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| Order: | Nassellaria Ehrenberg, 1875 |
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Nassellaria is an order of Rhizaria belonging to the class Radiolaria. [1] The organisms of this order are characterized by a skeleton cross link with a cone or ring.
Nassellaria is an order of Radiolaria under the class Polycystina. These organisms are unicellular eukaryotic heterotrophic plankton typically with a siliceous cone-shaped skeleton. The most common group of radiolarians are the polycystine radiolarians, which are divided into two subgroups: the spumellarians and the nassellarians. Both spumellarians and nassellarians are common chert-forming microfossils and are important in stratigraphical dating, as the oldest radiolarians are Precambrian in age. The nassellarians appear in the fossil record much later than their other polycystine relatives, the spumellarians. spumellarians can be seen as far back as the Precambrian, whereas nassellarians do not begin to appear until the Carboniferous. Nassellarians are believed to have been increasing in species diversity since the beginning of the Cenozoic. [2]
Nassellarians have been and continue to be some of the most remarkable and aesthetically interesting protists both alive and in the fossil record. They occupy an important role ecologically and have done so since the Precambrian. There is still much we do not know about these protists, and discovering more will require the continued interdisciplinary effort of many scientists.
The holotype morphology of the Nassellarian order as described by Anderson [2] and Boltovsky et al. [3] is of an egg-shaped central capsule (the part of the cell containing one or more nuclei, Golgi bodies, mitochondria, lysosomes, and other bodies important for cellular function) located within a porous conical skeleton made of silica. The central capsule is typically located toward the apical end of the skeleton. The basal end is usually in the shape of a hollow circle, giving the skeleton a conical look. Surrounding the central capsule, but still inside of the skeleton, is the extracapsulum. This material is primarily alveoli, gas-filled bubble-like structures that regulate the buoyancy of the organism. The alveoli are connected by a web of rhizopodia throughout the extracapsulum. Fusules connect the intracapsulum (central capsule) to the extracapsulum. Axopodia and additional fusules extend out of the basal opening and through the pores in the skeleton. These will act as feeding apparatuses for the nassellarian.
There exist three basic types of nassellarian skeletons. [2] The first is formed from the connection of three elongate spicules at a central point. The three spicules are arranged in a single plane so that they are 120 degrees apart from each other. This is typically referred to as a “tripod” structure. The second skeleton type common in nassellarians is the aforementioned conical, porous skeleton. The third type is of a ring surrounding a latticed shell. These three skeleton types can be mixed and matched to create seven skeleton categories in nassellarians. [2] Even the simplest classifications of nassellarian morphology is complicated because of the wide variety of morphologies in the nassellarian order even when compared with their sister group, the spumellarians. The innate nature of the nassellarian geometry lends itself to diversity, which may be one of the factors leading to the rapid diversification of the nassellarians in comparison to the spumellarians during the Cenozoic. [2]
Many nassellarians are segmented, meaning there are circular skeletal divisions that exist equatorially along the skeletal cone. These divisions are called strictures. [2] The strictures divide the organism into segments, typically giving it a more bulbous shape. Some nassellarians also exhibit spines from the apical end or along the lateral sides of the cone. Spines along the basal aperture of the organism are called feet. [2]
Many nassellarians house dinoflagellate symbionts within their tests. [3] The nassellarian provides ammonium and carbon dioxide for the dinoflagellate, while the dinoflagellate provides the nassellarian with a mucous membrane useful for hunting and protection against harmful invaders. [2] There is evidence from small subunit ribosomal DNA analysis of these dinoflagellate symbionts that dinoflagellate symbiosis with radiolarians evolved independently of other dinoflagellate symbioses (e.g. foraminifera). Small subunit ribosomal DNA analysis also shows evidence that no coevolution of the dinoflagellates and radiolarians has occurred. [4]
Nassellarian feeding is mainly done through extension of pseudopodia out of the basal opening. The axial projection is a very long pseudopodium that extend out of the basal aperture and is surrounded by shorter terminal projections which form a terminal cone around the axial projection. The feeding in segmented Nassellarians is done in three phases: 1) extension, 2) capture, and 3) retraction. [5] The geometry of nasselarians is quite beneficial for this feeding mechanism, as food passes through the basal aperture, which is much larger than the pores in the rest of the skeleton, which is how most spumellarians must transport food.
