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''Henneguya zschokkei'' or ''Henneguya salminicola'' is a species of a
myxosporea Myxosporea is a class of microscopic parasites, belonging to the Myxozoa clade within Cnidaria. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate (generally an annelid but sometimes a bryozoa ...
n
endoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
. It afflicts several
salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
in the genus ''
Oncorhynchus ''Oncorhynchus'' is a genus of fish in the family Salmonidae; it contains the Pacific salmon and Pacific trout. The name of the genus is derived from the Greek ὄγκος (ónkos, “lump, bend”) + ῥύγχος (rhúnkhos, “snout”), in r ...
''. It causes milky flesh or tapioca disease. ''H. zschokkei'' is notable for its absence of
mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
,
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
,
aerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
and its reliance on an as yet undiscovered energy metabolism.


Description

''Henneguya salminicola'' is found in fish as an ovoid spore with two anterior polar capsules and two long caudal appendages. Individuals are very small (about 10 micrometers in diameter), but are found aggregated into
cyst A cyst is a closed sac, having a distinct envelope and cell division, division compared with the nearby Biological tissue, tissue. Hence, it is a cluster of Cell (biology), cells that have grouped together to form a sac (like the manner in which ...
s 3–6 mm in diameter at any place in the muscle mass.


Unknown metabolism

''Henneguya salminicola'' is the only known multicellular
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
that does not rely on the
aerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
of
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
. It lacks a
mitochondrial genome Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
and therefore
mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...
, making it one of the only members of the
eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
animal kingdom to shun oxygen as the foundation of its
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
. The means by which ''H. zschokkei'' utilizes chemical energy for the sustenance of its life is not yet known.; Lay summary: ''H. zschokkei'' is ultimately a highly derived cnidarian. This obligate internal parasite so little resembles other multicellular animals that it, along with many other species in class
Myxosporea Myxosporea is a class of microscopic parasites, belonging to the Myxozoa clade within Cnidaria. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate (generally an annelid but sometimes a bryozoa ...
, were initially categorized as
protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
. It is nevertheless most closely related to
jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...
. This species, like most myxosporeans, lacks many of the diagnostic criteria that identify cnidarians. It is without nervous,
epithelial Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...
, gut or
muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
cells of any kind. This parasite has not only lost its mitochondria and the
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
residing in them, but also the nuclear genes that code for mitochondrial reproduction. What genetic instructions for these functions remain are in the form of useless
pseudogenes Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by DNA duplication or indirectly by reverse transcription of an mRNA transcript. Pseudogenes are ...
.


Origins

The origin and cause of its highly reduced genome are not yet known. While
eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
s are known for aerobic respiration, a few unicellular lineages native to
hypoxic Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the t ...
environments have lost this capacity. In the absence of oxygen these single-celled organisms have lost portions of their genome governing aerobic respiration. Such eukaryotes have developed mitochondria-related organelles (MROs), which fulfil many of the functions of conventional mitochondria. However there is no evidence for such adaptation in the multicellular ''H. zschokkei''. One theory explaining the highly unsual
habit A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.
of ''H. zschokkei'' and its fellow myxosporeans invokes the
cancers Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...
of cnidarians. On this explanation, animals such as ''H. zschokkei'' were originally cancerous growths in free-swimming jellyfish that escaped their parent organism and thereafter became a separate species parasitizing other animals. Such an origin is referred to as a SCANDAL (Speciated by CANcer Development in AnimaLs).


Hosts

Known hosts of ''Henneguya zschokkei'' include: * ''Oncorhynchus gorbuscha'' (
Pink salmon Pink salmon or humpback salmon (''Oncorhynchus gorbuscha'') is a species of anadromous fish in the salmon family. It is the smallest and most abundant of the Pacific salmon. The scientific species name is based on the Russian common name for ...
) * ''Oncorhynchus keta'' (
Chum salmon The chum salmon (''Oncorhynchus keta''), also known as dog salmon or keta salmon, is a species of anadromous salmonid fish from the genus '' Oncorhynchus'' (Pacific salmon) native to the coastal rivers of the North Pacific and the Beringian A ...
) * ''Oncorhynchus kisutch'' (
Coho salmon The coho salmon (''Oncorhynchus kisutch;'' Karuk: achvuun) is a species of anadromous fish in the salmon family (biology), family and one of the five Pacific salmon species. Coho salmon are also known as silver salmon or "silvers". The scientif ...
) * ''Oncorhynchus nerka'' ( Sockeye salmon) *
Anadromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousan ...
forms of ''Oncorhynchus mykiss'' (
Rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...
) * ''Oncorhynchus tshawytscha'' (
Chinook salmon The Chinook salmon (''Oncorhynchus tshawytscha'') is the largest and most valuable species of Pacific salmon in North America, as well as the largest in the genus ''Oncorhynchus''. Its common name is derived from the Chinookan peoples. Other ve ...
) * ''Salmo salar'' (
Atlantic Salmon The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to a meter in length. Atlantic salmon are ...
)


See also

;Taxa * ''
Cryptosporidium parvum ''Cryptosporidium parvum'' is one of several species that cause cryptosporidiosis, a parasitic disease of the mammalian intestinal tract. Primary symptoms of ''C. parvum'' infection are acute, watery, and nonbloody diarrhea. ''C. parvum'' infect ...
'', a protist (Apicomplexa) without genes in its mitochondria * ''
Mastigamoeba ''Mastigamoeba'' is a genus of peolobionts, and treated by some as members of the Archamoebae group of protists. ''Mastigamoeba ''are characterized as anaerobic, amitochondriate organisms that are polymorphic. Their dominant life cycle stage i ...
'', an anaerobic protist (Amoebozoa) without mitochondria * ''
Monocercomonoides ''Monocercomonoides'' is a genus of flagellate Excavata belonging to the order Oxymonadida. It was established by Bernard V. Travis and was first described as those with "polymastiginid flagellates having three anterior flagella and a trailin ...
'', a protist (
Metamonad The metamonads are microscopic eukaryotic organisms, a large group of flagellate amitochondriate Loukozoa. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads a ...
) without mitochondria *
Loricifera Loricifera (from Latin, '' lorica'', corselet (armour) + ''ferre'', to bear) is a phylum of very small to microscopic marine cycloneuralian sediment-dwelling animals that had been determined to be 37 described species, in 9 genera, bu ...
, other metazoans; some species don't require oxygen and may also lack mitochondria ;Structures *
hydrogenosome A hydrogenosome is a membrane-enclosed organelle found in some anaerobic ciliates, flagellates, and fungi. Hydrogenosomes are highly variable organelles that have presumably evolved from protomitochondria to produce molecular hydrogen and ATP in ...
, an organelle of some anaerobic taxa


References


Further reading

* * * *


External links

* *
GBIF The Global Biodiversity Information Facility (GBIF) is an international organisation that focuses on making scientific data on biodiversity available via the Internet using web services. The data are provided by many institutions from around the ...

''Henneguya salminicola'' Ward, 1919
Id:6881057, source:
World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive list of names of marine organisms. Content The content of the registry is edited and maintained by scientific specialist ...
*
GBIF The Global Biodiversity Information Facility (GBIF) is an international organisation that focuses on making scientific data on biodiversity available via the Internet using web services. The data are provided by many institutions from around the ...

''Henneguya zschokkei'' Ward, 1919
Id:6881028, source: Artsnavnebasen {{Taxonbar, from=Q16983022 Animal parasites of fish Myxobolidae Veterinary parasitology