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Total Categories: 6
The Müllerian law describes the precise arrangement of spines on an Acantharian, defining their positions based on lines of latitude and longitude.
Answer: True
The Müllerian law precisely details the geometric arrangement of acantharian spines, positioning them at the intersections of specific lines of latitude and longitude.
The endoplasm of an Acantharian cell contains the main organelles and multiple nuclei, while the ectoplasm is involved in prey capture and digestion.
Answer: True
The endoplasm houses organelles and nuclei, while the ectoplasm contains cytoplasmic extensions for prey capture and food vacuoles for digestion, confirming the statement.
The periplasmic cortex in Acantharians is composed of a single, continuous membrane that directly connects to the spines.
Answer: False
The periplasmic cortex is composed of twenty distinct microfibril plates, not a single continuous membrane, and is connected to the spines by contractile myonemes.
Myonemes in Acantharians primarily function in nutrient absorption from the surrounding water.
Answer: False
Myonemes in Acantharians are contractile structures that primarily function in buoyancy control by expanding and contracting the ectoplasm, not nutrient absorption.
The microfibril mesh capsular wall in Acantharians separates the ectoplasm from the periplasmic cortex.
Answer: False
The microfibril mesh capsular wall separates the endoplasm from the ectoplasm, while the periplasmic cortex surrounds the ectoplasm, not separated by the capsular wall.
Cytoplasmic extensions in the ectoplasm are primarily used for buoyancy control.
Answer: False
Cytoplasmic extensions in the ectoplasm are primarily utilized for prey capture, whereas contractile myonemes are responsible for buoyancy control.
Acantharians typically range in size from a few nanometers up to several micrometers.
Answer: False
Acantharians typically range in size from approximately 200 microns up to several millimeters, which is significantly larger than a few nanometers or micrometers.
What is the primary distinguishing feature of Acantharia among radiolarian protozoa?
Answer: Their skeletons composed of strontium sulfate
Acantharians are uniquely distinguished among radiolarian protozoa by their skeletons, which are composed of strontium sulfate.
What is the function of contractile myonemes in Acantharians?
Answer: To assist in buoyancy control by expanding and contracting the ectoplasm
Contractile myonemes in Acantharians are crucial for buoyancy control, enabling the ectoplasm to expand and contract, thereby regulating the cell's volume and position in the water column.
What is the typical size range of Acantharians?
Answer: Approximately 200 microns up to several millimeters
Acantharians are marine microplankton that typically range in size from approximately 200 microns in diameter up to several millimeters.
How many distinct plates make up the periplasmic cortex in Acantharians?
Answer: Twenty
The periplasmic cortex, which surrounds the ectoplasm, is composed of twenty distinct microfibril plates.
What does the Müllerian law describe regarding Acantharians?
Answer: The precise arrangement of their spines
The Müllerian law specifically describes the highly precise and geometric arrangement of spines on an Acantharian, defining their positions based on lines of latitude and longitude.
What is the role of food vacuoles located in the ectoplasm?
Answer: To digest captured prey
Food vacuoles, located within the ectoplasm, are specifically responsible for the digestion of captured prey, processing the nutrients for the acantharian.
Acantharian skeletons are primarily composed of calcium carbonate, similar to many other marine plankton.
Answer: False
Acantharian skeletons are uniquely composed of strontium sulfate, not calcium carbonate, distinguishing them from many other marine plankton.
Acantharian skeletons readily fossilize due to the abundance of strontium sulfate in seawater, making them valuable for paleontological studies.
Answer: False
Acantharian skeletons do not fossilize because strontium sulfate is scarce in seawater, causing the crystals to dissolve after the organism's death.
Celestine, the mineral form of strontium sulfate in Acantharian skeletons, is known for its high density, which aids in rapid sinking.
Answer: True
Celestine, the strontium sulfate mineral in Acantharian skeletons, is the heaviest mineral in the ocean, and its high density acts as mineral ballast, facilitating rapid sinking to bathypelagic depths.