A second variety of nassellarians feed without using an axial projection at all. These organisms instead form a wide terminal cone, which they cast out behind them from the basal aperture like a fishing net. The three phases of feeding used by segmented nassellarians are also evident in these nassellarians. [5] These “fishing net” nassellarians are much easier to see feeding in the wild and present quite a spectacular sight.
Nassellarians feed on other plankton such as small algae, bacteria, diatoms, and small zooplankton. [2] [3] [5]
Early Paleozoic radiolarian fossil history is dominated by Spumellaria until the Carboniferous period, during which nassellarian fauna experienced a sharp increase in diversity. Nassellarian and spumellarian diversities have been relatively similar since the Mesozoic, with drops in diversity after mass extinction events and a rise in both spumellarian and nassellarian diversity during the Quaternary. [2]
Symbioses between algae and radiolarians is observed frequently in extant species, but the evolution and timing of this symbiosis is currently unknown, as the symbiotic algae do not leave behind hard skeletons to fossilize. It may be possible to answer this question using isotopic analysis, as algal symbionts preferentially uptake carbon-12, so symbiont-bearing calcareous organisms such as Foraminifera become enriched in carbon-13 compared to non symbiont-bearing calcareous organisms. [2] If fossil evidence can be gathered for isotopic ratio analysis, the time window for appearance of algal symbionts with nassellarians and/or spumellarians should be able to be restricted in geologic time.
The Acantharia are a group of radiolarian protozoa, distinguished mainly by their strontium sulfate skeletons. Acantharians are heterotrophic marine microplankton that range in size from about 200 microns in diameter up to several millimeters. Some acantharians have photosynthetic endosymbionts and hence are considered mixotrophs.
Zooplankton are the heterotrophic component of the planktonic community, having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequently, they drift or are carried along by currents in the ocean, or by currents in seas, lakes or rivers.
The Radiolaria, also called Radiozoa, are unicellular eukaryotes of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ectoplasm. The elaborate mineral skeleton is usually made of silica. They are found as zooplankton throughout the global ocean. As zooplankton, radiolarians are primarily heterotrophic, but many have photosynthetic endosymbionts and are, therefore, considered mixotrophs. The skeletal remains of some types of radiolarians make up a large part of the cover of the ocean floor as siliceous ooze. Due to their rapid change as species and intricate skeletons, radiolarians represent an important diagnostic fossil found from the Cambrian onwards.
The polycystines are a group of radiolarians. They include the vast majority of the fossil radiolaria, as their skeletons are abundant in marine sediments, making them one of the most common groups of microfossils. These skeletons are composed of opaline silica. In some it takes the form of relatively simple spicules, but in others it forms more elaborate lattices, such as concentric spheres with radial spines or sequences of conical chambers. Two of the orders belonging to this group are the radially-symmetrical Spumellaria, dating back to the late Cambrian period, and the bilaterally-symmetrical Nasselaria, whose origin is placed within the lower Devonian.
Micropaleontology is the branch of paleontology (palaeontology) that studies microfossils, or fossils that require the use of a microscope to see the organism, its morphology and its characteristic details.
Phaeodarea or Phaeodaria is a group of amoeboid cercozoan organisms. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa. They are distinguished by the structure of their central capsule and by the presence of a phaeodium, an aggregate of waste particles within the cell.
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
Tintinnids are ciliates of the choreotrich order Tintinnida, distinguished by vase-shaped shells, the name deriving from a Latin source meaning a small tinkling bell, that are called loricae, which are mostly protein but may incorporate minute pieces of minerals.
Syndinium is a cosmopolitan genus of parasitic dinoflagellates that infest and kill marine planktonic species of copepods and radiolarians. Syndinium belongs to order Syndiniales, a candidate for the uncultured group I and II marine alveolates. The lifecycle of Syndinium is not well understood beyond the parasitic and zoospore stages.
