THE UNIVERSITY OF KANSAS

PALEONTOLOGICAL CONTRIBUTIONS

November 30, 1967 Paper 28

NANNOFOSSIL SPECIES RELATED TO CYCLOCOCCOLITHUSLEPTOPORUS (MURRAY & BLACKMAN)

STEFAN GARTNER, JR.[Esso Production Research Company, Houston, Texas]

ABSTRACT

Individual placoliths of the coccolithophore Cyclococcolithus leptoporus often breakapart into two shields. The genera Tiarolithus (type species, Calcidiscus medusoides) andCalcidiscus (type species, C. quadriforatus) are based on species here recognized as repre-senting isolated distal and proximal shields, respectively, of Cyclococcolithus leptoporus.Tiarolithus, and Calcidiscus, therefore, are junior (subjective) synonyms of Cyclococcolithus.

DISCUSSION

In 1897 GEORGE MURRAY & V. H. BLACKMANcollected several samples of sea water from theNorth Atlantic and Caribbean while making around trip from England to Panama on the mail-ship R. M. S. Para. Their purpose was to studythe nature of coccospheres and rhabdospheresfrom these waters and to test techniques for ex-tracting the minute organisms from the sea water.In the course of their investigation they noted aspecies of coccolithophore that had not been de-scribed or named previously. They named thisspecies Coccolithophora leptopora and describedthe coccoliths of the species as follows:

The coccolith is seen to possess two distinct limbsjoined together by a central thick-walled collar. Theouter limb is a round plate, convexo-concave in section,very like an inverted shallow watch-glass; the inner limbis a small circular flat plate; the two plates are joinedtogether by a central collar. On the convex free surfaceof the outer plate there is a minute circular depressionappearing in surface view as a clean area. The bottom ofthis depression is perforated by a canal which leadsthrough the collar and opens out on the free surface ofthe lower limb.

Their description is of a circular placolithwhich has a larger distal shield and a smallerproximal shield, the two shields being connected

at their centers by a hollow tube. The same au-thors noted also that some of the "plates" (placo-liths) of this species have radial "striations"(sutures) whereas others seem to have curved"striations." In their illustrations they show bothtypes of specimens, some with straight radial su-tures, others with curved sutures (MURRAY &BLACKMAN, 1898, pl. 15, fig. 12). Another impor-tant feature that they discuss is the continuationof some of the radial striations in the conical de-pression at the center of the distal shield of theplacolith. In their illustrations (MURRAY & BLACK-MAN, 1898, pl. 15, fig. 4-5) these radial striationsappear to be coarser or more pronounced in thedepression than on the surface of the shield so thatthis central depression also gives the appearanceof being partially obstructed by coarse, radiallydisposed ribs or bars.

In 1954 KAMPTNER redescribed the species inconsiderable detail and assigned it to the genusCycloccolithus and in 1962 HAY & TOWE desig-nated Coccosphaera leptopora as the type speciesof that genus. KAMPTNER noted several importantfeatures of the species which are significant for acorrect interpretation. When viewed distally, su-tures on the distal shield are curved and the con-

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The University of Kansas Paleontological Contributions—Paper 28

vex side of the curvature is toward the clockwisedirection. He also confirmed that specimens mayhave curved or straight radial sutures. In additionhe noted that in cross-polarized light the specieshas a slightly rotated crosslike interference figurebut that this figure extends only as far as thesmaller proximal shield overlaps the larger distalshield. He attributed the interference figure tothe cumulative effect of both shields on the polar-ized light beam, stating that the distal shield didnot produce a sufficient path difference in thelight by itself to form an interference figure. Itshould be noted also that the distal shield of theplacolith of this species shows considerable reliefin plain transmitted light and in phase contrast.The proximal shield, however, is barely visible un-less the placolith is viewed in cross-polarized light.In that case the proximal shield is sharply defined,whereas the distal shield is only faintly visible (Pl.1, fig. 4a-c).

