Amphicutis stygobita dorsal (aboral) SEMs A disk with fenestrated scales, 1st 2 arm segments, Vs with lateral extensions B 1st arm segment, ventral muscle flange extends past dorsal muscle flange C 1st arm segment, middle of LAPs curve inward to meet 3-4 vertebral extensions D 1st arm segment, dorsal arm plate, LAP with 2 spines E LAP with 2 fenestrated spines F LAP with 2 spine articulations. Abbreviations: DAP – dorsal arm plate, DMF – dorsal muscle flange, LAP – lateral arm plate, PB – podian basin, S – spine, SA – spine articulation, SL – suture line, V – vertebra, VAP – ventral arm plate, VE – vertebral extension, VMF - ventral muscle flange.