Cladocera
Encyclopedia
Cladocera is an order
of small crustacean
s commonly called water fleas. Around 620 species have been recognised so far, with many more undescribed. They are ubiquitous in inland aquatic habitats, but rare in the oceans. Most are 0.2 millimetre long, with a down-turned head, and a carapace covering the apparently unsegmented thorax and abdomen. There is a single median compound eye. Most species show cyclical parthenogenesis
, where asexual reproduction
is occasionally supplemented by sexual reproduction
, which produces resting eggs that allow the species to survive harsh conditions and disperse to distant habitats.
, which can be up to 18 mm (0.708661417322835 in) long. The body is not obviously segmented and bears a folded carapace
which covers the thorax
and abdomen
.
The head is angled downwards, and may be separated from the rest of the body by a "cervical sinus" or notch. It bears a single black compound eye, located on the animal's midline, in all but two genera, and there is often a single ocellus
. The head also bears two pairs of antennae
– the first antennae are small unsegmented appendages, while the second antennae are large, segmented and branched, with powerful muscles. The first antennae bear olfactory seta
e, while the second are used for swimming by most species. The pattern of setae on the second antennae is useful for identification; Daphnia. The part of the head which projects in front of the first antennae is known as the rostrum
or "beak".
The mouthparts are small, and consist of an unpaired labrum, a pair of mandibles, a pair of maxillae, and an unpaired labium. They are used to eat "organic detritus of all kinds" and bacteria
.
The thorax bears five or six pairs of lobed, leaf-like appendages, each with numerous hairs or setae. Carbon dioxide
is lost, and oxygen
taken up, through the body surface.
of cladocerans is dominated by asexual reproduction
, with occasional periods of sexual reproduction
; this is known as cyclical parthenogenesis. The system evolved in the Permian
, at the same time that the Cladocera arose. When conditions are favourable, reproduction occurs by parthenogenesis
for several generations, producing only female clones
. As the conditions deteriorate, males are produced, and sexual reproduction occurs. This results in the production of long-lasting dormant eggs
. These ephippial eggs can be transported over land by wind, and hatch when they reach favourable conditions, allowing many species to have very wide – even cosmopolitan
– distributions
.
and other inland water bodies, with only eight species being truly neritic
(oceanic). The marine species are all in the family Podonidae, except for the genus Penilia.
, and forms a monophyletic group
, which is currently divided into four suborders. Around 620 species
have been described, but many more species remain undescribed. The genus Daphnia
alone contains around 150 species.
The following families are recognised:
Order Cladocera Latreille, 1829
from the Ancient Greek
(, "branch") and (, "horn").
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of small crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s commonly called water fleas. Around 620 species have been recognised so far, with many more undescribed. They are ubiquitous in inland aquatic habitats, but rare in the oceans. Most are 0.2 millimetre long, with a down-turned head, and a carapace covering the apparently unsegmented thorax and abdomen. There is a single median compound eye. Most species show cyclical parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
, where asexual reproduction
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
is occasionally supplemented by sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
, which produces resting eggs that allow the species to survive harsh conditions and disperse to distant habitats.
Description
They are mostly 0.2–6 mm (0.0078740157480315–0.236220472440945 ) long, with the exception of LeptodoraLeptodora
Leptodora is a genus containing two species of large, nearly transparent predatory water fleas. They grow up to long, with two large antennae used for swimming and a single compound eye. The legs are used to catch other copepods that it comes into contact with by chance...
, which can be up to 18 mm (0.708661417322835 in) long. The body is not obviously segmented and bears a folded carapace
Carapace
A carapace is a dorsal 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 underside is called the plastron.-Crustaceans:In crustaceans, the...
which covers the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
and abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
.
The head is angled downwards, and may be separated from the rest of the body by a "cervical sinus" or notch. It bears a single black compound eye, located on the animal's midline, in all but two genera, and there is often a single ocellus
Ocellus
A simple eye refers to a type of eye design or optical arrangement that contains a single lens which detect light. A "simple eye" is so-called in distinction from a multi-lensed "compound eye", and is not necessarily at all simple in the usual sense of the word...
. The head also bears two pairs of antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
– the first antennae are small unsegmented appendages, while the second antennae are large, segmented and branched, with powerful muscles. The first antennae bear olfactory seta
Seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....
e, while the second are used for swimming by most species. The pattern of setae on the second antennae is useful for identification; Daphnia. The part of the head which projects in front of the first antennae is known as the rostrum
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
or "beak".
