Xenophyophorea is a clade of foraminiferans. Xenophyophores are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of 500 to 10,600 metres. They are a kind of foraminiferan that extract minerals from their surroundings and use them to form an exoskeleton known as a test.
Image: Xenophyophore NOAA
Image: Xenophyophore
A large 20-cm wide xenophyophore
Paleodictyon has been suggested as a fossil xenophyophore, but this remains controversial.
Foraminifera are single-celled organisms, members of a phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an external shell of diverse forms and materials. Tests of chitin are believed to be the most primitive type. Most foraminifera are marine, the majority of which live on or within the seafloor sediment, while a smaller number float in the water column at various depths, which belong to the suborder Globigerinina. Fewer are known from freshwater or brackish conditions, and some very few (nonaquatic) soil species have been identified through molecular analysis of small subunit ribosomal DNA.
Foraminifera
Fossil nummulitid foraminiferans showing microspheric (larger) and megalospheric individuals (smaller); Eocene of the United Arab Emirates; scale in mm
Foraminiferan tests (ventral view)
The mysterious Paleodictyon has been interpreted as a fossil xenophyophore but this remains controversial.