Glabratella californiana, from here.

Belongs within: Rotaliida.

We’ve got a thing that’s called foram love
Published 3 March 2016

It’s been a while since we last had a foram post, so why don’t we have one today? Ladies and gentlemen, I present to you: the Glabratellidae.

Pileolina patelliformis, from Brady (1884).

Glabratellids are a group of forams found in littoral habitats, first appearing in the fossil record in the Eocene (Loeblich & Tappan 1964). They secrete a calcareous test with a hyaline (glass-like) microstructure. By foram standards, glabratellids can be quite small: the smallest are well under 100 µm in diameter. They have a trochospiral body shape—that is, the body chambers are arranged in such a way that they spiral like a trochus or top shell—with a flat base. At the centre of the underside is an aperture or umbilicus. The spire may be fairly low, giving them what I always think of as a ‘jelly mould’ shape, or it may be high so their overall appearance is conical. In the genus Schackoinella, the test bears a spine on the outside of each of the body chambers.

The glory that is Schackoinella sarmatica, from the Geological Survey of Austria.

The most distinctive feature of glabratellids, perhaps, is their life cycle. We know the life cycles of relatively few foram species but as a rule they show a clear alternation of generations, with both well-developed haploid and diploid individuals. Haploid individuals (gamonts) produce gametes by nuclear mitosis that fuse to form zygotes that grow into mature diploid individuals (schizonts or agamonts); these latter produce haploid embryos via meiosis. The two generations may differ somewhat in appearance, and many foram species have had their gamonts and schizonts mistaken in the past for separate species. The most consistent difference between generations in all chambered forams is that the gamonts have a larger first chamber as a result of growing from larger embryos than the schizonts. In glabratellids, gamonts are also smaller and relatively higher-spired than schizonts, and the former are sinitrally coiled (to the left) while the latter are dextrally coiled (to the right).

The life cycle of Glabratellidae was described in detail by Loeblich and Tappan (1964) (the figure above from therein shows the lifecycle of Pileolina patelliformis). Schizonts herald the production of offspring by wrapping themselves in a protective cover of dead diatoms and other rubbish. Young gamonts are formed by nuclei dividing in the test and each becoming surrounded by their own individual cell membranes. After they form, the embryonic offspring crawl around in the parent test feeding on any leftover cytoplasm and also on the test itself. By the time they grow to about two or three chambers in size, the gamonts dissolve the umbilical wall of the parent test and escape through the aperture.

As the gamonts themselves reach maturity, their thoughts no doubt turn to their own posterity. Whereas in some other forams the haploid generation simply releases their gametes into the water column to find their own way to fusion, sexual reproduction in glabratellids is a somewhat more intimate affair. Mature gamonts form into pairs, joined to each other via their umbilical surfaces from which they will resorb the test. Locked in their embrace, the pair become cemented to the substrate. Gametes, again, are formed by the production of plasma membranes around individual nuclei; these gametes move by means of three flagella instead of by pseudopodia. The two parents exchange gametes of which only about a tenth fuse to form zygotes; the remainder provide a food source for their developed siblings. Again, the young schizonts grow to about two or three chambers in size before being released by the dissolution of the cement holding the parent tests together.

This cosy mode of reproduction means that glabratellids may have the potential for greater population differentiation than other broadcast-spawning Foraminifera. Tsuchiya et al. (2003), in a study genetic diversity in representatives of the genus Planoglabratella collected around Japan, found evidence for cryptic speciation in P. opercularis. Some individuals of this ‘species’ were closer genetically to individuals of another species P. nakamurai than to other P. opercularis, and closer inspection revealed certain details of their morphology that were more nakamurai-like than opercularis-like. It may be that we have underestimated the diversity of glabratellids, and many more species of this group remain to be discovered.

