Fig. 5

a–d Hymenaster membranaceus Sladen, 1889. a, b Ambulacral ossicles, interior a and exterior b aspects. c Ambulacral ossicle. d Drawing of in situ adambulacral spines. ada1, ada2-3, adambulacral articulations: adadm, interadambulacral muscle. als, actinolateral spine. ads, adambulacral spines. ap, aperture. aps, apertural spine. Porcupine Basin, North Atlantic. e, f Asterina gibbosa Pennant, 1777, Recent, North Sea, United Kingdom. E, abactinal view dissected to show interior. b Actinal view (after Gale 2011a, pl. 1/3, 4). Note short arms, broad interradii, imbricating actinal and abactinal ossicles. G, reconstructed adambulacrals 1–5 of Thuyaster fontenoillensis gen. nov., sp. nov., based on ossicles illustrated in Fig. 14. h Drawing of actinal interradius of Korethraster hispidus. I, actinal interradius of Protremaster uniserialis, from the Lower Jurassic of Antarctica. Note the three rows of attachment sites for large spines on the adambulacrals (1–3). h, i After Gale (2011a, text-fig. 25b, c). Note progressive increase in size of adambulacrals distally from oral contact. j–l Muscularisation of abactinal ossicles in pterasterids. j Shows interabactinal muscle in green, which when contracted, reduces the coelomic volume, causing the papulae to swell. k Primary interradial of Savignaster wardi to show insertion site of abactinal muscle (fine stereom) (original of Gale 2011a, pl. 25, Fig. 14; NHMUK EE XXXXXX). Equivalent view of primary interradial of Pteraster corynetes. Scale bars in a–c, k, l equal 0.5 mm, in e, f equal 10 mm