The common name for the strontium sulfate mineral found in Acantharian skeletons is gypsum.
Answer: False
The common name for the strontium sulfate mineral found in Acantharian skeletons is celestine, not gypsum.
What is the mineral form of strontium sulfate that constitutes Acantharian skeletons?
Answer: Celestine
The mineral form of strontium sulfate (SrSO4) that constitutes Acantharian skeletons is celestine.
According to the source, why do Acantharian skeletons not fossilize?
Answer: Strontium sulfate is scarce in seawater, causing the crystals to dissolve after death.
Acantharian skeletons do not fossilize because strontium sulfate is very scarce in seawater, leading to the dissolution of the crystals after the organism's death.
What does the high density of celestine in Acantharian shells ensure?
Answer: Rapid settling to bathypelagic depths
The high density of celestine, the strontium sulfate mineral in Acantharian skeletons, functions as mineral ballast, ensuring rapid settling of the organisms to bathypelagic depths.
What is the primary component of Acantharian skeletons?
Answer: Strontium sulfate
Acantharian skeletons are primarily and uniquely composed of strontium sulfate, distinguishing them from other radiolarians that typically have silica skeletons.
The Holacanthida order is characterized by having 20 radial spicules that are loosely attached at the center of the cell.
Answer: False
The Holacanthida order is characterized by 10 diametric spicules without a central junction, whereas the description of 20 radial spicules loosely attached at the center of the cell applies to the Chaunacanthida order.
The morphological classification of Acantharians consistently shows monophyletic groups that perfectly align with molecular phylogenetic trees.
Answer: False
While morphological classification generally agrees with molecular phylogenetic trees, the morphologically defined groups are often polyphyletic, meaning they do not perfectly align as monophyletic groups.
Based on molecular data, Arthracanthida and Symphacanthida are believed to have evolved first among Acantharian clades, possessing the simplest skeletons.
Answer: False
Molecular data suggest that Holacanthida evolved first, followed by Chaunacanthida, while Arthracanthida and Symphacanthida, with their more complex skeletons, are believed to have evolved more recently.
Acantharians are classified within the Subphylum Radiolaria, and their class was established by Haeckel in 1881.
Answer: True
Acantharians are indeed classified under the Subphylum Radiolaria, and the Class Acantharia was established by Haeckel in 1881, later emended by Mikrjukov in 2000.
The Class Acantharia was initially classified by Mikrjukov in 2000 and later emended by Haeckel in 1881.
Answer: False
The Class Acantharia was initially classified by Haeckel in 1881 and later emended by Mikrjukov in 2000, reversing the order presented in the statement.
The Symphyacanthida order is characterized by having 20 radial spicules that form a tight central junction within the cell.
Answer: True
The Symphyacanthida order is indeed defined by its 20 radial spicules that converge to form a tight central junction within the cell.
Which of the following Acantharian orders is characterized by having 10 diametric spicules that are simply crossed without a central junction?
Answer: Holacanthida
The Holacanthida order is characterized by 10 diametric spicules that are simply crossed without forming a central junction.
What is the hypothesized evolutionary order of Acantharian clades, from earliest to most recent, based on molecular data and skeleton complexity?
Answer: Holacanthida → Chaunacanthida → Arthracanthida and Symphacanthida
Molecular data suggest an evolutionary progression from Holacanthida (earliest) to Chaunacanthida, and then to Arthracanthida and Symphacanthida (most recent and complex skeletons).
Which molecular clades are associated with the Arthracanthida and Symphacanthida orders?
Answer: Clades E and F
The Arthracanthida and Symphacanthida orders are associated with molecular clades E and F, respectively.
Who initially classified the Class Acantharia?
Answer: Haeckel in 1881
The Class Acantharia was initially classified by Haeckel in 1881, with an emendation later provided by Mikrjukov in 2000.