Spumellaria is an order of radiolarians in the class Polycystinea. They are ameboid protists appearing in abundance in the world's oceans, possessing a radially-symmetrical silica (opal) skeleton that has ensured their preservation in fossil records. They belong among the oldest Polycystine organisms, dating back to the lower Cambrian. Historically, many concentric radiolarians have been included in the Spumellaria order based on the absence of the initial spicular system, an early-develop structure that, by its lacking, sets them apart from Entactinaria despite their similar morphology. Living exemplars of the order feed by catching prey, such as copepod nauplii or tintinnids, on the adhesive ends of their pseudopodia extending radially from their skeleton; however, some have been observed as mixotrophs living in symbiosis with various photosynthetic algal organisms such as dinoflagellates, cyanobacteria, prasinophytes or haptophytes, which may cause their distribution to center in the greatest abundance and diversity within trophical waters.
Marine microorganisms are defined by their habitat as microorganisms living in a marine environment, that is, in the saltwater of a sea or ocean or the brackish water of a coastal estuary. A microorganism is any microscopic living organism or virus, which is invisibly small to the unaided human eye without magnification. Microorganisms are very diverse. They can be single-celled or multicellular and include bacteria, archaea, viruses, and most protozoa, as well as some fungi, algae, and animals, such as rotifers and copepods. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses as microorganisms, but others consider these as non-living.
Parvilucifera is a genus of marine alveolates that behave as endoparasites of dinoflagellates. It was described in 1999 by biologists Fredrik Norén and Øjvind Moestrup, who identified the genus among collections of Dinophysis dinoflagellates off the coast of Sweden. Initially mistaken for products of sexual reproduction, the round bodies found within these collections were eventually recognized as sporangia, spherical structures that generate zoospores of a parasitic protist. This organism was later identified as P. infectans, the type species. The examination of this organism and its close genetic relationship to Perkinsus led to the creation of the Perkinsozoa phylum within the Alveolata group.
Collodaria is a unicellular order under the phylum Radiozoa and the infrakingdom Rhizaria. Like most of the Radiolaria taxonomy, Collodaria was first described by Ernst Haeckel, a German scholar who published three volumes of manuscript describing the extensive samples of Radiolaria collected by the voyage of HMS Challenger. Recent molecular phylogenetic studies concluded that there are Collodaria contains three families, Sphaerozodae, Collosphaeridae, and Collophidilidae.
Pelagodinium béii is a photosynthetic dinoflagellate that forms a symbiotic relationship with planktonic foraminifera.
The genus Stylodictya belongs to a group of organisms called the Radiolaria. Radiolarians are amoeboid protists found as zooplankton in oceans around the world and are typically identified by their ornate skeletons.
Cornutella profunda is a species of radiolarian in the family Theoperidae and the genus Cornutella. The abundance and actual geographic span of C. profunda has not yet been fully explored, however few have been caught in various regions around the world. Samples have seen in larger numbers in the Adriatic Sea, the South China Sea, and far off the coast of Southern Africa near Namibia, and in smaller numbers in all other oceans around the world.
Marine protists are defined by their habitat as protists that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. Life originated as marine single-celled prokaryotes and later evolved into more complex eukaryotes. Eukaryotes are the more developed life forms known as plants, animals, fungi and protists. Protists are the eukaryotes that cannot be classified as plants, fungi or animals. They are mostly single-celled and microscopic. The term protist came into use historically as a term of convenience for eukaryotes that cannot be strictly classified as plants, animals or fungi. They are not a part of modern cladistics because they are paraphyletic.
Many protists have protective shells or tests, usually made from silica (glass) or calcium carbonate (chalk). Protists are a diverse group of eukaryote organisms that are not plants, animals, or fungi. They are typically microscopic unicellular organisms that live in water or moist environments.
A protist is any eukaryotic organism that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor, the last eukaryotic common ancestor, the exclusion of other eukaryotes means that protists do not form a natural group, or clade. Therefore, some protists may be more closely related to animals, plants, or fungi than they are to other protists. However, like algae, invertebrates and protozoans, the grouping is used for convenience.
Photosymbiosis is a type of symbiosis where one of the organisms is capable of photosynthesis.