Scanning electron micrographs (SEM) of central region of dorsal arm plates (DAP) of Ophionereis brittle stars. SEM of a DAP from mature Ophionereis commutabilis (a) and O. reticulata (b). SEM of a DAP of juvenile O. reticulata (c). SEM of a cross-section of a fractured DAP from mature O. commutabilis (d) and O. reticulata (e). Orientation (do: dorsal, v: ventral). Scale bars: 50 μm (a–c); 100 μm (d–e).