Systematics of Glabratellidae
    |--Angulodiscorbis Uchio 1953LT64b
    |    `--*A. quadrangularis Uchio 1953LT64b
    |--Schackoinella Weinhandl d1958LT64b
    |    `--*S. sarmatica Weinhandl 1958LT64b
    |--Pseudoruttenia Le Calvez 1959HW93
    |    `--*P. diadematoides Le Calvez 1959 [=Pijpersia diadematoides]LT64b
    |    |--P. nakamuraiTKP03
    |    `--P. opercularisTKP03
    `--Glabratella Dorreen 1948 [incl. Conorbella Hofker 1951, Pileolina Bermúdez 1952]LT64b
         |--*G. crassa Dorreen 1948LT64b
         |--G. australensis (Heron-Allen & Earland 1932)A68
         |--G. californiana Lankford 1973S-VC91
         |--G. erectaPB94
         |--G. mediterranensisLT64a
         |--G. opercularisLT64a [=Discorbis opercularisLT64b]
         |--G. ornatissimaLT64a
         |--G. parisiensisLT64a
         |--G. patelliformis (Brady 1884) [=Discorbis patelliformis]H03
         |--G. pileolus (d’Orbigny 1839) [=Valvulina pileolus, *Pileolina pileolus]LT64b
         |--G. pulvinata (Brady 1884) [=Discorbina pulvinata, *Conorbella pulvinata]LT64b
         `--G. sulcataLT64a

*Type species of generic name indicated


[AB19] Adl, S. M., D. Bass, C. E. Lane, J. Lukeš, C. L. Schoch, A. Smirnov, S. Agatha, C. Berney, M. W. Brown, F. Burki, P. Cárdenas, I. Čepička, L. Chistyakova, J. del Campo, M. Dunthorn, B. Edvardsen, Y. Eglit, L. Guillou, V. Hampl, A. A. Heiss, M. Hoppenrath, T. Y. James, A. Karnkowska, S. Karpov, E. Kim, M. Kolisko, A. Kudryavtsev, D. J. G. Lahr, E. Lara, L. Le Gall, D. H. Lynn, D. G. Mann, R. Massana, E. A. D. Mitchell, C. Morrow, J. S. Park, J. W. Pawlowski, M. J. Powell, D. J. Richter, S. Rueckert, L. Shadwick, S. Shimano, F. W. Spiegel, G. Torruella, N. Youssef, V. Zlatogursky & Q. Zhang. 2019. Revisions to the classification, nomenclature, and diversity of eukaryotes. Journal of Eukaryotic Microbiology 66: 4–119.

[A68] Albani, A. D. 1968. Recent Foraminiferida of the central coast of New South Wales. AMSA Handbook 1: 1–37.

[H03] Hanagata, S. 2003. Miocene-Pliocene Foraminifera from the Niigata oil-fields region, northeastern Japan. Micropaleontology 49 (4): 293–340.

[HW93] Hart, M. B., & C. L. Williams. 1993. Protozoa. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 43–70. Chapman & Hall: London.

[LT64a] Loeblich, A. R., Jr & H. Tappan. 1964a. Sarcodina: chiefly “thecamoebians” and Foraminiferida. In Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt C. Protista 2 vol. 1. The Geological Society of America and The University of Kansas Press.

[LT64b] Loeblich, A. R., Jr & H. Tappan. 1964b. Sarcodina: chiefly “thecamoebians” and Foraminiferida. In Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt C. Protista 2 vol. 2. The Geological Society of America and The University of Kansas Press.

[PB94] Pawlowski, J., I. Bolivar, J. Guiard-Maffia & M. Gouy. 1994. Phylogenetic position of Foraminifera inferred from LSU rRNA gene sequences. Molecular Biology and Evolution 11 (6): 929–938.

[S-VC91] Segura-Vernis, L. R., & A. L. Carreño. 1991. Foraminíferos y ostrácodos de la Laguna de La Paz, Baja California Sur, México. Inv. Mar. CICIMAR 6 (1): 195–224.

[TKP03] Tsuchiya, M., H. Kitazato & J. Pawlowski. 2003. Analysis of internal transcribed spacer of ribosomal DNA reveals cryptic speciation in Planoglabratella opercularis. Journal of Foraminiferal Research 33 (4): 285–293.

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