Sensory Systems in Amphioxus: A Window on the Ancestral Chordate Condition
Bibliographic record
Abstract
Amphioxus has an assortment of cells and organs for sensing light and mechanical stimuli. Vertebrate counterparts of these structures are not always apparent, and a strong case can be made for homology in only a few instances. For example, amphioxus has anatomically simple but plausible homologs of both the pineal and paired eyes of vertebrates. Placodal and neural crest derivatives are, however, more problematic: the evidence for an olfactory system in amphioxus is only circumstantial and, despite the variety of secondary sensory cell types that occur on the body surface in amphioxus, none are obvious homologs of vertebrate taste buds, neuromasts or acoustic hair cells. A useful perspective can nevertheless be gained by examining differences in amphioxus and vertebrate development, specifically how each specifies and positions sensory precursors, controls their proliferation, and deploys them through the body. The much larger size of vertebrate embryos and the need to cope developmentally with increased scale and cell numbers may account for some key vertebrate innovations, including placodes and neural crest. The presence or absence of specific structural adaptations, like the latter, is therefore less useful for judging homology between amphioxus and vertebrates than shared features of specific cell types. It is also clear that the duration of embryogenesis in vertebrates has been significantly extended in comparison with ancestral chordates so as to incorporate events that would originally have occurred during the post-embryonic growth period, including events of neurogenesis. Consequently, no scenario for the origin of vertebrates can be considered complete unless it deals explicitly with the whole of the life history and changes to it.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".