The exact nature of the straight radial andcurved sutures of Cyclococcolithus leptoporus firstnoted by MURRAY & BLACKMAN (1898), and laterby KAMPTNER (1954) was determined by examin-ing electron micrographs of carbon replicas of thisspecies (Pl. 1, fig. 1-2). In Pl. 1, fig. 1 part of theproximal surface of the distal shield is exposedwhere the proximal shield is broken, and suturesvisible on the distal shield are nearly straight andradial. In Pl. 1, fig. 2 the preserved half of thedistal shield clearly shows that sutures on the dis-tal surface of the distal shield are curved, with theconvex side of the curvature toward the clockwisedirection. This is explained readily because theproximal surface of the distal shield of Cyclococ-colithus leptoporus is nearly flat to very slightlyconcave. Thus, inclined planes separating adjacentelements of the shield intersect the nearly flatproximal surface of the distal shield in a straightline, thereby forming the straight, radial sutureson this surface. The distal surface of the distalshield, on the other hand, is strongly convex, andthe intersection of the inclined planes that separateadjacent elements and of the curved distal surfaceof the shield, result in curved suture lines on thedistal surface. Thus, with a light microscope it ispossible, for example, to see radial and curvedsutures on the same specimen of this speciesmerely by varying the focus on a given specimen,as was observed by KAMPTNER (1954).

Some small specimens of Cyclococcolithus lep-

toporus, furthermore, definitely have curved su-tures on the proximal surface of the distal shield(Pl. 1, fig. 3). This probably results from thegreater amount of curvature of the shield in thesesmall specimens. Sutures on the proximal shieldof this species are straight and radial on both sur-faces (Pl. 1, fig. 1-2; Pl. 2, fig. 2) indicating thatthe shield is very nearly flat and of relatively uni-form thickness.

KAMPTNER also described in considerable de-tail the species Calcidiscus medusoides (KAMPT-NER, 1954, p. 26-33, fig. 24-34) and later desig-nated this species as the type of the genus Tiaro-lithus ( KAMPTNER, 1958). Calcidiscus medusoidesconsists of a concavo-convex shield that is perfo-rated at its center and has a hemispherical knobin the center of the concave or proximal surface.KAMPTNER (1954) indicated that the sutures arecurved on both surfaces of the shield, being thesame on the distal surface as they are on Cyclococ-colithus leptoporus ( KAMPTNER, 1954, fig. 34). InKAMPTNER ' S drawing the sutures on the proximalsurface of Calcidiscus medusoides curve in thesame way as on the distal surface, although theyappear the reverse because the specimen is viewedfrom the opposite side (KAMPTNER, 1954, fig. 24).Close examination of Calcidiscus medusoides re-veals that the sutures always are curved on the dis-tal or convex surface but are commonly very nearlystraight and radial on the proximal or concavesurface of the shield, precisely as is the case withthe distal shield of Cyclococcolithus leptoporus.Only by imprecise focusing or on small specimenscan curved sutures be seen on the proximal surfaceof the shield. Calcidiscus medusoides does notyield a crosslike interference figure in cross-polar-ized light when a specimen is viewed either prox-imally or distally but instead an ill-defined brightarea appears near the center and becomes weakand disappears toward the edge of the shield (Pl.2, fig. 4e; see also MARTINI & BRAMLETTE, 1963, pl.102, fig. 1-2).

In addition to its unusual interference figurethis species is conspicuous in the light microscopebecause of its strong optical relief; that is, it iseasily visible against the background even in plaintransmitted light without the use of phase optics(Pl. 2, fig. 4a,b,d), just as is the case with the dis-tal shield of Cydococcolithus leptoporus. This isdue doubtless to the peculiar orientation of thecalcite crystals that make up the elements of the

Gartner—Nannofossil Species Related to Cyclococcolithus Leptoporus 3

shield of Tiarolithus medusoides, the same phe-nomenon that is responsible for the unusual inter-ference figure of this species in cross-polarizedlight. Thus, construction as well as crystallo-graphic properties indicate that T. medusoides(=Calcidiscus medusoides) is nothing more thanthe isolated distal shield of C. leptoporus. The fre-quency with which broken and otherwise dam-aged specimens of C. leptoporus are encounteredtends to lend support to the conclusion that thetwo shields of this placolith often do separate, andeven can lead to deceptive conclusions about thestratigraphic occurrence of the parent structureand its various parts (see MARTINI & BRAMLETTE,1963).

