Fig. 5: Morphological comparisons of extant and fossil black coral endoskeletons.

a–f Extant black corals with characteristic internal multi-layered concentrical structures. a–c Antipathidae, Stichopathes spinosa; d–f Antipathidae, Antipathes sarothrum. g–u Three fossil species of the family Sterictopathidae fam. nov.: g–i Sterictopathes sp. encrusting an interior tube of another Cnidaria Sphenothallus sp. with three characteristic internal septa (white arrows); j–o Sterictopathes seira sp. nov. with internal multi-layered concentrical structure of itself (j–l) or encrusting the tube of Sphenothallus sp; m–o with ten characteristic internal septa (white arrows); p–u Sterictopathes radicatus encrusting two interior tubes of Sphenothallus sp., only one tube (p–r) with four internal septa (white arrows). Specimens: a–c ZSM20030289, d–f ZSM20030284, g–i ELI-FJG04013, j–l ELI-FJG03118, m–o ELI-FJG02302, p–r ELI-HHC031, s–u ELI-HHC051. Abbreviations: BR branch, CG circular gap, CC central canal, IS irregular space, MC multi-layered concentrical structure, RI ridge, SE septa, SP spine, SPH Sphenothallus, STP Sterictopathes sp, STR Sterictopathes radicatus, STS Sterictopathes seira. Scale bars: a–u = 150 μm. The 3D construction data of the extant species Leiopathes bullosa (Leiopathidae) is available form Morphobank (accession number: M894365-M894377).