This interactive tree diagram visualizes the hierarchical classification of fish species, from cartilaginous fish like sharks and rays to bony fish including ray-finned and lobe-finned varieties. Using D3 version 3.5’s `d3.layout.tree` and `d3.svg.diagonal`, the visualization renders an SVG with animated transitions. Clicking nodes collapses or expands subtrees, with circles changing color from teal to lightsteelblue to indicate collapsed states. The data is hardcoded as a JSON array in the script, with node positions calculated based on depth and screen margins.