MESOZOIC CALCAREOUS NANNOPLANKTON CLASSIFICATION

Remarks: A strictly morphological taxonomic grouping which embraces coccolithophores which secrete holococcoliths. Almost certainly includes taxa which also secrete heterococcoliths during non-motile phases and are then included in other families.

The list below is probably overdivided, particularly the small forms which have rims formed from numerous blocks and have only rarely been observed in the LM. However, a number of taxa are consistently recorded and applied in biostratigraphy, e.g. Anfractus, Calculites and Lucianorhabdus.

2a. Cavate, Anfractus-like holococcoliths

Anfractus holococcoliths have been recorded inconsistently from Early Jurassic to mid-Cretaceous sediments (see Bown, 1993; Lambert, 1987).
Anfractus Medd, 1979 emend. Bown, 1993 {elliptical, cavate (and usually septate), often bearing hollow spines; distal surface may be perforate; may have internal buttresses}
Stereorhabdus Lambert, 1987 {spine terminates in a stellate process}

2b. Cavate with three to four proximal blocks, Lucianorhabdus -like

These forms are large and robust, and have been recorded consistently from Late Cretaceous sediments. They are typically cavate but diagenesis commonly produces infilled cavities/spines and overgrown blocks.

Acuturris Wind & Wise in Wise & Wind, 1977 {proximal plate of 3 blocks; tall, tapering spine}
Calculites Prins & Sissingh in Sissingh, 1977 {proximal plate of 4 blocks; ridged and pitted distal surface; short, narrow, hollow spines}
Isocrystallithus Verbeek, 1976 (= Owenia Crux, 1992) {?cavate holococcoliths bearing moderately tall spines}
Lucianorhabdus Deflandre, 1959 {proximal plate of four blocks; tall, hollow spine, often ridged or pitted; may be bulbous or curved}
?Genus Orastrum Wind & Wise in Wise & Wind, 1977 {narrow rim surrounds central-area formed of 2-4 blocks; ?non-cavate, ?no spine}
[Owenia Crux, 1992] {bicyclic; narrow central-area spanned by arched bar. Junior synonym of Isocrystallithus}
[Semihololithus Perch-Nielsen, 1971] {the genus is probably a junior synonym of Daktylethra (Cenozoic). The Mesozoic species should probably be assigned to Calculites or Lucianorhabdus}

2c. Rim formed from numerous small blocks with variable central structures

These forms are small and, in most cases, have only been described in the LM from a limited number of sites/samples; mainly Late Cretaceous.

Bifidalithus Varol, 1991 {narrow rim with central-area filled by two blocks divided by a transverse suture}
Multipartis Risatti, 1973 {rim formed from ~7 triangular blocks; irregular blocks in the central-area}
Munarinus Risatti, 1973 {rim formed from 4-12 blocks; central-area filled or spanned by disjunct bar/block}
Octolithus Romein, 1979 {rim formed of 8 blocks, 4 large and 4 small}
Okkolithus Wind & Wise in Wise & Wind, 1977 {rim of ~20 blocks; central-area filled by 2 or more disjunct blocks}
Ottavianus Risatti, 1973 {rim of 10-15 blocks, central-area spanned by ?conjunct bar/block}
Pharus Wind & Wise in Wise & Wind, 1977 {elliptical, comprising one or two blocks, pierced by two round holes}
Ramsaya Risatti, 1973 {rim of 12-14 blocks, central-area spanned by a narrow, dark bar}
Russellia Risatti, 1973 {rim of 10-26 blocks; central perforation}
Saepiovirgata Varol, 1991 {rim of 8-12 elements, with 2 longitudinally-oriented elongate blocks in the central-area}

2d. Others with recognisable coccolith morphology

Coccosphaerida Lambert, 1987 {high rim, formed from 3 layers of crystallites, ?distal surface covering}
Lacunolithus Bown, 1993 {cavate, open proximal ring, flaring collar, domed distal covering}

2e. Non-coccolith morphology

[Athenagalea Hattner & Wise, 1980] {junior synonym of Petrobrasiella}
Metadoga Wind & Cepek, 1979 {conical-flask-shaped, with lid and internal partition}
Petrobrasiella Troelsen & Quadros, 1971 {domed-shaped, pierced by holes/cavities}
Pseudoconus Bown & Cooper, 1989 {solid, truncated-cone-shaped ?holococcolith with rectangular cross-section}
Zebrashapka Covington & Wise, 1987 {solid, truncated-cone-shaped ?holococcolith, with distinct outer rim and banded core}

3. NANNOLITHS

Comments: The groups included here are mostly extinct taxa which had calcite tests within the size limits of calcareous nannofossils but with morphologies which are distinct from either hetero- or holococcoliths.

