Instituted of Geology

6th Semester (Morning)

Submitted by: Khawar-u-zaman babar

Roll No: 53

Submitted To: Dr.Munir

Subject: Micropaleontology

Topic

MORPHOLOGICAL FEATURES OF FORAMINIFERA

Morphological feature of foraminifera

Kingdom: Protista

Subkingdom: Protozoa

Phylum: Sarcomastigophora

Subphylum: Sarcodina

Super class: Rhizopoda

Class: Granuloreticulosea

Order: Foraminiferida (foraminifera).

Introduction:The order foraminiferida or foraminifera as they are informally called forms the most important group of

microfossils fortwo reasons: first, they are abundant in rocks and there arenumerous species; second they provide valuable information in thedating of strata and the reconstruction of sedimentary environments.Foraminifera are an order of single-celled protests that liveeither on the sea floor or amongst the marine plankton. The softtissue (protoplasm) of the foraminiferid cell is largely enclosed withina shell (test) variously composed of secreted minerals (calcite,aragonite or silica) or of agglutinated particles. This test consists of asingle chamer or several chambers mostly less than 1 mm across and each interconnected by an opening

(foramen) or several openings(foramina). Foraminifera are known from early Cambrian timesthrough to recent times.Foraminifera are found in all marine environments, they may beplanktic or benthic in mode of life. The generally acceptedclassification of the foraminifera is based on that of Loeblich andTappan (1964). Unpicking this nomenclature tells us thatforaminifera are testate (that is possessing a shell), protozoa, (singlecelled organisms characterised by the absence of tissues and organs),which possess granuloreticulose pseudopodia (these are thread-likeextensions of the ectoplasm often including grains or tiny particles ofvarious materials).

Life Cycle:

Classification

Foraminifera are classified primarily on the compositionand morphology of the test. Three basic wall compositions arerecognised, organic (protinaceous mucopolysaccharide i.e. the

allogromina), agglutinated and secreted calcium carbonate (or morerarely silica). Agglutinated forms, i.e the Textulariina, may be

composed of randomly accumulated grains or grains selected on thebasis of specific gravity, shape or size; some forms arrange particular

grains in specific parts of the test. Secreted test foraminifera areagain subdivided into three major groups, microgranular (i.e.

Fusulinina), porcelaneous (i.e. Miliolina) and hyaline (i.e.Globigerinina). Microgranular walled forms (commonly found in the

late Palaeozoic) are composed of equidimensional subspherical grainsof crystalline calcite. Porcelaneous forms have a wall composed of

thin inner and outer veneers enclosing a thick middle layer of crystallaths, they are imperforate and made from high magnesium calcite.

Test Morphology:Foraminifera are animals which build a shell; and for paleontologiststhe characterstics of the shell are the primary features which can be

used to distinguish one species from another.Wall Structure:

The most readily obvious featuredistingushing one foraminifer fromanother is its wall type. Whether the foraminifer builds its test wall

by cementing together exogenous grains, by carbonatemineralization, or by some combination of these two processes

separates the three primary foraminiferal groups, the agglutinated,the calcareous, and the microgranular foraminifera.

Agglutinated wall structureIn these, organic and mineral matter from the sea floor is bound

together by an organic, calcareous or ferric oxide cement. The grainsare commonly selected for size, texture or composition (e.g.

coccoliths, sponge, spicules and heavy minerals). Other agglutinatedforms are non-selective and will employ any particle from a substrate

as long as it lies in the appropriate size range.

Microgranular wallsMicrogranular walls evolved during the Paleozoic and are

consideredthe link between the agglutinated and the precipitated tests inforaminifera. Microgranular particles of calcite cemented by a

calcareous cement characterize this wall type and give it a sugary

appearance.Calcareous walls- hyaline type

Calcareous wall may be composed of either low or high Mg calcite, or

aragonite which is confined to only two foraminiferal families.Hyaline calcareous tests are characterized by the possession ofminute perforation in the test wall. The calcareous hyaline aregenerally glassy (hyaline) when viewed with reflected light and

greyto clear in transmitted light.

Chamber shape and chamber arrangement

:Foraminiferal tests may posses one or more chambers. The

initial chamber is most often spherical or oblate with an aperture.Later chambers range in shape from tubular, spherical, ovate to

several others. Additional chambers are added in a variety ofpatterns termed chamber arrangements:

1- Uniserial: the chamber arranged in a single row; if it forms acurved row, it is termed arcute; if a straight series, it is termed

rectilinear.2- Biserial: the chambers arranged in a double row.

3- Triserial: Chambers are added every 120o in a spiral fashion.4- Polyserial: the chambers arranged in a multiple row.

5- Planispiral: the chamber arranged spirally around an axis ofcoiling and the spiral lies in a single plane.

• 6- Trochospiral: when the spiral does not lie in one plane, but

• progresses up up the axis of coiling, the chamber arrangement

• becomes helicoidal.• 7- The Miliolidae have a streptospiral arrangement.

The arched• chambers, tangential at their two extremities with

the extension axis,• are arranged in cycles of five, three or two loculi or

one loculus. Each• new chamber has its aperture facing the aperture

of the the• preceding chamber.• When

Apertures and openings:The aperture is the primary opening of the test to the outsideenvironment. Apertures vary in size and shape and the shape is mostoften a function of the shape of the chamber on which they arelocated. The aperture is found in the wall of the final chamber andserves to connect the external pseudopodia with the internalendoplasm, allowing passage of food and contractile vacuoles, nucleiand release of the dauther cells.Aperture may be single or multible in number and terminal, areal,basal extraumbilical, umbilical or sutural in position. Their shapevaries widely, e.g. rounded, bottle-necked (phialine), radiate,dendritic, sieve-like (cribrate), circular form, slit- or loop- shaped.