Fertilization in the white chiton, Stenosemus albus, with implications for its phylogenetic position
Bibliographic record
Abstract
Gamete structure and fertilization biology of the white chiton, Stenosemus albus (L., 1767), were studied with light and electron microscopy. Sperm structure was found to be similar to other Chitonina, but acrosomes are homogeneous in this species, like those of Chaetopleura apiculata (Say in Conrad, 1834). The egg of S. albus is covered by long spines with hooked tips. The bases of spines are perforated along their perimeters by a series of pores that provide sperm with direct access to the vitelline layer. This feature appears to be plesiomorphic and characterizes also Chaetopleura but not most Chitonina, which have a continuous dense layer overlying the hull. Beneath the vitelline layer, the egg membrane is formed into a series of cups with raised edges elaborated into microvilli that coincide with the bases of hull spines. Free-spawned sperm of S. albus were able to find the egg and penetrate a pore in the hull within 20 s. Evidence presented here, and previously, indicates that S. albus shares a number of key characters in common with Callochitonidae, which is a basal family within Chitonida. Taken together, the evidence suggests that Stenosemus belongs to a basal taxon within Chitonina, outside the Ischnochitoninae, in which it is currently placed.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| 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".