Kraken | |
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Kraken carinae | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
Clade: | SAR |
Phylum: | Cercozoa |
Class: | Imbricatea |
Subclass: | Krakenia Cavalier-Smith 2018 |
Order: | Krakenida Dumack et al. 2017 ex Cavalier-Smith 2018 |
Family: | Krakenidae Dumack et al. 2017 |
Genus: | Kraken Dumack et al. 2016 |
Type species | |
Kraken carinae Dumack et al. 2016 |
Kraken is a genus of amoebae within the Cercozoa, containing the sole species Kraken carinae. These amoebae are characterized by a small round cell body and a network of thin and very long filopodia that can reach up to a mm in diameter. Kraken amoebae feed on bacteria and live in freshwater and soil systems.
Kraken was named after the German word Krakonen, which is the name used to refer to the Norse mythological monster. Kraken was named as such due to the method of feeding, in which the large network of branching filopodia grab bacteria and transports it to the cell body. The mythological monster Kraken was told to catch its prey with one of its many arms in a similar manner. [1]
Kraken is a recently discovered genus, having first been described in 2016 at the University of Koln. Thomas Cavalier-Smith established the phylum Cercozoa in 1998, which consists of flagellates and filose amoebae that are widely morphologically diverse. Genetic analysis and morphological characteristics place the Genus Kraken as a Cercozoan. [2]
Currently, the genus consists of a single species, Kraken carinae. Through genetic analysis, ultrastructure data, and phylogenetic analysis, Kraken could not accurately be placed in an existing family, thus the new family Krakenidae was established. Currently, it is being considered to establish the new order Krakenida. [3]
Kraken has only been observed and collected from Europe and Antarctica, though it is suspected to be distributed worldwide. Kraken is found in dry surface soil sediment, most prevalently in bacteria rich environments. Members have also been collected in freshwater lakes and aquatic moss pillars in the Antarctic region, suggesting a wider possible range of tolerance and habitability. [1] The full extent of Krakens preferred environment has not been studied.
Some organisms have also been collected in agricultural crops, particularly growing around wheat. This may suggest some ecosystem interactions that have yet to be studied further. [1]
Kraken preys predominantly on bacteria.
Kraken consists of a round cell body, that is typically 7-9 μm in diameter. One large filopodium originates from the basal end of the cell body, and expands up to 300 μm. The filopodium branches extensively and forms a very large network, expanding the diameter of the organism to over 500 μm. The filopodia are thin, and taper at the ends. Kraken are very fragile. When the cell body is slightly mechanically disturbed in a lab setting, the filopodia retract close to the cell body. This often leads to cell death. [1]
The filopodia are used to catch prey, mainly bacteria. The filopodia catch and attach prey through their vast network. These bacteria then glide through or along the filopodia to the cell body for digestion. [1]
The cell body does not have any covering, instead it is surrounded by scales. These scales are formed in the cisternae of the Golgi apparatus, and carried to the surface. The scales are made of silica, are evenly distributed around the cell body, and do not overlap. [3]
Typically Kraken has only one nucleus, though binucleate organisms have been observed. The organisms means of reproduction have not been studied, and whether it reproduces by sexual or asexual means is unknown. The nuclei contain one large round nucleolus each. [3]
The cell body contains a contractile vacuole, a single large food vacuole, and several small granules. Also present is various numbers of mitochondria with flat shaped cristae. The periphery of the cell body is lined with extrusomes, and consists of an internal capsule that discharges and catches prey. [3]
Kraken has the ability to encyst when dormant.
Kraken movement is relatively slow. There are 3 highly unusual methods of movement. The filopodium can grip the substrate and carry the cell body above the surface by a swaying locomotive action. The cell body can also move along a deeply branched filopodia. In a unique manner, Kraken can also completely disassemble its cell body and transport cell material through the filopodia network, where it is then deposited and reassembled elsewhere. This serves to move the cell body to the distal ends of the filopodia, which can then reposition and branch to new areas. [3]
The family Vampyrellidae is a subgroup of the order Vampyrellida within the supergroup Rhizaria. Based on molecular sequence data, the family currently comprises the genus Vampyrella, and maybe several other vampyrellid amoebae. The cells are naked and characterised by radiating, filose pseudopodia and an orange colouration of the main cell body.
Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eukaryotic group to be recognized mainly through molecular phylogenies. They are the natural predators of many species of bacteria. They are closely related to the phylum Retaria, comprising amoeboids that usually have complex shells, and together form a supergroup called Rhizaria.
The Rhizaria are a diverse and species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthetic, but many foraminifera and radiolaria have a symbiotic relationship with unicellular algae. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has been described. This group was used by Cavalier-Smith in 2002, although the term "Rhizaria" had been long used for clades within the currently recognized taxon.
The euglyphids are a prominent group of filose amoebae that produce shells or tests that in most described species is reinforced by siliceous scales, plates, and sometimes spines, but this reinforcement is absent in other species. These elements are created within the cell and then assembled on its surface in a more or less regular arrangement, giving the test a textured appearance. There is a single opening for the long slender pseudopods, which capture food and pull the cell across the substrate.