Family BRAARUDOSPHAERACEAE Deflandre, 1947

Description: The extant species Braarudosphaera bigelowii has not been cultured but observations on live specimens suggest that it is a haptophyte (J. Green, pers. comm., 1996). It has a cell-wall covering of twelve pentaliths, which form an imperforate dodecahedron. The nannoliths are constructed from five segments which form a pentalith (a five-sided plate), although stellate outlines are also common. C-axes are tangential to pentalith outline in plan view and individual crystal units show laminar ultrastructure.

Braarudosphaera Deflandre, 1947 {elements trapezoidal, sutures go to edges of the pentagon}
?Bukryaster Prins, 1971 {stellate; sutures go to edges of the pentagon; ornament of 5 ridges and depressions}
Micrantholithus Deflandre in Deflandre & Fert, 1954 {sutures go to points of the pentagon; relationship between Neocomian and Cenozoic representatives uncertain}
Trapezopentus Wind & Cepek, 1979 {pentalith formed from 5 subrectangular elements surrounding a large central opening}

Family EOCONUSPHAERACEAE Kristan-Tollmann, 1988

Description: Nannoliths with a truncated-cone-like morphology constructed from an outer rim of thin, elements joined along vertical sutures, and an inner core of numerous radial lamellae which protrude distally.

Comments: The three genera listed below have non-concurrent stratigraphic ranges but very closely comparable morphologies and biogeographies (Bown & Cooper, 1989). The taxonomic validity of this grouping is thus uncertain. These forms may prove to be modified heterococcoliths.

Calcivascularis Wiegand, 1984 (= Mitrolithus jansae ) {inner core differentiated into proximal and distal parts, Early Jurassic}
Conusphaera Trejo, 1969 {inner core differentiated longitudinally into 2 concentric cycles, L. Jurassic-E. Cretaceous}
Eoconusphaera Jafar, 1983 {inner core formed from a single cycle of radial laths, Late Triassic}

Family GONIOLITHACEAE Deflandre, 1957

Description: Pentagonal plates with a thin rim and granular central-area plate.

Comments: Rare and sporadic stratigraphical distribution; K/T boundary survivor.

Goniolithus Deflandre, 1957 {pentagonal plate with a distinct rim surrounding a mesh-like array of small crystals}

Family LAPIDEACASSACEAE Bown & Young 1997

Type genus: Lapideacassis Black, 1971.

Description: Hemispherical to cylindrical nannoliths, with walls constructed from one to several cycles of thin elements, enclosing a hollow central space; the nannolith tapers ?distally, and may have ?apical spines or processes.

Comments: Rare and sporadic stratigraphic distribution, but K/T boundary survivor.

Lapideacassis Black, 1971 (= Scampanella Forchheimer & Stradner, 1973; Pervilithus Crux, 1981) {see family description}
[Scampanella Forchheimer & Stradner, 1973] {has been used for forms with a single wall cycle; regarded here as a junior synonym of Lapideacassis}

Family MICRORHABDULACEAE Deflandre, 1963

Description: Elongate, rod-like nannoliths with a cruciform or circular cross-section, which generally taper at both ends.

Comments: The relationship between the four genera listed below is uncertain and this family may prove to be polyphyletic.

Lithraphidites Deflandre, 1963 {narrow rods with cruciform cross-section; may have expanded lateral blades}
Microrhabdulus Deflandre, 1959 {~circular cross-section; complex construction from systematically arranged laths commonly creating a 'chequered' LM image}
Pseudolithraphidites Keupp, 1976 {nannoliths formed from 4-6 fused, circular rods; parallel sided}
Pseudomicula Perch-Nielsen in Perch-Nielsen et al., 1978 {rod with massive, expanded mid-section}

Family NANNOCONACEAE Deflandre, 1959

Description: Conical, globular or cylindrical nannoliths composed entirely of spirally-arranged platelets, enclosing an axial cavity or canal. C-axes arranged tangentially to central axis.