It remains to be shown what happens to theproximal shield of Cyclococcolithus leptoporuswhen the two shields separate, for, theoretically atleast, an isolated proximal shield must exist forevery isolated distal shield. Actually, it appearsthat the proximal shield is more readily brokeninto smaller fragments than the distal shield, sothat commonly fewer proximal shields are foundin one piece. Also the proximal shield of C. lepto-porus has very low optical relief, as can be seen inlight micrographs (Pl. 1, fig. 4a-c) where theproximal shield of whole specimens rarely is visi-ble except in cross-polarized light. As mentionedpreviously, sutures on both sides of the proximalshield are straight and nearly radial and on carbonreplicas can be seen more distinctly on the distalside of the shield (PI. 1, fig. 2; PI. 2, fig. 2) thanon the proximal side (Pl. 1, fig. 1,3). With thelight microscope the sutures are only barely visible(Pl. 2, fig. 3a-c). Some specimens of C. leptoporus(Pl. 1, fig. 3) show an irregular set of bars, com-monly 4 to 7, extending partly across the centralperforation, and remnants of such bars can be seenalso in the center of an isolated proximal shield(Pl. 2, fig. 2). Thus, in specimans of C. leptoporushaving bars developed across the central perfora-tion, these bars commonly remain with the prox-imal shield upon separation of the shields. Occa-sionally distal shields with remnants of bars in thecenter also are encountered (MARTINI & BRAM-

SAM

The Sigsbee knoll core samples used in thisstudy were obtained through the courtesy of Dr.W. BRYANT and Mr. T. E. PYLE Of Texas A & MUniversity and are from core 64-A-9-5 taken by theresearch vessel Alaminos near the crest of one of

LETTE, 1963, pl. 102, fig. 1, 2). If small allowancesare made for the strongly interpretive drawings ofKAMPTNER, then the type species of Calcidiscusquadriforatus KAMPTNER can be identified as theproximal shield of C. leptoporus (see KAMPTNER,1954, fig. 35-37). The two are nearly identical inall particulars. C. quadriforatus is only slightlycurved and of uniform thickness as is the proximalshield of C. leptoporus. Both have low optical re-lief and a very sharp interference figure in cross-polarized light; the interference figure is rotatedabout 15° to counterclockwise. [In the illustrationPl. 2, fig. 3c, this rotation is reversed because of

the peculiarity of the optical system with whichthe photograph was made.] In both the suturesare barely or not at all visible, and both have aslightly smaller average diameter than Tiarolithusmedusoides, the larger distal shield of C. lepto-porus.

The similarity of Tiarolithus medusoides andCalcidiscus quadriforatus to the distal andproximal shields, respectively, of Cyclococcolithusmedusoides was recognized by KAMPTNER (1958,p. 81). He believed that the two shields resultedfrom "backwards development" (Rueckbildung)of C. medusoides; that is, two "phylogeneticdevelopmental series" originating from the parentform, Cyclococcolithus leptoporus. In one (T.medusoides), the proximal shield does not develop,whereas in the other (C. quadriforatus) the distalshield and collar do not develop. Nothing can beseen on electron micrographs to indicate that suchis the case. Rather, all isolated shields show evi-dence of breakage, and in no case is there any evi-dence of rudimentary development of the missingpart, which would be expected if a part were re-duced progressively as is suggested by KAMPTNER.

In summary, then, the genera Tiarolithus (typespecies Calcidiscus triedusoides) and Calcidiscus(type species Cakidiscus quadriforatus) are basedon species representing incomplete placoliths ofCyclococcolithus leptoporus. They are subjectivejunior synonyms (metanyms) of Cyclococcolithusand, therefore, should not be used.

PLESthe Sigsbee knolls. The core has been described indetail by BRYANT & PYLE ( 1965 ) and PYLE (1966).Dr. A. H. COOGAN, of Esso Production ResearchCompany, collected the sample from the top ofthe San San Clay at San San Bay in Jamaica.

