Hyalospheniidae is a family of arcellinidtestate amoebae and the sole family of the infraorder Hyalospheniformes. Commonly referred to as "hyalospheniids", these lobose amoebae are characterized by their ability to generate a shell composed of either organic matter or siliceous particles that may be recycled from euglyphid amoebae. They inhabit soil or freshwater habitats, and are abundant on Sphagnum mosses.
Hyalospheniid amoebae originated after the middle Devonian, around 370 million years ago. They are considered important bioindicators, and are frequently used for environmental monitoring. Their fossils are studied to investigate the paleoecology of prehistoric wetland habitats. The classification of hyalospheniids has changed several times since the 19th century based on morphological criteria. Initially classified as two separate families, Hyalospheniidae and Nebelidae, they were later proven to be synonymous through phylogenetic analyses.
Morphology
Hyalospheniidae are testate amoebae—unicellularamoeboidprotists that generate mineral agglutinated shells. They are characterized by ovoid, pyriform, vase or flask-shaped shells, which are laterally compressed.[7][8] Shell construction and composition varies substantially within the family. It can be either entirely secreted by their own cells and composed of an organic matrix (e.g. Hyalosphenia), or have additional non-organic siliceous scales. These mineral scales can also be self-secreted (e.g. Quadrulella), or can be recycled from the shell plates of small euglyphid amoebae or other similar material such as diatom frustules (e.g. Apodera, Padaungiella, Nebela).[7] The trait of recycling shell plates from euglyphids is known as "kleptosquamy", and appears to be an ancestral trait within the family.[1]
The two main types of shell construction among hyalospheniids
Ecology
Hyalospheniid amoebae are considered important bioindicators in environmental monitoring studies. Their sensitivity to environmental changes, such as atmospheric pollution,[9] make them reliable indicators of hydrological changes. Together with the preservation of their shells over thousands of years, their environmental sensitivity gives them a prominent role in the reconstruction of the paleoclimate in peatlands, bogs and fens.[7]
Position of hyalosphenids in the arcellinid phylogeny.[12]
Hyalospheniidae is a family of Arcellinida, an order of lobosetestate amoebae within the eukaryoticsupergroupAmoebozoa. In contrast to filose testate amoebae, found within the supergroup Rhizaria (e.g. euglyphid amoebae), they present thicker pseudopods with blunt ends. It is the only family of the infraorder Hyalospheniformes, which belongs to the suborder Glutinoconcha. Glutinoconcha, which contains the majority of arcellinid species, evolved from a common ancestor with mineral agglutinated shells, in contrast to the organic shells of Organoconcha. In particular, Hyalospheniformes and Volnustoma, a different infraorder of Glutinoconcha, both evolved from ancestors with xenosomic agglutinated shells (i.e. composed of particles incorporated from an external source).[4][12]
Through molecular clock approximations, the age of Hyalospheniidae was estimated in 2015 to be around 370 million years old, between the Devonian and the early Carboniferous. This molecular reconstruction suggests that hyalospheniids diversified after the middle Devonian, when the diversification of land plants formed extensive forests with an abundant production of organic matter and soils. Kleptosquamy, the ability of hyalosphenid amoebae to "steal" test scales from their prey, euglyphid amoebae, is hypothesized to be an ancestral trait within the family. This working hypothesis is based on the presence of kleptosquamy on most hyalospheniids.[1] In addition to the molecular clock estimates, it has been suggested that 750–million-year-old vase-shaped microfossils could belong to this family.[13][7][14]
Systematics
History of taxonomy
There has been several attempts at classifying Hyalospheniidae among testate amoebae, as well as its internal classification. American paleontologistJoseph Leidy, in 1874, was possibly the first to notice common characteristics between the cells. He described the vase-shaped tests as composed of small siliceous particles ("discoid plates and minute rods") caught within an organic matrix, interpreted to be originated by the amoeba ("intrinsic"). He grouped those species within the genus Nebela, restricting them from the previously known genus of testate amoebae Difflugia. Instead, he described Difflugia species as having a "test composed of extraneous bodies, such as particles of quartzose sand, and diatom cases".[15][7]
^Kosakyan, Anush; Gomaa, Fatma; Lara, Enrique; Lahr, Daniel J.G. (2016). "Current and future perspectives on the systematics, taxonomy and nomenclature of testate amoebae". European Journal of Protistology. 55B (Pt B): 105–117. doi:10.1016/j.ejop.2016.02.001. PMID27004416.
^ abTaranek KJ (1882). "Monographie der Nebeliden Böhmens. Ein Beitrag zur Kenntnis der Süsswasser Monothalamien" [Monograph of the Nebelids of Bohemia. A contribution to the knowledge of freshwater monothalamids]. Abhandlungen der Königlichen Böhmischen Gesellschaft der Wissenschaften (in German). VI: 1–56.
^Zagumyonnaya ON, Philippov DA, Zagumyonnyi DG, Komarov AA, Tsyganov AN, Tikhonenkov DV (2023). "Changes in Testate Amoeba Assemblages in a Series of Different Types of Aquatic and Terrestrial Habitats of Wetland and Forest Ecosystems". Biology Bulletin. 50: 1719–1737. doi:10.1134/S1062359023080332.
^Gomaa, Fatma; Kosakyan, Anush; Heger, Thierry J.; Corsaro, Daniele; Mitchell, Edward A.D.; Lara, Enrique (2014). "One Alga to Rule them All: Unrelated Mixotrophic Testate Amoebae (Amoebozoa, Rhizaria and Stramenopiles) Share the Same Symbiont (Trebouxiophyceae)". Protist. 165 (2): 161–176. doi:10.1016/j.protis.2014.01.002.
^Jung W (1942). "Illustrierte Thekamöben-Bestimmungstabellen I. Die Systematik der Nebelinen" [Illustrated identification tables of thecate amoebae I. The systematics of the nebelines]. Archiv für Protistenkunde (in German). 95: 357–390.