Multiple functions of ion transport by the nuchal organ in embryos and neonates of the freshwater branchiopod crustacean, <i>Daphnia magna</i>
Bibliographic record
Abstract
The nuchal organ, also referred to as the dorsal organ or neck organ, is a dorsal structure located posteriorly to the compound eye, between the bases of the second antennae of embryonic and neonate branchiopod crustaceans such as the ‘water flea’, Daphnia magna. The ultrastructure of the nuchal organ is similar to ion-transporting tissues in other crustaceans, including abundant mitochondria and extensive amplification of apical and basal plasma membranes through microvilli and infoldings, but direct evidence for ion transport is lacking. We have used the Scanning Ion-selective Electrode Technique to measure transport of Na+, K+, H+, Cl−, NH4+ and Ca2+ across the nuchal organ and body surface of embryos and neonates bathed in dechlorinated Hamilton tap water. Influx of Na+ and efflux of H+ and NH4+ were measured across the nuchal organ of both embryos and neonates. We propose that the efflux of K+ and Cl− across the nuchal organ in embryos is related to the expansion of the haemocoel and release of intracellular solutes into the extracellular space during development. K+ is taken up across the nuchal organ later during development, coincident with expansion of the intracellular compartment through development of gills and other organs. Ca2+ influx across the nuchal organ and body surface of neonates but not embryos is presumably related to calcification of the exoskeleton. Increases in the levels of Na+ and Ca2+ in the water within the brood chamber suggests maternal provisioning of ions for uptake by the embryos. Our data thus support roles of the nuchal organ in ionoregulation, pH regulation, and nitrogenous waste excretion.
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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) | 0.000 | 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".