Larval and life-cycle patterns in echinoderms

We review the literature on larval development of 182 asteroids, 20 crinoid s, 177 echinoids, 69 holothuroids, and 67 ophiuroids. For each class, we de scribe the various larval types, common features of a larval body plan, dev elopmental patterns in terms of life-cycle character states and sequences o f larval stages, phylogenetic distribution of these traits, and infer evolu tionary transitions that account for the documented diversity. Asteroids, e chinoids, holothuroids, and ophiuroids, but not crinoids, have feeding larv ae. All five classes have evolved nonfeeding larvae. Direct development has been documented in asteroids, echinoids, and ophiuroids. Facultative plank totrophy has been documented only in echinoids. It is surprising that benth ic, free-living, feeding larvae have not been reported in echinoderms. From this review, we conclude that it is the ecological and functional demands on larvae which impose limits on developmental evolution and determine the associations of larval types and life-cycle character states that give rise to the developmental patterns that we observe in echinoderms. Two factors seriously limit analyses of larval and life-cycle evolution in echinoderms. First is the limited understanding of developmental diversity and second i s the lack of good phylogenies.