Paragloborotalia opima

Classification: pf_cenozoic -> Globigerinidae -> Paragloborotalia -> Paragloborotalia opima
Sister taxa: P. acrostoma, P. incognita, P. pseudocontinuosa, P. semivera, P. kugleri, P. pseudokugleri, P. mayeri, P. siakensis, P. birnageae, P. continuosa, P. opima, P. nana, P. griffinoides, P. sp.,


Citation: Paragloborotalia opima (Bolli, 1957)
Rank: species
Basionym: Globorotalia opima opima Bolli, 1957
Taxonomic discussion:

As P. opima and P. nana are destinguished by their size (e.g., Bolli and Saunders, 1985; Wade and others, 2016) it is very important to determine the size of their holotypes. Bolli (1957) stated that the holotype of P. opima was 0.55 mm, however, our investigations indicate this is incorrect. Adding to the confusion, the holotype of P. opima was first illustrated by SEM in Olsson and others (2006) (pl. 5.8, figs. 13-15), however, the scale bar in the figure is not accurate. Through this work we re-examined the holotype at the USMN have determined that the 5 chambered holotype specimen (USNM P5659) is 0.45 mm, and the 4 chambered paratype (USNM 5660) is 0.48 mm.

Bolli and Saunders (1985) referred to specimens of the opima-nana plexus that were between 0.32 and 0.39 mm as ‘transitional’ intermediate forms. However, given the stratigraphic utility of P. opima it is critical to classify the transitional forms for recognition of the base of Zone O6. Morphometric analysis was conducted on specimens of the opima-nana plexus from IODP Site U1334 in the equatorial Pacific Ocean by Wade and others (2016). They determined that shape outline (quadrateness) and number of chambers were not useful criteria to separate the two forms and concluded that size was the only delimiting character. The ‘transitional’ forms of Bolli and Saunders (1985) (i.e., >0.32 mm) are thus consistent with P. opima.

Both P. nana and P. opima typically possess the same number of chambers in the final whorl, indicating that the increased size in P. opima is not a form of heterochrony but giantism of the ancestral P. nana form (Wade and others, 2016). [Leckie et al. 2018]

Catalog entries: Globorotalia opima opima

Type images:

Distinguishing features:

Like P. nana but larger (>0.32mm)

NB These concise distinguishing features statements are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus.
They are being edited as the site is developed and comments on them are especially welcome.


Diagnostic characters:

The criterion for separating P. opima from P. nana is strictly size, with P. nana (Bolli and Saunders, 1985; Wade and others, 2016). The holotype of P. opima has 5 chambers in the final whorl, and a diminutive final chamber (Pl. 5.8, Figs. 1-3). As stated by Bolli and Saunders (1985), the 5 chambered forms are typically rare and we consider the 4 chambered paratype with its large, embracing final chamber (Pl. 5.8, Figs. 9-11) to be more characteristic of the form based on our experiences. In general, the lip in P. opima is less pronounced and thinner than in P. nana. The position of the final chamber against the first chamber (of the final whorl) also prevents the cross-shaped suture pattern that is a common feature of P. nana s.s. Greater chamber inflation is common in the largest specimens of P. opima, resulting in a bulbous final chamber (Wade and others, 2016). In addition, some larger specimens of opima may display a more rapid expansion in thickness resulting in the slight depression of the inner spire.

Paragloborotalia opima is distinguished from P. pseudocontinuosa by its more compact test and lower arched aperture. Bolli and Saunders (1985) suggested that the forms they considered as opima-nana transitions (between 0.32 and 0.39 mm), which more commonly have 5 chambers, may be ancestral to P. mayeri. We reject this hypothesis and consider P. siakensis as the direct ancestor of P. mayeri. Paragloborotalia opima can be distinguished from P. mayeri, by its lower arched aperture, radial spiral sutures, and fewer number of chambers in the final whorl. It can be distinguished from P. siakensis by its rounder, more embracing chambers, less well developed lip, and less lobulate periphery. Paragloborotalia opima is distinguished from Parasubbotina varianta by a slower rate of chamber growth and inflation, more embracing chambers, a lower aperture, and generally more heavily encrusted test. [Leckie et al. 2018]

Wall type: Normal perforate, coarsely cancellate, probably sparsely spinose in life, heavy gametogenetic calcification is often present.

