<i>Meteora sporadica</i> , a protist with incredible cell architecture, is related to Hemimastigophora
Bibliographic record
Abstract
Summary ‘Kingdom-level’ branches are being added to the tree of eukaryotes at a rate approaching one per year, with no signs of slowing down 1–4 . Some are completely new discoveries, while others are morphologically unusual protists that were previously described but lacked molecular data. For example, Hemimastigophora are predatory protists with two rows of flagella that were known since the 19 th century, but proved to represent a new deep-branching eukaryote lineage when phylogenomic analyses were conducted 2 . Meteora sporadica Hausmann et al. 2002 5 is a protist with a unique morphology and motility; cells glide over substrates along a long axis of anterior and posterior projections, and have a pair of lateral ‘arms’ that swing back and forth. Originally, Meteora was described by light microscopy only, from a short-term enrichment of deep-sea sediment. A small subunit ribosomal RNA (SSU rRNA) sequence was reported recently, but the phylogenetic placement of Meteora remained unresolved 6 . Here, we investigated two cultivated Meteora sporadica isolates in detail. Transmission electron microscopy showed that the anterior-posterior projections are supported by microtubules originating from a cluster of subnuclear MTOCs. Likewise, the arms are supported by microtubules, and neither have a flagellar axoneme-like structure. Sequencing the mitochondrial genome showed this to be amongst the most gene-rich known, outside jakobids. Remarkably, phylogenomic analyses of 254 nuclear protein-coding genes robustly support a close relationship with Hemimastigophora. Our study suggests that Meteora and Hemimastigophora together represent a morphologically diverse ‘supergroup’, and thus are important for resolving the tree of eukaryote life and early eukaryote evolution.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".