Which Acantharian order is characterized by having 20 radial spicules that are loosely attached at the center of the cell?
Answer: Chaunacanthida
The Chaunacanthida order is characterized by having 20 radial spicules that are loosely attached at the center of the cell.
Which of the following is a key characteristic used for classifying Acantharians taxonomically?
Answer: The manner in which their spines are joined at the center of the cell
A primary characteristic used for the taxonomic classification of Acantharians is the specific manner in which their spines are joined at the center of the cell.
What is the scientific classification of Acantharia at the Class level?
Answer: Class Acantharia
Within the biological hierarchy, Acantharians are classified as the Class Acantharia, a classification established by Haeckel in 1881.
Acantharians are exclusively autotrophic, meaning they produce their own food through photosynthesis.
Answer: False
Acantharians are heterotrophic marine microplankton, and many are mixotrophic due to hosting photosynthetic endosymbionts, meaning they are not exclusively autotrophic.
All Acantharian species are known to host single-celled algae within their inner cytoplasm.
Answer: False
While many acantharians host single-celled algae, particularly in certain clades (some B, all E and F), it is not true that *all* species are known to do so.
Photosymbiosis is hypothesized to allow acantharians to thrive in low-nutrient oceanic regions and provide energy for maintaining their skeletons.
Answer: True
Photosymbiosis is indeed hypothesized to enable acantharians to flourish in oligotrophic oceanic environments and to supply the metabolic energy required for the upkeep of their strontium sulfate skeletons.
The symbiotic relationship between acantharians and their algal partners is definitively known to be mutually beneficial for both organisms.
Answer: False
It is not definitively known if the symbiotic relationship is always mutually beneficial; there is a possibility that acantharians exploit their algal symbionts, potentially digesting them after utilizing their photosynthetic products.
Clade E and F acantharians primarily host diverse dinoflagellate genera as symbionts.
Answer: False
Clade E and F acantharians primarily host symbionts from the haptophyte genus *Phaeocystis*, whereas diverse dinoflagellate genera are typically hosted by symbiotic Holacanthida acantharians.
The observed mismatch between internal and external symbiont communities in Clade F acantharians suggests they are non-selective in symbiont acquisition.
Answer: False
The mismatch between internal and external symbiont communities in Clade F acantharians actually suggests that these organisms are *selective* in choosing and maintaining their symbionts, rather than being non-selective.
Which of the following describes the nutritional strategy of some acantharians that host photosynthetic endosymbionts?
Answer: Mixotrophic
Acantharians that host photosynthetic endosymbionts are considered mixotrophs, as they acquire energy through both heterotrophy (consuming prey) and autotrophy (from their symbionts' photosynthesis).
What is the proposed exchange of nutrients between acantharians and their algal symbionts?
Answer: Acantharians provide nitrogen and phosphorus; algae provide sugars.
The proposed nutrient exchange involves acantharians providing nitrogen and phosphorus to their algal symbionts, while the algae, in turn, produce sugars through photosynthesis for the acantharians.
Where are algal symbionts maintained in symbiotic Acantharian species?
Answer: Within the endoplasm
In symbiotic Acantharian species, the algal symbionts are maintained within the endoplasm, which is separated from the ectoplasm by a capsular wall.
Which of the following is NOT a hypothesized advantage for acantharians engaging in photosymbiosis?
Answer: Increased resistance to predation
Hypothesized advantages of photosymbiosis for acantharians include thriving in low-nutrient regions and acquiring energy for skeleton maintenance, but increased resistance to predation is not mentioned as a benefit.
What types of symbionts are primarily hosted by Clade E and F acantharians?
Answer: Haptophyte genus *Phaeocystis*
Clade E and F acantharians primarily host symbionts from the haptophyte genus *Phaeocystis*, although *Chrysochromulina* symbionts are also sometimes observed.
What does the observed mismatch between internal and external symbiont communities in Clade F acantharians suggest?