Monadofilosa is a grouping of Cercozoa. These organisms are single-celled amoeboid protists.
Thecofilosea is a class of unicellular testate amoebae belonging to the phylum Cercozoa. They are amoeboflagellates, organisms with flagella and pseudopodia, distinguished from other cercozoa by their scale-lacking test composed of organic material. They are closely related to the Imbricatea, a group of testate amoebae with tests composed of inorganic silica scales.
The sarcomonads or class Sarcomonadea are a group of amoeboid biciliate protists in the phylum Cercozoa. They are characterized by a propensity to move through gliding on their posterior cilium or through filopodia, a lack of scales or external theca, a soft cell surface without obvious cortical filamentous or membranous skeleton, two cilia without scales or hairs, tubular mitochondrial cristae, near-spherical extrusomes, and a microbody attached to the nucleus.
The vampyrellids, colloquially known as vampire amoebae, are a group of free-living predatory amoebae classified as part of the lineage Endomyxa. They are distinguished from other groups of amoebae by their irregular cell shape with propensity to fuse and split like plasmodial organisms, and their life cycle with a digestive cyst stage that digests the gathered food. They appear worldwide in marine, brackish, freshwater and soil habitats. They are important predators of an enormous variety of microscopic organisms, from algae to fungi and animals. They are also known as aconchulinid amoebae.
Rigifila is a genus of free-living single-celled eukaryotes, or protists, containing the sole species Rigifila ramosa. It is classified within the monotypic family Rigifilidae. Along with Micronucleariidae, it is a member of Rigifilida, an order of basal eukaryotes within the CRuMs clade. It differs from Micronuclearia by having two proteic layers surrounding their cytoplasm instead of a single one, and having more irregular mitochondrial cristae, among other morphological differences.
Vampyrella is a genus of amoebae belonging to the vampyrellid endomyxans usually ranging from 30-60 μm. Members of the genus alternate between two life stages: a free-living trophozoite stage and a cyst stage in which mitosis occurs. This taxon has received a great deal of attention due to their peculiar feeding behaviour of perforating the cell wall of algal cells and drawing out the contents for nourishment.
Neocercomonas is a protist genus of the order Cercomonadida. It consists of single-celled bacteriophagous organisms that usually live on or nearby terrestrial plants, both above and belowground. Species are biflagellate and may grow up to 60 micrometers long, with a trailing tail-like mass of protoplasm at their posterior end and a pair of roots connecting their posterior flagellum to the cytoskeleton.
Vampyrella lateritia is a freshwater species of predatory amoebae that feeds on species of algae and is known for its specialized feeding strategy of removing, digesting, and ingesting the cellular contents of its prey. It is the type species of the genus Vampyrella and has been identified in numerous locations around the world including Brazil, Germany, and the eastern United States. Along with Vampyrella pendula, its genome was sequenced in 2012.
Nanofila is a genus of marine heterotrophic protists of the phylum Cercozoa. It is the only genus in the family Nanofilidae. It is a monotypic genus, with the sole species N. marina.
Mesofila is a genus of freshwater heterotrophic protists of the phylum Cercozoa. It is the only genus in the family Mesofilidae. It is a monotypic genus, with the sole species M. limnetica.
Minimassisteria is a marine bacterivorous genus of protists with only one species, M. diva, that presents three different lifestyle forms. It has a widespread geographic distribution. It is an amoeboflagellate most closely related to Massisteria, and together comprise the family Massisteriidae.
Orciraptor is a genus of heterotrophic protists, containing the single species Orciraptor agilis. It belongs to the family Viridiraptoridae, in the phylum Cercozoa.
Aurigamonas is a genus of predatory protists of an unusual cell structure, with two flagella and numerous haptopodia. It is a monotypic genus containing the single species Aurigamonas solis. It is the only genus of the family Aurigamonadidae.
Rhogostoma minus is a species of thecate amoeba that belongs to the phylum Cercozoa. It was first described by Belar in 1921. These amoebae are heterotrophic, which means that they consume other organisms for nutrition. The cells of Rhogostoma minus are typically between 8 and 12 μm in diameter and are surrounded by a protective organic covering called a theca. The theca has a unique cleft-like opening that allows the amoebae to extend and retract thread-like projections called filose pseudopodia. The amoebae move along surfaces by pulling themselves forward using their pseudopodia.
Rhogostomidae is a family of thecate amoebae with a ventral cleft-like aperture. Their theca is thin and flexible and adheres to the cell. The cleft-like aperture allows them to extend and retract their filose pseudopodia, which they use to move and feed. They are primarily feeding on bacteria, but they are also known to consume yeasts and algae. The family contains three genera: Capsellina, Sacciforma, and Rhogostoma.
Limnofila is a genus of heterotrophic protists that live in freshwater habitats and feed on bacteria. They are also present in the soil ecosystem, where they play an important role as predators of bacteria. They are classified as a single family Limnofilidae and order Limnofilida.