Subembryonic 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)


  • according to Hottinger (2006):

SUBEMBRYONIC CHAMBERLETS - chamberlets that are produced in a mono- or plurilocular third stage in the growth of megalospheric embryos of agglutinated conical foraminifera. They are located below the proloculus in the cone axis and are subdivided by structural elements of uncertain, probably exoskeletal origin.

Remarks: J. Hofker Jr (1963, p. 211, fig. 14) interpreted the life habit of an orbitolinid as face upward, i.e. the cone apex downward, buried in the sediment. Therefore, he called the third growth-stage in Orbitolina s.str. "epiembryonic". The confusion up-down is complicated by a supposed error in the legend of fig. 2 in J. Hofker Jr (1966), where deuteroconch and epiembryonic chambers are reversed by comparison with his 1963 paper. Today, all foraminifera with an extensive apertural face covered by numerous apertures live with their apertural face towards the substrate. Undoubtedly, the same is true for conical foraminifera in general. The term epiembryonic is therefore to be avoided. Douglas (1960) did not distinguish between sub- and periembryonic chambers, both representing the third growth stage.

See also


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.

Hofker (1966), Studies on the family Orbitolinae, Palaeontographica, Stuttgart, (Abteilung A), Band 126, Lieferung 1-2, p. 1-34 + 10 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.

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