Mysidacea
Encyclopedia
Mysida is a group of small, shrimp
-like crustacean
s, an order
in the malacostraca
n superorder Peracarida
. Their common name opossum shrimps stems from the presence of a brood pouch
, or marsupium, in females. Mysids are mostly found in marine waters throughout the world, but are also important in some fresh
- and brackish-water ecosystems of the Northern hemisphere. Some mysids are cultured for experimental purposes and as food source for orther cultured marine organisms.
s are carried in a brood pouch, or marsupium, which is located in the thoracic
segments between the legs. They differ from other species within the superorder Peracarida by featuring statocyst
s in their uropods (located at the last abdominal segment). These are clearly seen as circular vesicles
and together with the pouch are often used as a diagnostic feature of the group. Other features include stalked compound eyes, and a carapace
that covers the head and thoracic segments.
, which means “near to shrimps”. Although in many respects mysids appear similar to some shrimps, the main characteristic separating them from the superorder Eucarida
is their lack of free-swimming larvae
. The order Mysida is extensive and currently includes approximately 160 genera
, containing more than 1000 species.
Traditionally, Mysida were united with another, externally similar group of pelagic crustaceans, the Lophogastrida
, into a broader order Mysidacea
, but that classification is currently generally abandoned.
While the previous grouping had good morphological
support, molecular studies do not corroborate the monophyly
of this group. Moreover the unity of Mysida itself has been challenged, with a suggestion to remove two of the four families, Lepidomysidae and Stygiomysidae, to form the order Stygiomysida.
and are found in both marine and freshwater environments, benthic and pelagic areas. Most mysids are free-living but a few species, mostly in the tribe Heteromysini, are commensal and are associated with sea anemone
s and hermit crab
s. Several taxa
have also been described from different groundwater habitats and caves.
The majority of Mysida are omnivore
s, feeding on algae
, detritus
, and zooplankton
. Scavenging and cannibalism
are also common, with the adults preying on their young once they emerge from the marsupium. Pelagic species are filter feeder
s while benthic species, common for the tribe Erythropini, have been observed feeding on small particles which they collect by grooming their body surface and legs. The first pair of legs in the thorax
can also function as accessory feeding limbs.
The size of a mysid brood generally correlates to body length and environmental factors such as density and food availability. Mating usually takes place at night and lasts only a few minutes. The length of time until mysids reach sexual maturity
depends on water temperature and food availability. For the species Mysidopsis bahia, this is normally 12 to 20 days. The young are released soon after, and although their numbers are usually low, the short reproductive cycle of mysid adults means a new brood can be produced every 4 to 7 days.
, having a short reproductive cycle means they can quickly reproduce in vast numbers. They can be cultured in static or flow-through systems, the latter shown to be able to carry a higher stocking density than a static system. In flow-through systems, juvenile mysids are continuously separated from the adult brood stock, to reduce mortality due to cannibalism.
Artemia (brine shrimp
) juveniles (incubated for 24 hours) are the most common food in mysid cultures, sometimes enriched with highly unsaturated fatty acid
s (HUFA) to increase the nutritional value.
Culturing mysids are thought to provide an ideal food source for many marine organisms. They are often fed to cephalopod
s, fish larvae and in commercial shrimp farms due to their small size and low costs. Their high protein and fat content also makes them a good alternative to live enriched Artemia when feeding juveniles (especially those that are difficult to maintain such as seahorse
s) and other small fauna.
Their sensitivity to water quality also makes them suitable for bioassay
s. Mysidopsis bahia and Mysidopsis almyra are used frequently to test for pesticide
s and other toxicants, with M. bahia found to be more sensitive during moulting
periods.
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
-like 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, 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...
in the malacostraca
Malacostraca
Malacostraca is the largest of the six classes of crustaceans, containing over 25,000 extant species, divided among 16 orders. Its members display a greater diversity of body forms than any other class of animals, and include crabs, lobsters, shrimp, krill, woodlice, scuds , mantis shrimp and many...
n superorder Peracarida
Peracarida
The superorder Peracarida is a large group of malacostracan crustaceans, having members in marine, freshwater, and terrestrial habitats. They are chiefly defined by the presence of a brood pouch, or marsupium, formed from thin flattened plates borne on the basalmost segments of the legs Other...
. Their common name opossum shrimps stems from the presence of a brood pouch
Brood pouch (Peracarida)
The marsupium or brood pouch, is a characteristic feature of Peracarida, including the orders Amphipoda, Isopoda and Cumacea. It is an egg chamber formed by oostegites, which are appendices which are attached to the coxae of the first pereiopods...
, or marsupium, in females. Mysids are mostly found in marine waters throughout the world, but are also important in some fresh
Fresh 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 brackish-water ecosystems of the Northern hemisphere. Some mysids are cultured for experimental purposes and as food source for orther cultured marine organisms.
