic acid sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic ...

DNA sequence
s suggest that Crustacea is
paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—Monophyly, monophyletic subgroups. The group is said to be paraphyleti ...

paraphyletic
, with the hexapods nested within a larger Pancrustacea
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
. Although the classification of crustaceans has been quite variable, the system used by Martin and Davis largely supersedes earlier works.
Mystacocarida Mystacocarida is a subclass of crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointe ...

Mystacocarida
and
Branchiura Branchiura is a group of crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed ap ...

Branchiura
, here treated as part of
Maxillopoda Maxillopoda is a diverse class of crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jo ...
, are sometimes treated as their own classes. Six classes are usually recognised: The following cladogram shows the updated relationships between the different extant groups of the paraphyletic Crustacea in relation to the class
Hexapoda The subphylum Hexapoda (from Greek language, Greek for 'six legs') comprises most species of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Springtail, Collembola, Protura, and Diplura (all of the ...
.


Fossil record

Crustaceans have a rich and extensive
fossil record A fossil (from Classical Latin: , literally 'obtained by digging') is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, Seashell, shells, exoskeletons, stone imprints of a ...
, which begins with animals such as '''' and ''Perspicaris'' from the Middle Cambrian age Burgess Shale. Most of the major groups of crustaceans appear in the fossil record before the end of the Cambrian, namely the Branchiopoda,
Maxillopoda Maxillopoda is a diverse class of crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jo ...
(including
barnacle A barnacle is a type of arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference ...

barnacle
s and tongue worms) and
Malacostraca Malacostraca (New Latin from Ancient Greek μαλακός ''malakós'' (“soft”) + όστρακον ''óstrakon'' (“shell”)) is the largest of the six class (biology), classes of crustaceans, containing about 40,000 living species, divide ...

Malacostraca
; there is some debate as to whether or not Cambrian animals assigned to Ostracoda are truly
ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant taxon, extant) have been identified, grouped into several o ...

ostracod
s, which would otherwise start in the Ordovician. The only classes to appear later are the
Cephalocarida The Cephalocarida are a class in the subphylum Crustacea comprising only 12 benthic species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of b ...
, which have no fossil record, and the
Remipedia Remipedia is a class of blind crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, prawns, woodlice, barnacles, copepods, ...
, which were first described from the fossil ''Tesnusocaris, Tesnusocaris goldichi'', but do not appear until the Carboniferous. Most of the early crustaceans are rare, but fossil crustaceans become abundant from the Carboniferous period onwards. Within the Malacostraca, no fossils are known for
krill Krill are small crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...

krill
, while both Hoplocarida and Phyllopoda contain important groups that are now extinct as well as extant members (Hoplocarida:
mantis shrimp Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda, branching from other members of the class Malacostraca around 340 million years ago. Mantis shrimps typically grow to around in length, while a few c ...

mantis shrimp
are extant, while Aeschronectida are extinct; Phyllopoda: Canadaspidida are extinct, while Leptostraca are extant). Cumacea and Isopoda are both known from the Carboniferous, as are the first true mantis shrimp. In the Decapoda,
prawns Prawn is a common name for small aquatic crustaceans with an exoskeleton and ten legs (which is a member of the order decapoda), some of which can be eaten. The term "prawn"Mortenson, Philip B (2010''This is not a weasel: a close look at nature ...
and Polychelida, polychelids appear in the Triassic, and
shrimp Shrimp are Decapoda, decapod crustaceans with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata. More narrow definitions may be restricted to Caridea, to smaller species of either group ...
and
crab Crabs are decapod crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, prawns, woodlice, barnacles, copepods, amphipoda ...

crab
s appear in the Jurassic;. The fossil burrow ''Ophiomorpha'' is attributed to ghost shrimps, whereas the fossil burrow ''Camborygma'' is attributed to crayfishes. The Permian–Triassic deposits of Nurra preserve the oldest (Permian: Roadian) fluvial burrows ascribed to ghost shrimps (Decapoda: Axiidea, Gebiidea) and crayfishes (Decapoda: Astacidea, Parastacidea), respectively. However, the great radiation of crustaceans occurred in the Cretaceous, particularly in crabs, and may have been driven by the adaptive radiation of their main predators, bony fish. The first true
lobster Lobsters are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society ...

lobster
s also appear in the Cretaceous.


Consumption by humans

Many crustaceans are consumed by humans, and nearly 10,700,000 tons were produced in 2007; the vast majority of this output is of Decapoda, decapod crustaceans:
crab Crabs are decapod crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, Caridea, shrimp, krill, Dendrobranchiata, prawns, woodlice, barnacles, copepods, amphipoda ...

crab
s,
lobster Lobsters are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society ...

lobster
s, shrimp, crawfish, and
prawns Prawn is a common name for small aquatic crustaceans with an exoskeleton and ten legs (which is a member of the order decapoda), some of which can be eaten. The term "prawn"Mortenson, Philip B (2010''This is not a weasel: a close look at nature ...
. Over 60% by weight of all crustaceans caught for consumption are shrimp and prawns, and nearly 80% is produced in Asia, with China alone producing nearly half the world's total. Non-decapod crustaceans are not widely consumed, with only 118,000 tons of
krill Krill are small crustacean Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ...

krill
being caught, despite krill having one of the greatest Biomass (ecology), biomasses on the planet.


See also

* Pain in crustaceans


References


Sources

* Powers, M., Hill, G., Weaver, R., & Goymann, W. (2020). An experimental test of mate choice for red carotenoid coloration in the marine copepod Tigriopus californicus. Ethology., 126(3), 344–352. https://doi.org/10.1111/eth.12976


External links

*
Crustacea.net, an online resource on the biology of crustaceansCrustacea
Natural History Museum of Los Angeles County
Crustacea
Tree of Life Web Project
The Crustacean SocietyNatural History Collections: Crustacea
University of Edinburgh
Crustaceans (Crustacea) on the shore of SingaporeCrustacea(crabs, lobsters, shrimps, prawns, barnacles)
Biodiversity Explorer {{Good article Crustaceans, Cambrian Series 2 first appearances Extant Cambrian first appearances Paraphyletic groups