Ultrastructure, Morphology, Affinities and Reclassification of Cassigerinella Pokorny (Foraminiferida: Globigerinina)

J.rnicropalaeontol., 5 (2): 49-64, December 1986 Ultrastructure, morphology, affinities and reclassification of Cassigerinella Pokorny (Foraminiferida: Globigerinina) LI QIANYU Postgraduate Unit of Micropalaeontology, University College London, Gower Street, London WClE 6BT* ABSTRACT - Re-examination of Cassigerinella chipolensis (Cushman & Ponton) and comparison of the ultrastructure of its morphotypes demonstrates that the species should only contain forms with a smooth surface and that those with a pore-cone surface should be distinguished as the type species, C. boudecensis Pokorny, a name which is still valid both taxonomically and stratigraphically. Strong resemblance in surface structure, aperture pattern and essential biseriality between many heterohelicids and Cassigerinella has been considered to be significant for its reclassification. Cassigerinella is, therefore, believed to have originated among the Heterohelicacea rather than in the Globigerinacea or Hantkeninacea as previously proposed by various authors. Morphological features, such as apertural modifications and coiling mode, and the characteristics of several related taxa of the species-group are discussed. INTRODUCTION Some thirty years ago, PokornL (1955) established a losa Egger, 1857, from the Miocene of Germany), C. new planktonic genus, Cassigerinella, to embrace the chipolensis ( = Cassidulina chipolensis Cushman & forms with biserial-enrolled and inflated chambers Ponton, 1932, from the Early Miocene of Florida), C. within the family Orbulinidae (= Globigerinidae, see winniana (= Cassidulina winniana Howe, 1939, from Pokorny, 1958, p. 346). The type species, C. the Eocene of Louisiana), C. globolocula Ivanova boudecensis Pokornf, 1955, is characterised, according (1958, from the Late Oligocene of USSR), C. regularis to Pokorny, by an initial planispiral test with a high@ Iturralde Vinent (1966, from the Oligocene of Cuba), arched aperture and a papillose surface, which were C. martinezpicoi ( = Riveroinella martinezpicoi Ber- believed to be quite distinctive if compared with mudCz & Seiglie, 1967, from the Early Miocene of Cassidulina chipolensis Cushman & Ponton, 1932, a Puerto Rico) and C. eocaenica Cordey (1968, from the species which was also considered to be a Cassigerinella Eocene of Florida). All of these, except C. regularis, by Pokorny (op. cit.) in his generic descriptions. Later, are distinguished by a small test with a diameter of, basing their interpretation on the planispire in the early commonly, 0.1-0.25mm. Among them, the most fre- stage as described by Pokorny for the type species, quently used species names are chipolensis and win- Bolli, Loeblich & Tappan (1957, p. 30) believed that niana; the former is said to be a subjective senior Cassigerinella should be referred to the Hantkeninidae synonym of both boudecensis and globolocula, and the rather than to the Globigerinidae. They further sepa- latter a senior synonym of eocaenica (see Kennett & rated the genus from other hantkeninids by creating for Srinivasan, 1983, p. 18; Blow, 1979, pp. 1361-1364). In it a separate subfamily - the Cassigerinellinae. In lacking accurate original descriptions and drawings and various later biostratigraphic and taxonomic studies the available topotypes, the oldest name, globulosa, had suprageneric position of Cassigerinella has never been not been used and referred to the genus until Rogl agreed, and the genus has been placed, mainly, either (1985) reused it, even though Pokorny (1955) did in the Hantkeninidae (e.g. Loeblich & Tappan, 1964, mention that Egger’s globulosa was undoubtedly a 1984; Bolli & Saunders, 1985) or among the Globigeri- Cassigerinella. Nevertheless, the criteria for discrimina- nidae (e.g. Banner & Blow, 1959; Blow, 1969, 1979). tion among these species (excluding regularis and The main cause of the dispute seems to be belief in the martinezpicoi) are still so inadequately defined that presence or absence of the initial planispiral stage in many workers could often be confused and unable to Cassigerinella. differentiate them when coming across these tiny Apart from its type species, C. boudecensis, other planktonic forms in the mid-Tertiary sequences. species which have been referred to the genus under Another morphocharacter of Cassigerinella to which discussion include: C. globulosa ( = Cassidulina globu- taxonomic significance has been attached is the tooth- *now at: Department of Geology, Zhongshan (Sun Yat Sen) University, Guangzhou, Peoples’ Republic of China. 