Gills are not used for gas exchange in the suspension-feeding hemichordate <i>Protoglossus graveolens</i>
Bibliographic record
Abstract
Abstract The gills are hypothesized to play a key role in early vertebrate evolution by replacing the skin as the primary site of gas exchange. In this scenario, water flow across the gills used for suspension feeding in ancestral deuterostomes was coopted for breathing in stem vertebrates to facilitate the evolution of larger, active fishes. This hypothesis is supported by a stem-vertebrate origin for structures that increase gill capacity for breathing. However, these structures might have instead enhanced an already dominant capacity at the gills of invertebrate deuterostomes rather than mark a shift from the skin. To test this, we characterized gill function for gas exchange in the suspension-feeding hemichordate acorn worm Protoglossus graveolens . We measured oxygen uptake and ammonia excretion in whole worms and worm halves with or without gills at 10°C and during an acute thermal challenge at 20°C to maximize gill recruitment. Gills did not enhance oxygen uptake or ammonia excretion, suggesting they are not a primary site of gas exchange. This is the first test of gill function for gas exchange in a suspension-feeding invertebrate deuterostome, and it provides essential support for the long-hypothesized vertebrate origin of breathing at gills and its role in early vertebrate 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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".