In 245 muscles from one Platynereis larva, input similarity and attachment axis alignment had correlation 0.099, with 0.090 expected under type, region and side controls

Do muscles with similar neural inputs have parallel attachment axes? We joined two maps from one three-day-old Platynereis dumerilii larva. We fitted axes to measured three-dimensional attachment sites. The main panel had 245 muscles of 31 types and 4,187 pairs of different types in the same region and on the same side. Neural input cosine and squared axis alignment had correlation 0.0991. Whole input profiles assigned at random within muscle type, region and side had exact expected correlation 0.0905. The excess was 0.0086; a two-sided test with 9,999 assignments gave p = 0.0858. Only 1,488 pair scores could change under this control. Added input partner count or position blocks left excesses of 0.0014 to 0.0038. A stricter geometry panel of 134 muscles had excess 0.0219 (p = 0.0060). Follow-up position controls reduced it to 0.0076 or 0.0035 and could change fewer scores. These comparisons do not isolate a causal effect of position. Attachment axes are a proxy for muscle orientation, input counts are sparse, and cell types used morphology and connectivity in their definitions. The data contain one animal. The contribution is a numerical axis atlas, conditional pair tests, figures, source provenance, code, an inspection tool and full repeat instructions.

Platynereis · connectome · muscle · desmosome · three-dimensional geometry · neural input · conditional permutation · reproducible analysis