Periembryonic chamberlets

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Fig. 1. Embryonic apparatus. A: Discocyclina, stereograph after Ferràndez (1999), modified. Schema, not to scale. B: Discocyclina sp., equatorial section, showing corona. Transmitted light micrograph. C: Amphisorus sp. Stereograph, schema, not to scale. D: Amphisorus hemprichii Ehrenberg from the Gulf of Aqaba, Red Sea. Recent. Equatorial section, transmitted light micrograph, showing flexostyle and forecourt. E: Orbitolites sp., stereograph after Lehmann, 1961, redrawn. Note the shape like a dumb-bell of the proloculus. F-G: Orbitolites sp., Lower Eocene, Pakistan, Allemann collection. Oblique-centered sections, in approximately equatorial and axial direction, showing flexostyle constricting the proloculus. Transmitted light micrographs. H: Orbitopsella sp., stereograph showing sphaeroconch with its exoskeleton. Schema, not to scale, after Hottinger, 1967. Note the appearance of endoskeletal pillars not before the third chamber. I: Orbitopsella praecursor (Gümbel), Middle Lias, Morocco, equatorial section showing the thin proloculus wall and the sphaeroconch with its simple exoskeleton consisting of beams only. Transmitted light micrograph. J: Advanced orbitoliniform embryo, schematic, not to scale. Note the apex that is directed downwards (arrows) to facilitate the comparison with Hofker's drawings (1963). K-L: embryos of Karsella hottingeri Sirel, a Upper Paleocene form that exhibits an architecture strikingly similar to the one of Mid-Cretaceous orbitolinids. Pakistan, Allemann collection. Transmitted light micrographs. M: Sabaudia minuta Hofker Jr, embryo followed by three agglutinated chambers of the same series and presenting a simple exoskeleton. Lower Cretaceous. Note the hyaline embryo wall. The embryos are known to be formed within the mother shell and seem to have no access to grains in the environment to build their agglutinated walls. achl: auxilliary chamberlet; ap: annular passage; ast: annular stolon; b: beam; d: deuteroconch; ecr: equatorial crest; fl: flexostyle; il: inner lamella; lchl: lateral chamberlet; mchl: main chamberlets; ol: outer lamella: ost: oblique stolon; ost(d): oblique stolon of deuteroconch; p: pore; pap: papilla; peri: periembryonal chamberlets; pi: pillar; pr: proloculus; rst: radial stolon; rst(d): radial stolon of deuteroconch; s: septum; sc: sphaeroconch; sl: septulum; sub: subembryonic chamber (=deuteroconch); supra: supraembryonic chamber; (Hottinger, 2006; fig. 41 [1] CC/BY-NC-SA)


Definition

  • according to Hottinger (2006):

PERIEMBRYONIC CHAMBERLETS - corona (periembryonic cells); all chamberlets in contact with an embryonic apparatus. In orbitoidiform architecture the term is restricted to the chamberlets of the equatorial main layer and is a synonym of "corona". In orbitolinids the periembryonic chamberlets designate the forth stage of growth consisting of an annular chamber subdivided into chamberlets. The fifth chamber may be called nepionic, and is annular or discoidal, radially subdivided by septula following the constraints of crosswise-oblique stolon axes disposed in radial rows.


Remarks: Introduced by Douglas (1960), the term periembryonic originally included subembryonic chambers, without analyzing in detail the complicated structures of this part of the test. Today, much weight is given to the distinction between periembryonic and subembryonic chambers (Schröder, 1962; Arnaud-Vanneau, 1980).

See also

References

Arnaud-Vanneau (1980), Micropaléontologie, paleoécologie et sédimentologie d'une plate-forme carbonatée de la marge passive de la Téthys: l’Urgonien du Vercors septentrional et de la Chartreuse (Alpes occidentales), Géologie Alpine, Grenoble, Mémoire 11, 3 vols., 876 p. + 115 pls.

Douglas (1960), The foraminiferal genus Orbitolina in North America, Geological Survey Professional Paper, Washington, 333, 52 p. + 14 pls.

Ferràndez I Cañadell (1999), Morfoestructura i paleobiologia dels Ortofragmínidos de la Mesogea (Discocyclinidae i Orbitocyclinidae, Foraminifera), Arxius de les Seccions de Ciències, Barcelona, (Secció de Ciències i Tecnologia), CXXI, 339 p.

Hofker (1963), Studies on the genus Orbitolina (Foraminiferida), Leidse Geologische Mededelingen, Leiden, vol. 29, p. 181–253 + 23 pls.

Hottinger (1967), Foraminifères imperforés du Mésozoïque marocain, Notes et Mémoires du Service géologique, Rabat, N° 209, p. 5-168

Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744

Lehmann (1961), Strukturanalyse einiger Gattungen der Subfamilie Orbitolitinae, Eclogae geologicae Helvetiae, Basel, vol. 54, N° 2, p. 597-667.

Schröder (1962), Orbitolinen des Cenomans Südwesteuropas.- Paläontologische Zeitschrift, Stuttgart, Band 36, N° 3-4, p. 171-202.

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