The Leg Depressor and Levator Muscles in the Squat Lobster <i>Munida quadrispina</i> (Galatheidae) and the Crayfish <i>Procambarus clarkii</i> (Astacidae) Have Multiple Heads with Potentially Different Functions
Bibliographic record
Abstract
The proximal leg muscles of decapod crustaceans, controlling movements at the first two joints, are anatomically more complex than the better-studied distal leg muscles. Despite extensive research on their involvement in diverse behaviors, no complete descriptions of the anatomy and innervation of these muscles for any species have been published. We describe the anatomy and innervation of the depressor muscle in the second leg of the squat lobster Munida quadrispina and compare its anatomy with that of its homologue in the crayfish Procambarus clarkii and its antagonist, the levator, in both species. Of the six anatomically distinct heads comprising M. quadrispina's depressor muscle, one arises in the coxa (coxal head) and five are bi-articular (cross two joints), arising from widely dispersed sites on the thoracic endophragmal skeleton (dorsal, sternal, caudal, ventral-rostral, ventral-caudal heads). The heads' widely divergent force vectors are accommodated by the depressor apodeme's bifurcation at a thin flexible point. In total, eighteen neurons with central somata were backfilled from nerve branches to the heads. The common inhibitor and at least one neuron of unknown function with rostro-lateral soma and extremely sparse neurites innervate all heads. The sixteen excitatory motoneurons' somata are clustered in two locations, five rostral and eleven caudal to the neuropil. Rostral motoneurons innervate the two ventral heads (rostral and caudal). Their integrating segments lie rostral to those of the caudal group motoneurons and are straight or 'Y'-shaped, the latter longer and larger in diameter. Both morphological types have one prominent medial neurite that crosses the midline and could allow direct interaction between bilateral pairs of rostral motoneurons. The caudal motoneurons provide partially shared innervation to the remaining four heads. Six provide exclusive innervation, one to the caudal head, two to the sternal head, and three to the bi-articular dorsal head and uni-articular coxal head which share innervation. Of the remaining five caudal motoneurons, two are shared by the caudal head and the dorsal-coxal pair of heads and three are shared by the caudal and sternal heads. P. clarkii has two depressor muscles; the rostral depressor has a single head morphologically similar to the ventral rostral head in M. quadrispina; the caudal depressor muscle has four heads (dorsal, coxal, caudal, sternal) that insert on the large caudal depressor apodeme. The overall organization of depressor muscle heads in P. clarkii and M. quadrispina is similar, taking into consideration the different internal and external thoracic anatomies and the different resting stances, horizontal and tilted, respectively. As in other species, M. quadrispina and P. clarkii have two levator muscles, each with an apodeme of complex structure attributable to the levators' role in leg autotomy. The caudal levator arises in the coxa; it has two heads in M. quadrispina, but only one in P. clarkii. In both species the rostral levator has three heads all arising within the thorax. Divergent force vectors and partially independent innervation of different heads composing complex musculature at single joints constitute an anatomical level of organization that neural mechanisms must accommodate to produce adaptive movements.
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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".