The mouthparts are small, and consist of an unpaired labrum, a pair of mandibles, a pair of maxillae, and an unpaired labium. They are used to eat "organic detritus of all kinds" and bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
.
The thorax bears five or six pairs of lobed, leaf-like appendages, each with numerous hairs or setae. Carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
is lost, and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
taken up, through the body surface.
Life cycle
With the exception of a few purely asexual species, the life cycleBiological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
of cladocerans is dominated by asexual reproduction
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
, with occasional periods of sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
; this is known as cyclical parthenogenesis. The system evolved in the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
, at the same time that the Cladocera arose. When conditions are favourable, reproduction occurs by parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
for several generations, producing only female clones
Cloning
Cloning in biology is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or...
. As the conditions deteriorate, males are produced, and sexual reproduction occurs. This results in the production of long-lasting dormant eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
. These ephippial eggs can be transported over land by wind, and hatch when they reach favourable conditions, allowing many species to have very wide – even cosmopolitan
Cosmopolitan distribution
In biogeography, a taxon is said to have a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans. Other examples include humans, the lichen...
– distributions
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
.
Ecology
Most cladoceran species live in fresh waterFresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
and other inland water bodies, with only eight species being truly neritic
Neritic zone
The neritic zone, also called coastal waters, the coastal ocean or the sublittoral zone, is the part of the ocean extending from the low tide mark to the edge of the continental shelf, with a relatively shallow depth extending to about 200 meters...
(oceanic). The marine species are all in the family Podonidae, except for the genus Penilia.
Taxonomy
The order Cladocera is included in the class BranchiopodaBranchiopoda
Branchiopoda is a class of crustaceans. It is the sister group to the remaining crustaceans, and comprises fairy shrimp, clam shrimp, Cladocera, Notostraca and the Devonian Lepidocaris...
, and forms a monophyletic group
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
, which is currently divided into four suborders. Around 620 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
have been described, but many more species remain undescribed. The genus Daphnia
Daphnia
Daphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...
alone contains around 150 species.
The following families are recognised:
Order Cladocera Latreille, 1829
- Suborder Ctenopoda Sars, 1865
- Holopediidae Sars, 1865
- Sididae Baird, 1850
- Suborder AnomopodaAnomopodaAnomopoda is a suborder of the order Cladocera. These crustaceans, a type of water flea, are members of the Class Branchiopoda. The Anomopoda typically have five pairs of thoracic limbs, but sometimes have six pairs. The head of the Anomopoda lacks a clear separation from the trunk and the...
Stebbing, 1902- Bosminidae Baird, 1845
- Chydoridae Stebbing, 1902
- DaphniidaeDaphniidaeDaphniidae is a family in the order Cladocera . Species within this family occur in several places within Africa including Lake Chad in northwest Africa and in the Makgadikgadi Pans in Botswana...
Straus, 1820 - Gondwanotrichidae Van Damme et al., 2007
- Macrotrichidae Norman & Brady, 1867
- Suborder OnychopodaOnychopodaOnychopoda are a specialised suborder of branchiopod crustaceans, belonging to the order Cladocera.The suborder Onychopoda is "one of the most morphologically distinctive groups of cladocerans". They have only four pairs of legs, compared to five or six pairs in Ctenopoda and Anomopoda...
Sars, 1865- Cercopagididae Mordukhai-Boltovskoi, 1968
- Podonidae Mordukhai-Boltovskoi, 1968
- Polyphemidae Baird, 1845
- Suborder HaplopodaLeptodoraLeptodora is a genus containing two species of large, nearly transparent predatory water fleas. They grow up to long, with two large antennae used for swimming and a single compound eye. The legs are used to catch other copepods that it comes into contact with by chance...
Sars, 1865- LeptodoridaeLeptodoraLeptodora is a genus containing two species of large, nearly transparent predatory water fleas. They grow up to long, with two large antennae used for swimming and a single compound eye. The legs are used to catch other copepods that it comes into contact with by chance...
Lilljeborg, 1900
- Leptodoridae
Etymology
The word "Cladocera" derives via New LatinNew Latin
The term New Latin, or Neo-Latin, is used to describe the Latin language used in original works created between c. 1500 and c. 1900. Among other uses, Latin during this period was employed in scholarly and scientific publications...
from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
(, "branch") and (, "horn").
External links
- Waterflea.org – a community resource for cladoceran biology
- Cladocera – Guide to the Marine Zooplankton of South Eastern Australia