''Sigmoilina'' is a miliolid genus, referring to the foraminiferal order Miliolida, characterized by an assymmetricall biconvex test formed by strongly overlapping chambers, one-half coil in length, that form a sigmoid (S-shaped) curve in cross section. The strongly overlapping chambers obliterate earlier ones from view resulting in the compressed biloculine appearance, differing from the squat, depressed biloculine form of '' Pyrgo'' and '' Biloculina''. The test, as for all Miliolida, is porcelaneous and imperphorate, the terminal aperture, with tooth, the only point of egress and ingress for the animal. ''Sigmoilina'' is a

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the e ...

, or proctoctist according to B.K. Sen Gupta, 1999, included in the miliolid family

Hauerinidae Hauerinidae is a large and diverse family of miliolid forams ( Loeblich & Tappan, 1988) that includes genera distributed among various subfamilies in the Treatise (Loelich &Tappan 1964) as well as genera named and described since. Diagnosis T ...

( Loeblich & Tappan, 1988). It was previously assigned to the

Miliolidae ''Miliolidae'' is a family in the superfamily ''Miliolacea'' of miliolid foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists charact ...

(Loeblich & Tappan, 1964) when foraminifera were regarded as comprising a suborder (Foraminiferida).

References

* Alfred R. Loeblich Jr and Helen Tappan, 1964. Sarcodina Chiefly "Thecamoebians" and Foraminiferida; Treatise on Invertebrate Paleontology, Part C Protista 2. Geological Society of America and University of Kansas Press. * Alfred R. Loeblich Jr and Helen Tappan, 1988
Forminiferal Genera and their Classification.
*Barun K. Sen Gupta 1999
Modern Foraminifera.

''Sigmoilina''
in Fossilworks (Paleo db) {{Taxonbar, from=Q20720306 Tubothalamea Foraminifera genera Extant Miocene first appearances