Branchiopoda
Encyclopedia
Branchiopoda is a class
of crustacean
s. It is the sister group to the remaining crustaceans, and comprises fairy shrimp, clam shrimp
, Cladocera
, Notostraca
and the Devonian Lepidocaris
. They are mostly small, freshwater animals that feed on plankton and detritus, with the exception of the Cladocera, many of which are marine.
s on many of the animals' appendage
s, including some of the mouthparts. This is also responsible for the name of the group (from the , gills, akin to , windpipe; , foot). They generally possess compound eyes and a carapace
, which may be a shell of two valves enclosing the trunk (as in most Cladocera), broad and shallow (as in the Notostraca), or entirely absent (as in the Anostraca). In the groups where the carapace prevents the use of the trunk limbs for swimming (Cladocera, clam shrimp and the extinct Lipostraca), the antennae
are used for locomotion, as they are in the nauplius. Male fairy shrimp have an enlarged pair of antennae with which they grasp the female during mating, while the bottom-feeding
Notostraca, the antennae are reduced to vestiges. The trunk limbs are beaten in a metachronal rhythm
, causing a flow of water along the midline of the animal, from which it derives oxygen
, food
and, in the case of the Anostraca and Notostraca, movement.
ns are marine; all the other groups are found in continental waters fresh water
, including temporary pools
and salt lakes. Most branchiopodans eat floating detritus
or plankton
, which they take using the seta
e on their appendages.
in 1817, initially at the rank
of order
.
. They live in vernal pool
s and hypersaline lake
s across the world, including pools in desert
s, in ice-covered mountain lakes and in Antarctica. They swim "upside-down" and feed by filtering
organic particles from the water or by scraping algae
from surfaces. They are an important food for many birds and fish, and are cultured and harvested for use as fish food. There are 300 species spread across 8 families
.
, which is the most abundant animal in the Rhynie chert
desposits. It resembles modern Anostraca, to which it is probably closely related, although its relationships to other orders remain unclear. The body is 3 mm (0.118110236220472 in) long, with 23 body segments and 19 pairs of appendage
s, but no carapace
. It occurred chiefly among charophytes, probably in alkaline temporary pools
.
comprises the single family Triopsidae, containing the tadpole shrimp or shield shrimp. The two genera, Triops
and Lepidurus
, are considered living fossil
s, having not changed significantly in outward form since the Triassic
. They have a broad, flat carapace, which conceals the head and bears a single pair of compound eyes. The abdomen is long, appears to be segmented and bears numerous pairs of flattened legs. The telson
is flanked by a pair of long, thin caudal rami. Phenotypic plasticity
within taxa makes species-level identification difficult, and is further compounded by variation in the mode of reproduction. Notostracans are the largest branchiopodans and are omnivore
s living on the bottom of temporary pools and shallow lakes.
. The three groups are not believed to form a clade
. They have 10–32 trunk segments, decreasing in size from front to back, and each bears a pair of legs
which also carry gill
s. A strong muscle can close the two halves of the shell together.
Cladocera
is an order
of small crustacean
s commonly called water fleas. Around 620 species have been recognised so far, with may more undescribed. They are ubiquitous in inland aquatic habitats, but rare in the oceans. Most are 0.2–6 mm (0.0078740157480315–0.236220472440945 ) 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.
, with the Anostraca having been the first group to branch off
. It is thought that the group evolved in the seas, but was forced into temporary pools
and hypersaline lake
s by the evolution of bony fishes
.
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
of 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. It is the sister group to the remaining crustaceans, and comprises fairy shrimp, clam shrimp
Clam shrimp
Clam shrimp are a taxon of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant, and known from the fossil record, from at least the Devonian period and perhaps before...
, Cladocera
Cladocera
Cladocera is an order of small crustaceans 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 long, with a down-turned head, and a carapace covering the apparently...
