Dracomyxa pallida gen. et sp. nov.: a new giant freshwater foraminifer, with remarks on the taxon Reticulomyxidae (emend.).

Reticulomyxids are organotrophic freshwater foraminifers typically placed within the radiation of early monothalamous Foraminifera. Though ubiquitous, reticulomyxids are rarely reported, which may be due both to their concealed life style and to inappropriate isolation techniques. Their taxonomic position is largely based on developmental stages of the life cycle. Here, we describe a new freshwater species, Dracomyxa pallida gen. nov. et sp. nov., isolated from submersed plant material. It has two possible life cycles including small cells, large plasmodia and encysted stages. Both types of development occur simultaneously in cultures derived from a single cell as well as in crude cultures. We amplified and sequenced a short sequence fragment of the 18S rRNA gene of the new isolate. Comparative phylogenetic analysis and molecular characterization indicate that it is a new reticulomyxid species, with Reticulomyxa filosa Nauss, Haplomyxa saranae Dellinger and Wobo gigas Hülsmann as the closest relatives. Unique features such as tripodal pediculated cysts and the lack of cleansing process justify the erection of a new genus.

The genome of the foraminiferan Reticulomyxa filosa.

BACKGROUND: Rhizaria are a major branch of eukaryote evolution with an extensive microfossil record, but only scarce molecular data are available. The rhizarian species Reticulomyxa filosa, belonging to the Foraminifera, is free-living in freshwater environments. In culture, it thrives only as a plasmodium with thousands of haploid nuclei in one cell. The R. filosa genome is the first foraminiferal genome to be deciphered. RESULTS: The genome is extremely repetitive, and the large amounts of identical sequences hint at frequent amplifications and homologous recombination events. Presumably, these mechanisms are employed to provide more gene copies for higher transcriptional activity and to build up a reservoir of gene diversification in certain gene families, such as the kinesin family. The gene repertoire indicates that it is able to switch to a single-celled, flagellated sexual state never observed in culture. Comparison to another rhizarian, the chlorarachniophyte alga Bigelowiella natans, reveals that proteins involved in signaling were likely drivers in establishing the Rhizaria lineage. Compared to some other protists, horizontal gene transfer is limited, but we found evidence of bacterial-to-eukaryote and eukaryote-to-eukaryote transfer events. CONCLUSIONS: The R. filosa genome exhibits a unique architecture with extensive repeat homogenization and gene amplification, which highlights its potential for diverse life-cycle stages. The ability of R. filosa to rapidly transport matter from the pseudopodia to the cell body may be supported by the high diversification of actin and kinesin gene family members.

Ernst Haeckel's discovery of Magosphaera planula: a vestige of metazoan origins?

In September of 1869, while studying sponges off the Norwegian island of Gisoe, Ernst Haeckel (1834-1919) discovered a tiny, flagellated ball-shaped organism swimming about in his samples. Appearing first to be the planula larva of an invertebrate marine animal further observation revealed it to be a colony of flagellated cells with a complex life cycle transitioning between multicellular and single-cell stages and several distinct forms of protozoa. Haeckel named it Magosphaera planula (the "magician's ball") and it eventually assumed a central role in his theories of animal evolution, appearing as the modern exemplar of the blastaea stage in his gastraea theory of metazoan evolution. Throughout the latter half of the nineteenth century and into the twentieth it was an object of considerable scientific interest, and yet it was only ever observed by Haeckel himself and then only the once. Eventually it faded altogether from scientific discussion. This paper traces the rise and fall of Magosphaera as an important epistemic object in the theories of Haeckel and other biologists, and an attempt is made to identify what exactly the organism (or organisms!) was that Haeckel observed in the fall of 1869.