Involutinida is an order of
foraminifera
Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular Ectoplasm (cell biology), ectoplasm for catching food and ot ...
included in the
Spirillinata found in the fossil record from the early
Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
to early
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
(
Cenomanian
The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...
).
Diagnosis
The Involutinida are characterized by a two chambered
aragonitic
Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...
test
Test(s), testing, or TEST may refer to:
* Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities
Arts and entertainment
* ''Test'' (2013 film), an American film
* ''Test'' (2014 film), ...
consisting of an initial spheroidal chamber, or proloculus, enclosed by a tubular second, or main chamber. The test wall may be bilamellar (two layered), the inner layer being microgranular and often dark, the outer hyaline (ckear, glassy). Coiling may be planispiral or trochospiral, forming a cone. Lamellar thickenings or pillar-like structures may be found in the umbilical region on one ore both sides.
[ Alfred R. Loeblich Jr & Helen Tappan,1988. Forminiferal Genera and their Classification. Van Nostrand Reinhold.]
Taxonomy
Four families are included in Involutinida,
[ three of which, the Involutinidae, Hirsutospirellidae, and Planispirillinidae all have undivided tubular second chambers. The fourth, the Ventrolaminidae has numerous chambers following the proloculus. All four are represented by planispiral or trochospiral forms.
]
History
The concept of the Involutinida has developed over the years, beginning with the Involutinidae as described in the ''Treatise'' Part C, 1964,
References
Foraminifera orders
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