This 2D companion looks straight down the division axis at the equatorial ring itself, modelled as 72 discrete actomyosin nodes spaced around the circumference — not a flattened copy of the 3D scene, but an independent particle-based mechanism. Each node i sits at a fixed angle and carries its own local ring radius ri(t), evolving under three real forces:
dr_i/dt = -(T/r_i - c_resist)/ξ (Laplace-type purse-string tension)
+ K·(r_{i-1} + r_{i+1} - 2r_i) (cortical coupling to neighbours)
+ noise_i(t) (stochastic myosin cluster jitter)
T = T0 · a_myosin · zoneGain(w) (narrower RhoA zone -> sharper pinch)
When every node shares the same radius the coupling term vanishes exactly and each node's equation collapses to the identical Laplace tension law f(R)=T/R used by the 3D simulator — verified numerically node-by-node. The coupling term is what makes this genuinely 2D: it lets individual myosin clusters pinch a little faster or slower than their neighbours, then relaxes that irregularity back into a smooth circle, exactly as a real actomyosin cortex resists local buckling. Watch the ring's outline instead of a single number — the puncta needn't stay perfectly synchronised while the ring as a whole still closes.
- Myosin-II activity — sets the per-node contractile tension T; higher activity drives faster, deeper constriction.
- Cortical resistance — membrane/cortex stiffness and cytoplasmic pressure opposing ingression; too high stalls the furrow.
- RhoA zone width — a wider active band spreads the same myosin pool more thinly (lower effective tension), producing a shallow, slow pinch instead of a sharp one.
- Ring irregularity — the spread (std/mean) of the 72 nodes' individual radii; a live measure of how far the ring currently is from a perfect circle.
- + Latrunculin — mimics an actin-polymerisation poison: myosin tension collapses and cortical elasticity relaxes every node back outward (regression), exactly as observed when cytokinesis drugs are added mid-division.