Amphicutis stygobita SEMs of vertebrae (Vs) A V from mid-section of arm with lateral extensions, length ~3 × width, dorsal view, distal down B V from distal area of arm, length ~6 × width, ventral view, distal left, bridge formed between ambulacrals C joint between 1st 2 Vs outside disk, dorsal, distal down D distal face of segment showing V enclosed by DAP, VAP, and 2 LAPs with spines E dorsal/proximal end view of V tilted ~40 degrees showing proximal end (up) with large dorsal muscle flanges and 2 articulating facets (top) F ventral view of V rotated to show distal end with dorsal and ventral muscle flanges, 2 articulating facets, and median process. Abbreviations as in Fig. 7 plus: AF- articulating facet, DP – dorsal process, MP – median process.