?Faviconus Bralower in Bralower et al. , 1989 {elongate, single or multiple columns of stacked platelets with thin axial canals}
Nannoconus Kamptner, 1931 {see description of family}

Family POLYCYCLOLITHACEAE Forchheimer, 1972 emend. Varol, 1992

Description: Nannoliths composed of two vertically-appressed wall cycles and a central-area which may be closed, open and vacant, or spanned by a diaphragm-like structure. Elements have tangential c-axis orientation.

Comments: This family has previously been used for a wide variety of nannoliths with radial, petaloid morphologies (e.g. Perch-Nielsen, 1985). Varol (1992) redefined the family to include only those forms which appear to represent a clear phylogenetic grouping, and this is followed below. Those forms which do not fall into this category are listed separately as uncertain 'polycycloliths'.

Eprolithus Stover, 1966 (= Polycyclolithus Forchheimer, 1968) {5-9 petal-like, wall-cycle elements, moderately large median diaphragm}
Farhania Varol, 1992 {16-24 rectangular, imbricating, wall-cycle elements, moderately large amedian diaphragm}
Lithastrinus Stradner, 1962 {5-7 ray-like, strongly curved, wall-cycle elements, small median diaphragm}
?Micula Vekshina, 1959 {4 blocky, strongly twisted, wall-cycle elements, joined along sutures which go out to the points of the cube; no central opening or diaphragm}
Quadrum Prins & Perch-Nielsen in Manivit et al. 1977 {4-9 ray-like, wall-cycle elements. When cubiform, the elements are joined along sutures which go out to the mid-point of the cube edges; no central opening or diaphragm}
Radiolithus Stover, 1966 (= Rhombogyrus Black, 1973) {9-16 brick-like, wall-cycle elements, large amedian diaphragm}
Uniplanarius Hattner & Wise, 1980 {3 or 4 ray-like, wall-cycle elements, small median diaphragm}

Uncertain 'polycycloliths'

Assipetra Thierstein, 1973 {solid, subrectangular-globular nannoliths formed from intergrown crystals}
Hayesites Manivit, 1971 emend. Applegate et al. in Covington & Wise, 1987 {stellate, with 6-11 dextrally imbricate rays; small subsidiary cycles and spines may be present; include only H. albiensis and H. irregularis}
Hexalithus Gardet, 1955 {form-taxon applied to 'hexaliths', i.e. hexagonal nannoliths formed from 6 elements}
Perchnielsenella Watkins in Watkins & Bowdler, 1984 {high, robust wall of ~30 imbricating elements, moderately large median diaphragm}
Polycostella Thierstein, 1971 {circular to stellate, which may exhibit 6-8 radial ridges}
Rucinolithus Stover, 1966 {stellate, formed from 5 or more ?sinistrally imbricating elements; small additional cycles may be present}
Tegulalithus Crux, 1986 {single cycle of ~16 elements forms the wall; each end of the nannolith is covered by overlapping, concentric cycles of diamond-shaped elements, becoming smaller in diameter towards the centre, thus forming a depression}

Family SCHIZOSPHAERELLACEAE Deflandre, 1959

Description: Hollow, spheroidal, bivalved nannoliths with walls constructed from a systematic geometric arrangement of small, equidimensional crystallites.

Schizosphaerella Deflandre & Dangeard, 1938 {see family description}

Mesozoic nannoliths incertae sedis

Centosphaera Wind & Wise in Wise & Wind, 1977 {keeled sphere, constructed from hour glass-shaped crystallites. Considered a calcareous dinoflagellate by Futterer, 1990}
Ceratolithina Martini, 1967 {straight or hooked rods with lateral spurs and/or blades}
Ceratolithoides Bramlette & Martini, 1964 {conical, arrowhead- or horseshoe-shaped nannoliths}
Kokia Perch-Nielsen, 1988 {rosette-shaped with 6 (8-10) or more rays (tangential c-axes); low birefringence}
Liliasterites Stradner & Steinmetz, 1984 {3-rayed; long bifurcations give a 6-rayed appearance}
Marthasterites Deflandre, 1959 {3-rayed; ray tips may bifurcate}
Orthogonoides Wiegand, 1984 {orthogonally arranged 6-rayed nannolith}
Prinsiosphaera Jafar, 1983 {solid, spherical nannolith formed from blocks of calcite laths}
?Watkinsia Covington, 1994 {large, narrowly elliptical, structureless base from which a broad, flat blade emerges}

Return to: top; Introduction, family-level overview, Mesozoic heterococcoliths, holococcoliths & nannoliths; Cenozoic heterococcoliths, holococcoliths & nannoliths

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