I'm going to slack off a bit this time. For an overview of the huge clade of awesome that is Foraminifera, see my earlier post here; for another tree foram, see Notodendrodes here.
Foraminiferans are amazing creatures: some of them can be best described as giant cannibalistic carnivorous wads of sticky reticulated pseudopodia, capable of snaring and devouring small metazoans and Volvox colonies. They have the fastest microtubule growth rates in the eukaryotic kingdom - a whole two orders of magnitude greater than those of animals at a stunning 12µm/s! (animal cells grow microtubules at around 1-15µm/min.) (Bowser & Travis 2002 J Foram Res) Their pseudopodia are themselves capable of shearing flesh in a process so unique it deserved its own name: 'skyllocytosis' (Bowser 1985 J Protozool). Do not screw around with forams. They are scary.
Most of them also have shells, but that's a story for some other day. Well, many stories, for many days. Forams are a huge and diverse group.
The following specimen belongs to Astrorhizidae, a group of agglutinating forams - meaning their tests are composed of material from the environment, often very selectively picked. As implied by its name, the spicule tree, or Spiculidendron, composes its test entirely out of sponge spicules. Furthermore, this contraption reaches a stunning 60mm (6cm) in height, as a single-celled organism!
Plant, animal or protist? A foram tree to shame all foram trees. A giant spicule-covered monster from the Caribbean tropics. (Rützler & Richardson 1996 Biologie)
The paper mentions difficulties in determining whether the spicule tree bears a single nucleus or is coenocytic. Presumably, if it was that hard to find (though they had few specimens to work with), it may well be uninucleate like Notodendrodes. This would be quite cool as 6cm is one hell of a giant cell to be supported by a single nucleus. The cytoplasm also contains symbiotic dinoflagellates, making this tree foram even more like an actual tree.
Note that this strange monster of a foram was only described in 1996. The age of exploration is far from over.
Rützler, K., & Richardson, S. (1996). The Caribbean spicule tree: a sponge-imitating foraminifer (Astrorhizidae) Bulletin de l'Institut Royal des Sciences Naturelles de Belgique 66 (Suppl.), 143-151
Bowser, S. (2002). RETICULOPODIA: STRUCTURAL AND BEHAVIORAL BASIS FOR THE SUPRAGENERIC PLACEMENT OF GRANULORETICULOSAN PROTISTS The Journal of Foraminiferal Research, 32 (4), 440-447 DOI: 10.2113/0320440
BOWSER, S. (1985). Invasive Activity of Allogromia Pseudopodial Networks: Skyllocytosis of a Gelatin/Agar Gel The Journal of Eukaryotic Microbiology, 32 (1), 9-12 DOI: 10.1111/j.1550-7408.1985.tb03005.x