Three Random Foram Genera (Taxon of the Week: Pelosininae)

In an earlier post, I introduced you to the agglutinated forams of the family 'Saccamminidae'. As explained in that post, 'Saccamminidae' is undoubtedly a polyphyletic assemblage of forams of very simple morphology. In the influential, and outdated, classification of Cushman (1940), 'saccamminids' were divided between four subfamilies for which odds are that each of those subfamilies are as polyphyletic as the whole. Let's take a look at the members of one of those subfamilies and see where they are now.


Pelosina variabilis. Photo by Jan Pawlowski.

The subfamily Pelosininae, as recognised by Cushman (1940), included the genera Pelosina, Technitella and Pilulina. The distinguishing characteristics of this subfamily were that its members had free, unattached tests with a single chamber, at least one aperture and walls composed of fine particles. All three also live in the deep sea and include relatively large species for forams (up to 60 mm in height in Pelosina). In the classification of Kaminksi (2004), none of these genera were closely associated. In the case of Pelosina, Cushman was not even correct about the few defining features of the subfamily because this genus does live attached to the sediment by root-like structures (Rützler & Richardson 1996). Pelosina species are one of a number of tree-like forams that form a significant component of the deep-sea benthic community.


Technitella legumen. Image from here.

Technitella, in contrast, is an elongate, somewhat sausage-like form. The name of the genus ("little workman") refers to its elegantly constructed test, constructed from carefully selected materials. Heron-Allen & Earland (1909) described one species, T. thompsoni, which uses nothing but brittle star plates while T. legumen prefers sponge spicules, arranged in two layers with the spicules in each layer at right angles to each other to strengthen the test. Heron-Allen and Earland mused that "Probably we should be considered as imposing too weighty a postulate upon the members of the Club if we ventured to suggest that these rudimentary organisms were gifted with any aesthetic sense... it would appear that this "primordial, protoplasmic, atomic globule" is by no means so elementary an organism as naturalists are inclined to believe".


Lectotype and paralectotype of Pilulina jeffreysii. Photo by Andrew Henderson.

Finally, Pilulina constructs a globular test of felted sponge spicules with an elongate aperture like the mouth on a stick-figure's face. Of the three genera, only Pelosina and Pilulina have appeared in molecular phylogenetic analyses and the two do not appear to be associated, sitting instead in separate parts of the saccamminid cloud (e.g., Lecroq et al., 2009). Mikhalevich & Voronova (1999) argued that Pelosina is in fact a xenophyophore and placed it in the order Stannomida with the genera Stannoma and Stannophyllum. This was based on the supposed presence of linellae, a structure only otherwise found in stannomids. No molecular analysis has indicated an association between Pelosina and other xenophyophores. However, no other stannomid has appeared in these analyses, so just because Pelosina is not directly related to xenophyophores may not necessarily mean that it is not directly related to stannomids.

REFERENCES

Cushman, J. A. 1940. Foraminifera: their classification and economic use, 3rd ed. Harvard University Press: Cambridge (Massachusetts).

Heron-Allen, E., & A. Earland. 1909. On a new species of Technitella from the North Sea, with some observations upon selective power as exercised by certain species of arenaceous Foraminifera. Journal of the Quekett Microscopical Club, second series 10: 403-412.

Kaminski, M. A. 2004. The Year 2000 classification of the agglutinated Foraminifera. In: Bubík, M. & M. A. Kaminski (eds) Proceedings of the Sixth International Workshop on Agglutinated Foraminifera. Grzybowski Foundation Special Publication 8: 237-255.

Lecroq, B., A. J. Gooday, T. Cedhagen, A. Sabbatini & J. Pawlowski. 2009. Molecular analyses reveal high levels of eukaryotic richness associated with enigmatic deep-sea protists (Komokiacea). Marine Biodiversity 39: 45-55.

Mikhalevich, V. I., & M. N. Voronova. 1999. O sistematicheskom polozhenii roda Pelosina (Xenophyophoria, Protista, inc. sedis). Zoologicheskii Zhurnal 78 (2): 133-141.

Rützler, K., & S. Richardson. 1996. The Caribbean spicule tree: a sponge-imitating foraminifer (Astrorhizidae). Bulletin de l'Institut Royal des Sciences Naturelles de Belgique 66 (Suppl.): 143-151.