Description
The majority of species are 5–25 mm (0.196850393700787–0.984251968503937 ) long, and vary in colour from pale, almost transparent, through to bright orange or brown. Unlike true shrimps, but as with other orders of Peracarida, embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s are carried in a brood pouch, or marsupium, which is located in the thoracic
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
segments between the legs. They differ from other species within the superorder Peracarida by featuring statocyst
Statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, echinoderms, cephalopods, and crustaceans. A similar structure is also found in Xenoturbella. The statocyst consists of a sac-like structure containing a mineralised mass and numerous...
s in their uropods (located at the last abdominal segment). These are clearly seen as circular vesicles
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
and together with the pouch are often used as a diagnostic feature of the group. Other features include stalked 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...
that covers the head and thoracic segments.
Systematics
The Mysida belong to the superorder PeracaridaPeracarida
The superorder Peracarida is a large group of malacostracan crustaceans, having members in marine, freshwater, and terrestrial habitats. They are chiefly defined by the presence of a brood pouch, or marsupium, formed from thin flattened plates borne on the basalmost segments of the legs Other...
, which means “near to shrimps”. Although in many respects mysids appear similar to some shrimps, the main characteristic separating them from the superorder Eucarida
Eucarida
Eucarida is a superorder of the Malacostraca, a class of the crustacean subphylum, comprising the decapods, krill and Amphionides. They are characterised by having the carapace fused to all thoracic segments, and by the possession of stalked eyes....
is their lack of free-swimming larvae
Crustacean larvae
Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow...
. The order Mysida is extensive and currently includes approximately 160 genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, containing more than 1000 species.
Traditionally, Mysida were united with another, externally similar group of pelagic crustaceans, the Lophogastrida
Lophogastrida
Lophogastrida is an order of malacostracan crustaceans in the superorder Peracarida. They are shrimp-like animals that mostly inhabit the relatively deep pelagic waters of the oceans throughout the world....
, into a broader order Mysidacea
Mysidacea
Mysida is a group of small, shrimp-like crustaceans, an order in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a brood pouch, or marsupium, in females. Mysids are mostly found in marine waters throughout the world, but are also important in...
, but that classification is currently generally abandoned.
While the previous grouping had good morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
support, molecular studies do not corroborate the monophyly
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...
of this group. Moreover the unity of Mysida itself has been challenged, with a suggestion to remove two of the four families, Lepidomysidae and Stygiomysidae, to form the order Stygiomysida.
Ecology
Mysids have a cosmopolitan distributionCosmopolitan 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...
and are found in both marine and freshwater environments, benthic and pelagic areas. Most mysids are free-living but a few species, mostly in the tribe Heteromysini, are commensal and are associated with sea anemone
Sea anemone
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...
s and hermit crab
Hermit crab
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...
s. Several taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
have also been described from different groundwater habitats and caves.
The majority of Mysida are omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
s, feeding on 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...
, 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...
, and zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
. Scavenging and cannibalism
Cannibalism
Cannibalism is the act or practice of humans eating the flesh of other human beings. It is also called anthropophagy...
are also common, with the adults preying on their young once they emerge from the marsupium. Pelagic species are filter feeder
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,...
s while benthic species, common for the tribe Erythropini, have been observed feeding on small particles which they collect by grooming their body surface and legs. The first pair of legs in the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
can also function as accessory feeding limbs.
The size of a mysid brood generally correlates to body length and environmental factors such as density and food availability. Mating usually takes place at night and lasts only a few minutes. The length of time until mysids reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
depends on water temperature and food availability. For the species Mysidopsis bahia, this is normally 12 to 20 days. The young are released soon after, and although their numbers are usually low, the short reproductive cycle of mysid adults means a new brood can be produced every 4 to 7 days.
Mysid culture
Mysids are good candidates for large scale culture as they are highly adaptive, and can occur in a wide range of habitats, and despite their low fecundityFecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
, having a short reproductive cycle means they can quickly reproduce in vast numbers. They can be cultured in static or flow-through systems, the latter shown to be able to carry a higher stocking density than a static system. In flow-through systems, juvenile mysids are continuously separated from the adult brood stock, to reduce mortality due to cannibalism.
Artemia (brine shrimp
Brine shrimp
Artemia is a genus of aquatic crustaceans known as brine shrimp. Artemia, the only genus in the family Artemiidae, has changed little externally since the Triassic period...
) juveniles (incubated for 24 hours) are the most common food in mysid cultures, sometimes enriched with highly unsaturated fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s (HUFA) to increase the nutritional value.
Culturing mysids are thought to provide an ideal food source for many marine organisms. They are often fed to cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, fish larvae and in commercial shrimp farms due to their small size and low costs. Their high protein and fat content also makes them a good alternative to live enriched Artemia when feeding juveniles (especially those that are difficult to maintain such as seahorse
Seahorse
Seahorses compose the fish genus Hippocampus within the family Syngnathidae, in order Syngnathiformes. Syngnathidae also includes the pipefishes. "Hippocampus" comes from the Ancient Greek hippos meaning "horse" and kampos meaning “sea monster”.There are nearly 50 species of seahorse...
s) and other small fauna.
Their sensitivity to water quality also makes them suitable for bioassay
Bioassay
Bioassay , or biological standardization is a type of scientific experiment. Bioassays are typically conducted to measure the effects of a substance on a living organism and are essential in the development of new drugs and in monitoring environmental pollutants...
s. Mysidopsis bahia and Mysidopsis almyra are used frequently to test for pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s and other toxicants, with M. bahia found to be more sensitive during moulting
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
periods.