Answer: That acantharians are selective in choosing their symbionts and maintain them long-term.
The observed mismatch between internal and external symbiont communities in Clade F acantharians suggests that these organisms are selective in their symbiont acquisition and maintain these symbionts for extended periods.
Which of the following is NOT a genus of dinoflagellate symbiont hosted by symbiotic Holacanthida acantharians?
Answer: *Phaeocystis*
Symbiotic Holacanthida acantharians host diverse dinoflagellate genera such as *Pelagodinium*, *Heterocapsa*, and *Azadinium*, but *Phaeocystis* is primarily hosted by Clade E and F acantharians.
Adult Acantharians are typically uninucleated, meaning they possess a single nucleus.
Answer: False
Adult Acantharians are typically multinucleated, possessing multiple nuclei within their cells, rather than being uninucleated.
The fusion of Acantharian swarmer cells to produce a new acantharian has been extensively observed and documented.
Answer: False
The fusion of Acantharian swarmer cells to form a new acantharian has not yet been observed, indicating a gap in the complete understanding of their reproductive cycle.
The primary obstacle to studying Acantharian life cycles is their extremely small size, making observation impossible.
Answer: False
The primary obstacle to studying Acantharian life cycles is the inability to 'close the lifecycle' and maintain them in culture through successive generations, rather than their size making observation impossible.
Acantharians with diametric spicules or loosely attached radial spicules are capable of forming cysts.
Answer: True
Acantharians belonging to the Holacanthida and Chaunacanthida orders, characterized by diametric or loosely attached radial spicules, respectively, are indeed capable of encystment.
Reproduction in Acantharians is thought to occur through the formation of swarmer cells, which can be released from both cysts and non-encysted cells.
Answer: True
Reproduction in Acantharians is indeed believed to involve the formation of swarmer cells, which have been observed to be released from both cysts and non-encysted cells under laboratory conditions.
Releasing swarmer cells in deeper water is believed to decrease the survival chances of Acantharian juveniles due to increased pressure.
Answer: False
Releasing swarmer cells in deeper water is hypothesized to *improve* the survival chances of Acantharian juveniles, possibly by offering a more stable or protected environment, rather than decreasing them due to pressure.
What is a characteristic feature of adult Acantharians in terms of their cellular structure?
Answer: They are typically multinucleated.
Adult Acantharians are characterized by being typically multinucleated, meaning their cells contain multiple nuclei.
What is the primary obstacle hindering the comprehensive study of Acantharian life cycles?
Answer: The inability to 'close the lifecycle' and maintain them in culture
The primary obstacle to a comprehensive study of Acantharian life cycles is the persistent inability to 'close the lifecycle' and successfully maintain these organisms in culture through successive generations.
What is the main challenge in observing the full life cycle of Acantharians?
Answer: Their inability to be maintained in culture through successive generations
The main challenge in observing the full life cycle of Acantharians is the inability to 'close the lifecycle' and successfully maintain these organisms in laboratory cultures through successive generations.
Which of the following statements about Acantharian reproduction is true?
Answer: Reproduction is thought to occur through the formation of swarmer cells, released from cysts or non-encysted cells.
Reproduction in Acantharians is believed to involve the formation of swarmer cells, which can be released from both cysts and non-encysted cells, although the fusion of these cells has not yet been observed.
High settling fluxes of acantharian cysts have been observed to contribute significantly to the transport of organic matter to the deep sea.
Answer: True
Observations in ocean basins like the Iceland Basin and Southern Ocean confirm that high settling fluxes of acantharian cysts contribute substantially to the vertical transport of organic carbon to the deep sea.
What is the significance of acantharian cysts being found in sediment traps?
Answer: It suggests their role in vertical transport of biomass to deep water.
The frequent discovery of acantharian cysts in sediment traps indicates their crucial role in the vertical transport of biomass and organic matter to deep-water environments.