Embryonic, Larval, and Juvenile Development of the Sea Biscuit Clypeaster subdepressus (Echinodermata: Clypeasteroida)

• Grant number: 10/01729-6
• Support Opportunities: Regular Research Grants - Publications - Scientific article
• Start date: May 01, 2010
• End date: October 31, 2010
• Field of knowledge: Biological Sciences - Zoology - Morphology of Recent Groups
• Principal Investigator: Alvaro Esteves Migotto
• Grantee: Alvaro Esteves Migotto
• Host Institution: Centro de Biologia Marinha (CEBIMAR). Universidade de São Paulo (USP). São Sebastião , SP, Brazil

Abstract

Sea biscuits and sand dollars diverged from other irregular echinoids approximately 55 million years ago and rapidly dispersed to oceans worldwide. A series of morphological changes were associated with the occupation of sand beds such as attening of the body, shortening of primary spines, multiplication of podia, and retention of the lantern of Aristotle into adulthood. To investigate the developmental basis of such morphological changes we documented the ontogeny of Clypeaster subdepressus. We obtained gametes from adult specimens by KCl injection and raised the embryos at 26 _C. Ciliated blastulae hatched 7.5 h after sperm entry. During gastrulation the archenteron elongated continuously while ectodermal red-pigmented cells migrated synchronously to the apical plate. Pluteus larvae began to feed in 3 d and were _20 d old at metamorphosis; starved larvae died 17 d after fertilization. Postlarval juveniles had neither mouth nor anus nor plates on the aboral side, except for the remnants of larval spicules, but their bilateral symmetry became evident after the resorption of larval tissues. Ossicles of the lantern were present and organized in 5 groups. Each group had 1 tooth, 2 demipyramids, and 2 epiphyses with a rotula in between. Early appendages consisted of 15 spines, 15 podia (2 types), and 5 sphaeridia. Podial types were distributed in accordance to Lov_en's rule and the _rst podium of each ambulacrum was not encircled by the skeleton. Seven days after metamorphosis juveniles began to feed Development of C. subdepressus 2 by rasping sand grains with the lantern. Juveniles survived in laboratory cultures for _9 months and died with < 500 _m wide, a single open sphaeridium per ambulacrum, aboral anus, and no di_erentiated food grooves or petaloids. Tracking the morphogenesis of early juveniles is a necessary step to elucidate the developmental mechanisms of echinoid growth and important groundwork to clarify homologies between irregular urchins. (AU)