- Slides: 22
Lecture 5 Arrangement of chambers (Cont. )
q. Milioline: Winding growth with two chambers to the whorl with the aperture alternately at one end and then at the other. The successive chambers are added at 144º to each other (quinqueloculine), 120º (triloculine) or 180º (biloculine). Spiroloculina Pyrgo Quinqueloculina Triloculina
q. Polymorphine: The successive chambers spiral about the growth axis of the test, all the apertures pointing in the same direction. Guttulina Globulina gibba Polymorphina
q. Mixed chamber arrangement: Mixed or multiform growth, where the juvenile is different in arrangement from the adult chambers, is common and in some cases three different modes may be shown. -Planispiral to uncoiled uniserial, Astacolus. -Planispiral to biserial, Spiroplectammina. -Biserial to uniserial, Bigenerina. -Trochospiral to triserial, Eggerella.
-Triserial to biserial, Gaudryina. -Triserial to uniserial, Clavulina. -Trochospiral to annular conical, Patellina. -Planispiral to annular discoid, Archians. -Trochospiral or planispiral to annular complex, Orbitoides.
Morphology of chambers and the aperture • Chambers are spherical to flattened in shape. • They are separated from each other by partitions (or septa) the suture of which are rectilinear, curved or winding. • The last chamber communicates with the exterior through an aperture. • The aperture may be simple, in this case taking the shape of a circle, a slit or a crescent; or it may be radial or denderitic, sometimes at the top of a neck or partially covered by calcareous projections (tooth, valve, trematophore or tegillum). • There may also be multiple apertures with several small orifices arranged in a raw (linear aperture) or randomly (cribrate aperture). Its position in relation to the chamber may be basal, terminal, sutural or peripheral.
Diagrammatic illustration of tests bearing chambers of similar volume but with different growth coordinates
q. The shape of the aperture may be: ØRounded ØFissurine (elliptical) ØToothed (simple or bifid) ØStraight slit ØArched slit ØDenderitic ØPhialine ØRadiate ØCribrate
q. The position of the aperture may be: ØTerminal ØSubterminal ØSutural (textularian) ØAreal ØUmbilical ØInteriomarginal ØExteriomarginal ØEquatorial ØOn the apertural face ØAt the end of the tube q. Some modifications of the aperture: ØSimple lip ØCrenulated lips ØLateral flanges ØApertural teeth
Diagrammatic trochospiral tests with different kinds of aperture: ap. = aperture.
Surface ornamentation, • The surface of the test: is it smooth or covered with striations, ribs, tubercules, spines, etc. • The extranal surface of the test may bear spines (termed spinose), keels (carinate), rugae (rugose), fine striae (striate), coarse costae (costate), granules (granulate), or a reticulate sculpture. • These features should be used with caution in distinguishing certain genera and species for they vary through ontogeny and with environment.
The surface ornamentation of the test may be: -Costae, Ribs, striations. -Hispid (very fine short and hair-like spines). -Spinose (provided with very fine spines, generally elongate). -Rugose (characterized by rough ornamentation which may form ridges). -Nodose (surface ornamented with small knobs). -Reticulate (with a honey-comb like surface). -Beaded (provided with ornamentation like a string of beads). -Pitted (small, generally rounded depressions in the surface of the wal. -Limbated (bordered by or provided with a flat or raised strip). -Keeled (marginal cord of the periphery). -Carinae (the edges of the chambers often bear projecting sharp keels). -Septal bridges (retral processes). -Smooth.
Sutures They are simple or limbate (underlined by a band of variable width). The sutures are of two types: -Spiral suture; division between different whorls of the test. -Intercameral suture; division between the chambers themselves. It may be described as: Depressed, Flush, raised, limbate and obscured by the cortex. Or may be : Straight, arched or curved, grooved and reticulate.
Periphery of the test: is the outer margin of the test, termed as the axial periphery (as shown in the axial or periphery view) and the equatorial periphery (as shown in ventral or dorsal view). The axial periphery may be desribed as: ØRounded ØAcute ØKeeled (ridge-like thickening of the chamber wall, present on the periphery of the test. The equatorial periphery may be described as: ØLobulate ØNonlobulate
Umbilicus: is it vacant or occupied by one or more granules. It is a central area where the septal traces (sutures) meet. When the umbilicus is completely filled with secondary material, it is called umbo. If slightly filled, it is called an umbilical plug. The test may be described as: Umbilicate test (with an umbilicus). -Monoumbilicate as in Globigerina -Biumbilicate as in Hantkenina and Hastigerina. Umbonate test (with an umbo) Monoumbonate as in Rotalia =Streblus=Ammonia Biumbonate as in Robolus & Elphidium