foraminiferan


foraminiferan

      any unicellular organism of the rhizopodan order Foraminiferida (formerly Foraminifera), characterized by long, fine pseudopodia that extend from a uninucleated or multinucleated cytoplasmic body encased within a test, or shell. Depending on the species, the test ranges in size from minute to more than 5 cm (2 inches) in diameter and varies in shape, number of chambers, chemical composition, and surface orientation. Tests of a South Pacific species are large enough to be used as jewelry by oceanic islanders; nummulite specimens from the Eocene limestones of the Egyptian pyramids often exceed 5 cm in diameter. Foraminiferans inhabit virtually all marine waters and are found at almost all depths, wherever there is protection and suitable food (microscopic organisms).

      An important constituent of the present-day planktonic (floating) and benthic (bottom dwelling) microfaunas, foraminiferans have an extensive fossil record that makes them useful as index fossils (index fossil) in geological dating and in petroleum exploration. The word foraminiferan does not refer to the external pores found in some species but to the foramina (openings or apertures) between adjacent chambers after a new chamber envelops a previous one. When the foraminiferans die, their empty calcareous tests sink and form the so-called foraminiferal ooze that covers about 30 percent of the ocean floor. Limestone and chalk are products of the foraminiferan bottom deposits.

      The major factors governing the growth, reproduction, and distribution of foraminiferans are water temperature, depth, and salinity; availability of suitable food; nature of the substratum; and oxygen supply. The present-day foraminiferan population of the seas consists of six recognizably different faunas; four occur in warmer waters, two in colder waters.

      Although some species of foraminiferans reproduce exclusively by asexual means (multiple fission, budding, fragmentation), for most species there is a regular or an occasional sexual generation. Reproduction usually occupies one to three days, depending on the size and complexity of the species. Small species may complete both the sexual and asexual generations within a month, but larger species often require a year or two. Reproduction normally terminates the life of the parent, since all its cytoplasm is generally devoted to formation of the young.

* * *


Universalium. 2010.

Look at other dictionaries:

  • foraminiferan — noun Date: 1920 foraminifer …   New Collegiate Dictionary

  • foraminiferan — noun foraminifer …   Wiktionary

  • foraminiferan — fo·ram·i·nif·er·an …   English syllables

  • foraminiferan — fo•ram•i•nif•er•an [[t]fəˌræm əˈnɪf ər ən[/t]] n. pl. er•a [[t] ər ə[/t]] mcr foraminifer …   From formal English to slang

  • foraminiferan — var. of FORAMINIFER. * * * I. rən adjective Etymology: New Latin Foraminifera + English al : foraminiferal II. noun ( s) : one of the Foraminifera …   Useful english dictionary

  • Amoeboid — Foraminiferan (Ammonia tepida) Amoeboids are single celled life forms characterized by an irregular shape.[1] Amoeboid and amœba are often used interchangeably even by biologists,[2] and especially …   Wikipedia

  • Cretaceous Period — Interval of geologic time from с 144 to 65 million years ago. During the Cretaceous the climate was warmer than today. In the seas, marine invertebrates flourished, and bony fishes evolved. On land, flowering plants arose, and insects, bees in… …   Universalium

  • protozoan — /proh teuh zoh euhn/, n., pl. protozoans, (esp. collectively) protozoa / zoh euh/, adj. Biol. n. 1. any of a diverse group of eukaryotes, of the kingdom Protista, that are primarily unicellular, existing singly or aggregating into colonies, are… …   Universalium

  • Tertiary Period — Interval of geologic time, 65–1. 8 million years ago. It constitutes the first of the two periods of the Cenozoic Era, the second being the Quaternary. The Tertiary has five subdivisions: (from oldest to youngest) the Paleocene, Eocene, Oligocene …   Universalium

  • quaternary — /kwot euhr ner ee, kweuh terr neuh ree/, adj., n., pl. quaternaries. adj. 1. consisting of four. 2. arranged in fours. 3. (cap.) Geol. noting or pertaining to the present period of earth history, forming the latter part of the Cenozoic Era,… …   Universalium


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.