Ossicle change in Holothuria scabra with a discussion of ossicle evolutionwithin the Holothuriidae (Echinodermata)

Ossicles of Holothuria (Metriatyla) scabra Jaeger, 1833 vary mainly in earl y juveniles between 0.9 and 15 mm long. While ossicles were not observed in auricularia and doliolaria larvae, which instead possessed elastic balls, ossicles were present in late pentactulae. Specimens 0.9-1.5 mm long have t ables with tall spire (4-5 cross beams), no buttons, and large irregular pe rforated plates. Specimens 5-6 mm long have tables with moderate spire (2-4 cross beams) and a few smooth buttons. Specimens 9-16 mm long have tables with low spire (1-2 cross beams) and knobbed buttons. From 30 mm, ossicle a re similar to those of adults, with more buttons and fewer tables. Several features of the ossicles of early juveniles, including their size, shape an d prevalence, are unique to the species. Comparison with holothurian juveni les of other species indicates that presence of tables with tall spire and absence of buttons are plesiomorph characters in the evolution of the Holot huriidae.