Development of the Eggs and Larvae of the Slender Mola, Ranzania Laevis (Pisces, Molidae)

The development of Ranzania laevis is described and illustrated from eggs and larvae collected in Hawaiian waters. Eggs were reared in the laboratory. The eggs are spherical, 1.42-1.66 mm in diameter, possess 20-30 oil droplets and hatch in 7 to 8 days. The newly hatched larvae lack body spines but develop them within 2 days. The spines grow rapidly and reach maximal development at about the time of ossification of the medial fin rays and are then either resorbed or shed. Young larvae have a well developed notochord, finfold, and post-anal myomeres; these atrophy during development. The clavus (pseudocaudal) rays form starting from the terminus of the dorsal and anal fins and close the gap inward. An ossified caudal complex homologous to that of more typical teleosts does not form. The eggs can be distinguished from all others in Hawaiian waters by size, oil droplets, and pigmentation. The larvae can be distinguished by shape, pigmentation, and later by spination. The apparent spawning season in Hawaii extends from January through early May. Both eggs and larvae are more abundant along northern coasts than along southern coasts of the Hawaiian Islands studied.