Xenophyophorea
Xenophyophorea /ˌzɛnəˌfaɪəˈfoʊriːə/ is a clade of foraminiferans. Members of this class are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of 500 to 10,600 metres (1,600 to 34,800 ft).[3][4] They are a kind of foraminiferan that extracts minerals from their surroundings and uses them to form an exoskeleton known as a test.
They were first described by Henry Bowman Brady in 1883. They are abundant on abyssal plains, and in some regions are the dominant species. Fifteen genera and 75 species have been described, varying widely in size.[5] The largest, Syringammina fragilissima, is among the largest known coenocytes, reaching up to 20 centimetres (8 in) in diameter.[6]
The name Xenophyophora means "bearer of foreign bodies", from the Greek. This refers to the sediments, called xenophyae, which are cemented together to construct their tests. In 1883, Henry Bowman Brady classified them as primitive Foraminifera.[7] Later they were placed within the sponges.[8] In the beginning of the 20th century they were considered an independent class of Rhizopoda,[9] and later as a new eukaryotic phylum of Protista.[10] As of 2015, recent phylogenetic studies suggest that xenophyophores are a specialized group of monothalamous (single-chambered) Foraminifera.[11][12][13]
A 2013 molecular study using small subunit rDNA found Syringammina and Shinkaiya to form a monophyletic clade closely related to Rhizammina algaeformis.[14] Further molecular evidence has confirmed the monophyly of xenophyophores. This study also suggested that many individual genera are polyphyletic, with similar body shapes convergently evolving multiple times.[15]
Historically xenophyophores have been divided into the agglutinated psamminida and the flexible, proteinaceous stannomida.[16] However, cladistic analyses based on molecular data have suggested a high amount of homoplasy, and that the division between psamminids and stannomids is not well supported.[15]
Xenophyophores /ˌzɛnəˈfaɪəfɔːrz/ are unicellular, but have many nuclei. Many form delicate and elaborate agglutinated tests—shells often made of calcium carbonate (CaCO3) and other foreign mineral particles glued together with organic cements[17]—that range from a few millimetres to 20 centimetres across. The softness and structure of tests varies from soft and lumpy shapes to fans and complex structures.
