Fig. 2

Molecular characterization of juvenile P. lividus cell and tissue types. a Staining with antibodies against Msp130 and β-tubulin reveals the distribution of musculature. Details in text. b Staining against Msp130 and MHC shows MHC⁺ cells within the spines. c Staining against ELAV and Msp130 shows nerves in the secondary podia, and skeletogenic cells in the spines. d Staining for synaptotagmin and serotonin reveals the extent of the nervous system and serotonergic neurons. e–h Immunostaining using antibodies against the skeletogenic proteins Sm30 and Sm50 stains skeletal tissues, with stronger staining in more recently deposited biomineral. i–l Localization of the skeletogenic proteins Msp130 (green) and Sm50 (purple) in a J1 P. lividus juvenile. Description of stainings given in the main text. js, juvenile spine; ps primary interambulacral spine; ped, pedicellariae; aps, ambulacral primary spine; pp, primary podia; sp, secondary podia; tub, tubercle; gut, gut; op, ocular plate, gp, genital plate; ap, anal plate; sph, sphaeridia; al, Aristotle’s lantern. Scale bars in a, c, e are 100 μm; d is 50 μm; b, f, h are 25 μm, and g, and i–l are 200 μm