49 Li Qianyu plate structure observed by Hofker (1963) and, subse- once have existed. Unfortunately, little satisfactory quently, confirmed by Steineck & Darrell (1971). This information has been supplied, to date, to support character, which has been seen in many benthic forms these assumptions, possibly because of the relative but never in the planktonics, led the authors cited to rarity of some species (not chipolensis) and because of consider that the genus should belong to neither the the difficulties either in collecting suitable material or Globigerinidae nor the Hantkeninidae but to the in examining the extremely tiny tests possessed by Cassidulinidae or Islandiellidae. The presence of a true many Cassigerinella species. toothplate and its supposed significance were no longer As an attempt to clarify some of these problems, the accepted after Saito & Biscaye (1977) supplied evi- present work was carried out with a comparison and dence to prove that the alleged toothplate structures of re-examination of specimens from the Oligocene of the any Cassigerinella were merely apertural lips, flanges or Cipero Formation (type locality of the opima opima other apertural modifications only. However, the Zone, P21) of Trinidad, the Cipero type section, relationship between the apertural flanges, protruding between 20 and 240 feet southwest from the Fixed teeth and toothplates is a problem which has not yet Point along the Cipero coast (see Bolli, 1957, pp. 100, been satisfactorily interpreted, and one that still needs 103-105, fig. 19). Many specimens of C. chipolensis to be resolved. were dissected and observed with the aid of a JEOL- Taking into account the enrolled-biserial nature of T20 scanning electron microscope in the Micropalaeon- the tests of Cassigerinella and the peculiar aperture tology Unit of University College London. Also, the pattern, Blow (1979) suggested that a separate and holotype and paratype of C. eocaenica Cordey, depo- distinct family was warranted for this genus; the sited in the British Museum (Natural History) were presence of only pseudoumbilici, and no true umbilici, re-examined. in this form also led him to consider it to be, more likely, an enrolled heterohelicid rather than a hantkeni- RESULTS nid or globigerinid, and to represent a finally extreme Approximately 200 individuals of Cassigerinella from modification of some small tests of the Heterohelicacea Zone P21, Trinidad, were examined; they contained known in the later Middle Eocene. Kennett & Sriniva- two distinct morphotypes: one is covered with numer- san (1983) paid more attention to the resemblance in ous pustule-like cones around the perforations on the the surface ultrastructure of Cassigerinella to those of wall surface whilst the other possesses a smooth, Chilogeumbefina and Streptochilus, and suggested that pustule-less surface structure. Both morphotypes are a phylogenetic relationship between these forms might described and discussed below. Explanation of Plate 1 Cassigerinella boudecensis Pokorny 1955 (All figures on P1. 1, as well as other specimens figured on PIS. 2-4, were from opima opima Zone(P21) of the Cipero Formation, Trinidad). Figs. 1, 2, 3. Apertural views of three specimens. Showing sparsely to densely developed pore-cones, asymmetrical apertures and apertural flanges: fig. 1, X250; fig. 2, ~170;fig. 3, X170. Figs. 4-5. A specimen with twisted coiling (see also Fig. 1) and a weak apertural flange: fig. 4, X 170; fig. 5, enlargement of the aperture, ~500. Figs. 6,7. Two dissected specimens showing nearly symmetrical apertures and flanges on the penultimate chambers: fig. 6, x250; fig. 7, x335. Figs. 8-9. A specimen with symmetrical, highly arched aperture: fig. 8, ~120;fig. 9, enlargement of the aperture, x500. Figs. 10-11, 12-13. Two dissected specimens with the aperture and pore-cones developed in various degrees: fig. 10, X170; fig. 11, enlargement, ~665;fig. 12, X335; fig. 13, enlargement, ~665. Figs. 14-15. A heavily walled specimen with dissection to show the low arched aperture without toothplate: fig. 14, x335; fig. 15, enlargement, ~665. Fig. 16. A dissected specimen showing absence of the toothplate structure, x250. Figs. 17-18. A heavily pore-coned specimen: fig. 17, ~175;fig. 18, enlargement of the pore-cones, X665. Reclassification of Cassigerinella Pokorng 51 Li Qianyu Coiling mode. asymmetrical (Pl. 1, figs. 1-4; P1. 4, figs. 1-5) or nearly All examined specimens of both morphotypes show, symmetrical (Pl. 1, figs. 7-10; P1. 3, figs. 1, 10). It seems as in benthic Cassidulina, a biserially enrolled test that there is no rule for the development and geometric throughout ontogeny. No tests with an initially planis- modification of the aperture during ontogeny. piral stage nor globigerine coiling mode have been A discontinuously developed apertural rim is always found, though some specimens had externally the seen in many tests although its growth may be of appearance of being planispired initially. In the latter various degrees. Those

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