B. van Niel: Scanning electron micrographs .. , p. 7'5 - 77.

\Journal ofNannoplankton Research, 16, 2, 1994.

SCANNING ELECTRON MICROGRAPHS OF THE GENUS KOKIA(INCERTAE SEDIS)
Brigitta van Nie/, Institute of Oceanographic Sciences, Brook Road, Wormley, Surrey. GU8 5UB
Introduction
Kokia is a genus of flat, rosette shaped Early Cretaceous(Ryazanian to Hauterivian) nannoliths. Specimens weredescribed by Kok ( 1985), as UFO 2, and subsequently by
Perch-Nielsen (1988), who formally described the genus
Kokia including two new species, K. borealis, and K.
curvata.
During examination of Ryazanian (Berriasian)North Sea sediments Kokia was found to be common andthe opportunity was taken to examine it in the LM andSEM using the technique developed by Gallagher ( 1988).
This genus has previously only been illustrated in crosspolarised light (Kok, 1985, PI. I figs 11-13 andPerch-Nielsen, 1988, PI. 1, figs 8-14). This short note
illustrates Kokia spp. from NW Europe in the LM andSEM showing detail of the construction of the plates.
Tentative affinities for this genus are discussed.
Observations
Kok (1985, p. 38) noted the presence of " a narrow axialdepression" in specimens of Kokia . In the genericdiagnosis, Perch-Nielsen ( 1988, p. 31) stated that '' there
is no central hole" . Observation on the central part ofK. borealis implies that there is a small central opening
which appears to be covered by a thin diaphragm ofcalcite
which can easily be damaged (PI. 1, figs 1c-e). This feature
may give the appearance of no central hole in the LM.
Most specimens observed had 8 rays althoughsome specimens were constructed of 10 rays (PI. I, fig. 5).
In the LM two apparently superimposed specimens weresometimes observed, however, no similar structures werefound in the SEM, possibly due to the fragile nature of thestructure. In the SEM the specimens are clearly shown to
be rather flat and about l~m thick (PI. l, fig. 2c).
When specimens are observed in crossed polars theindividual rays show straight extinction. Use of a gypsum
plate (cf. Moshkovitz & Osmond, 1989; Young, 1992)
shows that this is due to them having tangential
crystallographic orientation, in contrast to the radial
orientation observed in most coccoliths.
The rays appear to be constructed of a single plate
giving a smooth appearance, with the free part of the rays
being short or elongate, truncated or· pointed. J.solated
paired rays show some similarities to broken segmentsfrom Micrantholithus (PI. 1, fig. 3). However, in the LM
each ray can be clearly observed in Kokia specimens
whereas in Micrantholi thus specimens the segments form
a complete unit. A second cycle of very thin plates can beobserved around the central opening (PI. 1, figs le & d).
It is uncertain whether these plates form a thin diaphragmaround the central area.
Possible Affinities
The biological affinity of this genus has been tentatively
assigned to Ascidian spicules, in particular to the family

Didemnidae, by Varol & Girgis ( 1994, in press) and Varol& Houghton (in prep). The taxon, K. borealis, previously
only observed in the LM, was inferred to resemble theSEM illustration of Lissoc/inum argyllense in Monniot(1970, PI. 2). The SEM micrographs illustrated in thispaper clearly illustrate dissimilarities between the threedimensional Ascidian spicules and the flat genus Kokia .
Moreover, ascidian spicules show radial crystallographic
orientations.
Structurally the specimens appear similar to thecalcareous pentalith genera of the Braarudosphaeraceae.
These genera are constructed of flat pentaliths of variable
shape, sometimes with a central opening. In some genera
e.g. Pen/aster the segments may bear rays. Moshkovitz( 1987, p. 1120) observed that in proximal view, Bulayasterhayi has a very thin calcitic layer beneath which lies a starshaped body. This construction appears similar to thatobserved in plate 1, figs le & d). However, the large
number of rays in the genus Kokia means it must still beconsidered 'incerlae sedis '.The tangential crystallographic
orientation of the rays would support affinities with either
the Braarudosphaeraceae or the Polycyclolithaceae, bothof which characteristically have tangential c axes
(Moshkovitz & Osmond, 1989).
Taxonomic Combinations
Kokia borea/is Perch-Nielsen (1987)
Kokia curvata Perch-Nielsen (1987)
REFERENCES
Gallagher, L.T., 1988: A technique for viewing the samenannofossil specimen in light microscope and scanningelectron microscope using standard preparationmaterials. J. Micropalaeontol., 7, 53-57.
Kok, C.P., 1985: UFO 2. An Early Cretaceous nannofossil fromthe Central North Sea. INA News/. 7, 38.
Monniot, F., 1970: Les spicules chez les Tuniciers
Aplojusobranches. Archs. zoo/. exp. gen .. 111 , 303312.
Moshkovitz, S. 1987: The Campanian calcareous nannofossil
Bukryaster hayi (Bukry): Ultrarnicrostructure and geological distribution in Israel. J. Paleont., 61 , 1120-1124.
Moshkovitz, S. & Osmond, K., 1989: The optical properties andmicrocrystallography ofArkhangelskiellaceae and someother calcareous nannofossils in the Late Cretaceous. In," Nannofossils and their Applications" , ( eds Crux J. &Heck S.E. van), 76-97. Ellis Horwood, Chichester.
Perch-Nielsen, K. , 1988: New Lower Cretaceous calcareous
nannofossil species from England. INA Newsletter., 10,30-36.
Varol, 0 . & Girgis, M., In press: New taxa and taxonomy ofsome Jurassic to Cretaceous calcareous nannofossils.
Ns. Jb. Geol. Palliont. Abh., 192, 153-185.
Varol, 0 . & Houghton, S., In prep.: A review ;md classificationof fossil didemnid ascidian spicules from fme-grained
sedirnents. Submitted to J. Micropalaeontol.
Young, J. R., 1992. The description and analysis· of coccolith
structure. Knihovnicka ZPN., 14a, 35-71.

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B. van Niel: Scanning electron micrographs .. , p. 75 - 77.

PLATE 1
1-4:

1a:
lb:

le:
ld:

2a:
2b:
2c:
Ja:
4 a:
4 b:
4 c:
5:

Kokia. borealis. Upper Ryazanian. Danish Central Trough, North Jens-1 , 7950 m. Figs 1 a-d, 2 a-c and
4 a- c are same specimen photographs.
Cross-polarised light.
Scanning electron microscope.
Detail of the central area and base of ray.
Detail of the central pore which appears to be covered by a thin, damaged diaphragm.
Cross-polarised light.
Scanning electron microscope.
Oblique view illustrating the thin, flat nature of this genus.
Pair of broken rays.
Cross-polarised light.
Scanning electron microscope.
Detail of the central pore and diaphragm.
Kokia sp. A 10-rayed specimen. Overgrowth of the specimen has obscured some of the structural detail. UpperRyazanian. Danish Central Trough, North Jens-1 , 7950 m.

Horizontal scale bars: 10 Jlm for the light micrographs (shown in fig. 4a) and 1 Jlm for all scanning electron micrographs .

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B. van Niel: Scanning electron micrographs.., p. 7S - 77.

Journal ofNannoplanklon Research, 16, 2, 1994.

1a2a1b2b1C2c4C

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