, Notostraca
Notostraca
The order Notostraca comprises the single family Triopsidae, containing the tadpole shrimp or shield shrimp. The two genera, Triops and Lepidurus, are considered living fossils, having not changed significantly in outward form since the Triassic. They have a broad, flat carapace, which conceals the...
and the Devonian Lepidocaris
Lepidocaris
Lepidocaris rhyniensis is an extinct species of crustacean. It is the only species known from the order Lipostraca, and is the only abundant animal in the Rhynie chert desposits. It resembles modern Anostraca, to which it is probably closely related, although its relationships to other orders...
. They are mostly small, freshwater animals that feed on plankton and detritus, with the exception of the Cladocera, many of which are marine.
Description
Members of the Branchiopoda are unified by the presence of gillGill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s on many of the animals' appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...
s, including some of the mouthparts. This is also responsible for the name of the group (from the , gills, akin to , windpipe; , foot). They generally possess compound eyes and a 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 may be a shell of two valves enclosing the trunk (as in most Cladocera), broad and shallow (as in the Notostraca), or entirely absent (as in the Anostraca). In the groups where the carapace prevents the use of the trunk limbs for swimming (Cladocera, clam shrimp and the extinct Lipostraca), the 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....
are used for locomotion, as they are in the nauplius. Male fairy shrimp have an enlarged pair of antennae with which they grasp the female during mating, while the bottom-feeding
Bottom feeder
Demersal fish live on or near the bottom of the sea or lakes. They occupy the sea floors and lake beds, which usually consist of mud, sand, gravel or rocks. In coastal waters they are found on or near the continental shelf, and in deep waters they are found on or near the continental slope or along...
Notostraca, the antennae are reduced to vestiges. The trunk limbs are beaten in a metachronal rhythm
Metachronal rhythm
A metachronal rhythm or metachronal wave refers to wavy movements produced by the sequential action of structures such as cilia, segments of worms or legs. These movements produce the appearance of a travelling wave. A Mexican wave is a large scale example of a metachronal wave...
, causing a flow of water along the midline of the animal, from which it derives 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...
, food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
and, in the case of the Anostraca and Notostraca, movement.
Ecology
Among the branchiopods, only some cladoceraCladocera
Cladocera is an order of small crustaceans 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 long, with a down-turned head, and a carapace covering the apparently...
ns are marine; all the other groups are found in continental waters fresh water
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
, including temporary pools
Vernal pool
Vernal pools, also called vernal ponds or ephemeral pools, are temporary pools of water. They are usually devoid of fish, and thus allow the safe development of natal amphibian and insect species...
and salt lakes. Most branchiopodans eat floating detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
or plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
, which they take using the 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 on their appendages.
Taxonomy
In early taxonomic treatments, the current members of the Branchiopoda were all placed in a single genus, Monoculus. The taxon Branchiopoda was erected by Pierre André LatreillePierre André Latreille
Pierre André Latreille was a French zoologist, specialising in arthropods. Having trained as a Roman Catholic priest before the French Revolution, Latreille was imprisoned, and only regained his freedom after recognising a rare species he found in the prison, Necrobia ruficollis...
in 1817, initially at the rank
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
of order
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...
.
Anostraca
The fairy shrimp of the order Anostraca are usually 6 millimetre long (exceptionally up to 170 mm or 6.7 in). Most species have 20 body segments, bearing 11 pairs of leaf-like phyllopodia (swimming legs), and the body lacks a carapaceCarapace
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...
. They live in vernal pool
Vernal pool
Vernal pools, also called vernal ponds or ephemeral pools, are temporary pools of water. They are usually devoid of fish, and thus allow the safe development of natal amphibian and insect species...
s and hypersaline lake
Hypersaline lake
A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride or other mineral salts, with saline levels surpassing that of ocean water . Specific microbial and crustacean species thrive in these high salinity environments that are otherwise...
s across the world, including pools in desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
s, in ice-covered mountain lakes and in Antarctica. They swim "upside-down" and feed by filtering
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
organic particles from the water or by scraping algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
from surfaces. They are an important food for many birds and fish, and are cultured and harvested for use as fish food. There are 300 species spread across 8 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
.
Lipostraca
Lipostraca cotains a single species, Lepidocaris rhyniensisLepidocaris
Lepidocaris rhyniensis is an extinct species of crustacean. It is the only species known from the order Lipostraca, and is the only abundant animal in the Rhynie chert desposits. It resembles modern Anostraca, to which it is probably closely related, although its relationships to other orders...