4 The University of Kansas Paleontological Contributions-Paper 28

ILLUSTRATIONS

PLATE 1, FIGURES 1-4. Cyclococcolithus lep-toporus.-1. Proximal view of specimen, partof proximal shield broken away exposing prox-imal surface of distal shield; electron micrograph,X10,000; from the 200-cm. level of Sigsbee knollcore, Gulf Mexico. 2. Distal view of specimenwith part of distal shield broken away, exposingdistal surface of proximal shield; electron micro-graph, X10,000; from 200-cm level of Sigsbeeknoll core, Gulf Mexico.-3. Proximal view ofsmall specimen on which sutures on proximalsurface of distal shield are curved and several barsextend partly across perforation at center of cocco-lith; electron micrograph, X10,000; from near thetop of the San San Clay of Jamaica. 4. Distalview of complete specimen from the 250-cm. levelof Sigsbee knoll core; light micrographs, X2,500;4a, phase contrast, 4b, bright field, 4e, cross-polar-ized light; note that proximal shield of this speci-men is only very faintly visible in phase contrast

and bright field, but has a distinct pseudointer-ference figure in cross-polarized light.

PLATE 2, FIGURES 1-4. Cyclococcolithus lep-toporus.-1. Proximal view of discrete distal shield;electron micrograph, X10,000; from 200-cm. levelof Sigsbee knoll core, Gulf Mexico. 2. Distalview of isolated proximal shield; electron micro-graph, X10,000; from 400-cm. level of Sigsbeeknoll core, Gulf Mexico (note short bars extend-ing partly across central perforation.)--3. Distalview of isolated proximal shield; light micro-graphs, X2,500; from 250-cm. level of Sigsbeeknoll core, Gulf Mexico; 3a, phase contrast, 3b,bright field, 3e, cross-polarized light.-4. Prox-imal and side views of isolated distal shield; lightmicrographs, X2,500; from the 200-cm. level ofSigsbee knoll core, Gulf Mexico; 4a, phase con-trast, proximal view; 4b, bright field, proximalview; 4c, cross-polarized light, proximal view; 4d,bright field, side view.

REFER ENCES

BRYANT, W. R., & PYLE, T. E., 1965, Tertiary sedimentsfrom Sigsbee knolls, Gulf of Mexico: Am. Assoc. Pe-troleum Geologists, Bull., v. 49, p. 1517-1518.

HAY, W. W., & TOWE, K. M., 1962, Electronmicroscopicexamination of some coccoliths from Donzaq (France):Eclogae Geol. Helvetiae, v. 55, p. 497-517, 2 fig., 10 pl.

KAmPTNER, Enwix, 1954, Untersuchungen ueber den Fein-bau der Coccolithen: Archiv Protistenkunde, v. 100, P.1-90, 50 fig.

, 1958, Betrachtungen zur Systematik der Kaik -flagellaten, nebst Versuch einer neuen Grupierung derChrysomonades: Archiv Protistenkunde, v. 103, p. 54-116.

MARTINI, ERLEND, & BRAMLETTE, M. N., 1963, Calcareousnannoplankton from the experimental MoholeJour. Paleontology, v. 37, p. 845-856, fig. 1-2, pl. 102-105.

MURRAY, GEORGE, & BLACKMAN, V. H., 1898, On the natureof coccospheres and rhabdospheres: Royal Society (Lon-don) Philos. Trans., ser. B, v. 190, p. 427-441, pl.15-16.

PYLE, T. E., 1966, Micropaleontology and mineralogy of aTertiary sediment core from the Sigsbee knolls, Gulf ofMexico: Texas A & M University, Department ofOceanography, Tech. Rept. 66-13T, 107 p., 4 fig., 8 pl.

THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONSGartner—Nannofossils of Cyclococcolithus leptoporus type Paper 28, Plate 1

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THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONSPaper 28, Plate 2 Gartner—Nannofossils of Cyclococcolithus leptoporus type