Development of pedicellariae in the pluteus larva of Lytechinus pictus (Echinodermata: Echinoidea)

Abstract

Three tridentate pedicellariae develop in the pluteus larva of Lytechinus pictus. Two are located on the right side of the larval body and the third is on the posterior end of the larva. The pedicellariae form from mesenchyme associated with the larval skeleton which becomes enclosed in an invagination of larval epidermis. The mesenchyme within the pedicellaria primordium aggregates into groups of cells that become skeletogenic tissues which secrete the pedicellaria jaws, and smooth and striated muscles. Nerves and sensory cells develop within the epidermis covering the pedicellariae. Pedicellaria formation takes 3 days and occurs about midway through the development of the adult rudiment. During metamorphosis the pedicellariae are shifted to the aboral surface of the juvenile.Pedicellariae that develop in the larvae are fully operable prior to metamorphosis and do not appear to be released from any rudimentary state of development by metamorphosis. At least 16 echinoid species are reported to form pedicellariae in the larva. The precocious development of these adult structures appears to be dispersed throughout the orders of regular urchins.