, which is the most abundant animal in the Rhynie chert
Rhynie chert
The Rhynie chert is an Early Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness . It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is located some 700 m away...
desposits. It resembles modern Anostraca, to which it is probably closely related, although its relationships to other orders remain unclear. The body is 3 mm (0.118110236220472 in) long, with 23 body segments and 19 pairs of appendage
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...
s, but no 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...
. It occurred chiefly among charophytes, probably in alkaline temporary pools
Vernal pool
Vernal pools, also called vernal ponds or ephemeral pools, are temporary pools of water. They are usually devoid of fish, and thus allow the safe development of natal amphibian and insect species...
.
Notostraca
The order NotostracaNotostraca
The order Notostraca comprises the single family Triopsidae, containing the tadpole shrimp or shield shrimp. The two genera, Triops and Lepidurus, are considered living fossils, having not changed significantly in outward form since the Triassic. They have a broad, flat carapace, which conceals the...
comprises the single family Triopsidae, containing the tadpole shrimp or shield shrimp. The two genera, Triops
Triops
Triops is a genus of small crustaceans in the order Notostraca . They are considered living fossils, with a fossil record that reaches back to the Carboniferous, .-Relatives and fossil record:...
and Lepidurus
Lepidurus
Lepidurus is the larger of the two genera of tadpole shrimp. It contains the following species:*Lepidurus apus *Lepidurus arcticus *Lepidurus batesoni Longhurst, 1955*Lepidurus bilobatus Packard, 1883...
, are considered living fossil
Living fossil
Living fossil is an informal term for any living species which appears similar to a species otherwise only known from fossils and which has no close living relatives, or a group of organisms which have long fossil records...
s, having not changed significantly in outward form since the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
. They have a broad, flat carapace, which conceals the head and bears a single pair of compound eyes. The abdomen is long, appears to be segmented and bears numerous pairs of flattened legs. The telson
Telson
The telson is the last division of the body of a crustacean. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca is often present. Together with the...
is flanked by a pair of long, thin caudal rami. Phenotypic plasticity
Phenotypic plasticity
Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...
within taxa makes species-level identification difficult, and is further compounded by variation in the mode of reproduction. Notostracans are the largest branchiopodans and are omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
s living on the bottom of temporary pools and shallow lakes.
Laevicaudata, Spinicaudata and Cyclestherida
Clam shrimp are bivalved animals which have lived since at least the DevonianDevonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
. The three groups are not believed to form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
. They have 10–32 trunk segments, decreasing in size from front to back, and each bears a pair of legs
Arthropod leg
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...
which also carry gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s. A strong muscle can close the two halves of the shell together.
Cladocera
Cladocera
Cladocera
Cladocera is an order of small crustaceans 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 long, with a down-turned head, and a carapace covering the apparently...
is an order
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 may more undescribed. They are ubiquitous in inland aquatic habitats, but rare in the oceans. Most are 0.2–6 mm (0.0078740157480315–0.236220472440945 ) 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.
Evolution
Branchiopods are considered the most primitive of the crustacean classes, and the sister group to the remaining crustaceans. The fossil record of branchiopods extends back at least into the Upper Cambrian and possibly further. The group is thought to be monophyleticMonophyly
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...
, with the Anostraca having been the first group to branch off
Cladogenesis
Cladogenesis is an evolutionary splitting event in a species in which each branch and its smaller branches forms a "clade", an evolutionary mechanism and a process of adaptive evolution that leads to the development of a greater variety of sister species...
. It is thought that the group evolved in the seas, but was forced into temporary pools
Vernal pool
Vernal pools, also called vernal ponds or ephemeral pools, are temporary pools of water. They are usually devoid of fish, and thus allow the safe development of natal amphibian and insect species...
and hypersaline lake
Hypersaline lake
A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride or other mineral salts, with saline levels surpassing that of ocean water . Specific microbial and crustacean species thrive in these high salinity environments that are otherwise...
s by the evolution of bony fishes
Osteichthyes
Osteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...
.