Development in <i>Berthella californica</i> (Gastropoda: Opisthobranchia) with comparative observations on phylogenetically relevant larval characters among nudipleuran opisthobranchs
Why this work is in the frame
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Bibliographic record
Abstract
Abstract. Morphological criteria defining the Nudipleura and sister group relationships among the three nudipleuran subgroups (pleurobranchoideans, anthobranch nudibranchs, and cladobranch nudibranchs) have been controversial. Analysis of larval stages may help resolve these uncertainties by identifying additional phylogenetically informative characters, but existing information on pleurobranchoidean larvae is meager. We studied larval development and metamorphosis of the pleurobranchoidean Berthella californica using histological sections, scanning and transmission electron microscopy, and immunolabeling of neurons within the larval apical ganglion. We also provide comparative data on other nudipleuran larvae that may be useful for phylogenetic reconstruction. Berthella californica fills a previously unoccupied place within an evolutionary scenario that derives nudibranchs from pleurobranchoideans, two groups in which the larval mantle fold forms the post‐metamorphic notum (dorsal epidermis). In B. californica , reflection of the mantle fold epithelium to form the notum begins at metamorphosis, as also occurs in nudibranchs, whereas mantle reflection in other pleurobranchoideans begins well before metamorphosis. Dissolution of overgrown shell walls inside the protoconch and formation of the post‐metamorphic notum from the inner epithelium of the larval mantle fold may be synapomorphies of the Nudipleura. The larval shell in B. californica is additionally noteworthy because it acquires bilateral symmetry later in development, which is very unusual among larval opisthobranchs. We demonstrate an osphradium in the larvae of two pleurobranchoideans and one anthobranch nudibranch, although adults lack this trait. We also identified an autapomorphy of cladobranch nudibranchs in the form of five ampullary neurons within the larval apical ganglion, whereas other planktotrophic opisthobranch larvae have only four of these neurons. Although our data provide morphological criteria defining both the Nudipleura and the cladobranch nudibranchs, they are insufficient to resolve sister group relationships within the Nudipleura.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 it