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Nannoconids

The Nannoconaceae are a monogeneric group of rock-forming Late Jurassic - Late Cretaceous, nannoliths of uncertain affinities. The terminology applicable to Nannoconus is reviewed in detail by van Niel (1994), and the following is a list of key terms only.
Informal taxon-based term: nannoconid.

1. Associations

Groups of associated nannoconid individuals have been found by various workers: Trejo (1960); Colom (1965); Ozkan (pers. comm.). These associations have only a very small common opening and may represent colonial groups of cells (cf. many diatoms) rather than single organisms (cf. typical coccospheres).
Association a group of systematically arranged individuals. {van Niel, 1994}
Rosette association of nannoconids lying side-by-side with their longitudinal-axes radiating from a central point. N.B. It is possible that all rosettes are spherical, but the term sphere is not recommended since this has not been demonstrated, and since nannoconid associations may not be strictly comparable to coccospheres. {Noel 1958}
Twin two nannoconid individuals joined at their ends, with ridges and grooves extending across the contact surface. {van Niel 1995}

2. Orientation

Longitudinal axis axis of rotational symmetry of nannoconid.
Transverse plane plane perpendicular to the longitudinal axis.
Horizontal directions within the transverse plane.
Vertical directions parallel to the longitudinal axis.
Pole end of nannoconid, point of emergence of symmetry axis:
apex pole in N. steinmannii at narrower end of specimen {Bronnimann 1955};
base - pole opposite to apex (broader end in N. steinmannii).{Bronnimann 1955}
Longitudinal view view of nannoconid parallel to longitudinal axis.
Plan view view of nannoconid perpendicular to longitudinal axis.

3. General terms

Central opening opening running longitudinally through the nannoconid. Types:
canal - narrow, <1 µm;
cavity - wide, >1 µm;
aperture - expression of the central opening at the ends of the specimen. {Kamptner 1931}
Bulb a distinct swelling of the outline (e.g. N. borealis - single, N. paskentiensis - double, N. multicadus - triple). {Trejo 1960}
Constriction external indentation of the wall, between bulbs. {Deflandre and Deflandre-Rigaud 1962}
Flange horizontal projection around the end of nannoconid. N.B. Flanges may be symmetrical or asymmetrical in end view, and may be present at one or both ends of the specimen. {Stradner and Grün 1973}
Wall structure enclosing the central opening. {Kamptner 1931}

nannoconid terms

4. Structure

Nannoconids appear to be formed of two types of plates arranged in alternating cycles (van Niel 1992). These cycles appear to spiral around the wall but the precise geometry is not yet clear.
Plate basic structural element of nannoconid, single sub-triangular platy crystal. (Alternative term wedge, see appendix). {Stradner and Grun 1973}
Type A-cycle cycle of plates inclined at a lower angle (angle α) to the horizontal. These are birefringent in longitudinal view (Perch-Nielsen 1988). {van Niel 1992}
Type B-cycle cycle of plates inclined at a higher angle (angle β) to the horizontal. These cycles are non-birefringent in longitudinal view and form the dark spiral lines observed in cross-polars in longitudinal view (Kamptner 1931, Deflandre and Deflandre-Rigaud 1962, Perch-Nielsen 1988). {van Niel 1992}
Angle Δ angle of the A cycle/B cycle contact to the horizontal. N.B. This is the only angle measurable by light microscopy. {van Niel 1992}
Cycle spacing repeat distance between cycles perpendicular to angle Δ, i.e. combined thickness of A and B cycles.
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