Test morphology: Test large in size; very low trochospiral, generally quadrate to slightly lobulate in equatorial outline, chambers globular, inflated, embracing; commonly 4, sometimes 4½-5 chambers in ultimate whorl, increasing moderately in size; in spiral view chambers moderately to strongly inflated, spherical to subspherical, arranged in 2-2½ whorls, sutures depressed, radial, ultimate chamber may be slightly reduced in size; in umbilical view chambers strongly inflated, spherical, sutures depressed, radial, umbilicus very narrow to nearly closed, moderately deep, sometimes closed off by surrounding chambers, ultimate chamber may be slightly reduced in size; aperture umbilical-extraumbilical, low arch, bordered by a narrow, often thickened, continuous rim or lip; in edge view chambers globular, spiral side nearly flat to slightly depressed, periphery broadly rounded. [Leckie et al. 2018]

Size: Maximum diameter of holotype 0.45 mm, maximum thickness 0.31 mm (this study). [Leckie et al. 2018]

Character matrix

test outline:Lobatechamber arrangement:Trochospiraledge view:Equally biconvexaperture:Umbilical-extraumbilical
sp chamber shape:Globularcoiling axis:Lowperiphery:N/Aaperture border:Thick lip
umb chbr shape:Globularumbilicus:Narrowperiph margin shape:Broadly roundedaccessory apertures:None
spiral sutures:Weakly depressedumb depth:Shallowwall texture:Cancellateshell porosity:Macroperforate: >2.5µm
umbilical or test sutures:Moderately depressedfinal-whorl chambers:4.0-5.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Cosmopolitan, including the tropics and high northern latitudes, e.g., Site 407 (63oN) (Poore, 1979). Larger and more abundant in eutrophic environments (Wade and others, 2007, 2016). [Leckie et al. 2018]

Isotope paleobiology: Multispecies stable isotope analyses by Biolzi (1983) and Poore and Matthews (1984) suggest a thermocline habitat, consistent with Wade and others (2007) and Matsui and others (2016). [Leckie et al. 2018]

Phylogenetic relations: Evolved from P. nana in lower Oligocene Zone O2, and did not leave any descendants. [Leckie et al. 2018]

Most likely ancestor: Paragloborotalia nana - at confidence level 4 (out of 5). Data source: Leckie et al. 2018.

Biostratigraphic distribution

Geological Range:
Notes: Paragloborotalia opima has a restricted stratigraphic range relative to P. nana and P. siakensis, a feature that has been utilized in biostratigraphic schemes (e.g., Bolli, 1957; Bolli and Saunders, 1985; Berggren and others, 1995; Berggren and Pearson, 2005; Wade and others, 2011). Its base occurrence has been calibrated to 30.6 Ma (Berggren and others, 1995). The highest occurrence of P. opima defines the O5/O6 zonal boundary at 27.5 Ma within Chron C9n (Wade and others, 2007, 2011, 2016). [Leckie et al. 2018]
Last occurrence (top): at top of O5 zone (100% up, 26.9Ma, in Chattian stage). Data source: Leckie et al. 2018
First occurrence (base): in upper part of O2 zone (80% up, 30.6Ma, in Rupelian stage). Data source: Leckie et al. 2018 f5.1

Plot of occurrence data:

Primary source for this page: Leckie et al. 2018 - Olig Atlas chap.5 p.153


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Paragloborotalia opima compiled by the pforams@mikrotax project team viewed: 29-3-2020

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