. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. + auricles Figure 10. Echinoid phylogeny. The three possible phylogenetic relationships between cidaroids, echi- nothurioids, and nonechinothurioid euechinoids are shown. The states of two characters are noted in each case: presence of a vestibule during metamorphosis and the nature of lantern supports. Here we assume that the ancestor of post-Paleozoic echmoids lacked a vestibule and possessed cidaroid-type lantern supports. Acquisition of a vestibule and of lantern supports attached to ambulacral rows (euechinoid-type) are
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. + auricles Figure 10. Echinoid phylogeny. The three possible phylogenetic relationships between cidaroids, echi- nothurioids, and nonechinothurioid euechinoids are shown. The states of two characters are noted in each case: presence of a vestibule during metamorphosis and the nature of lantern supports. Here we assume that the ancestor of post-Paleozoic echmoids lacked a vestibule and possessed cidaroid-type lantern supports. Acquisition of a vestibule and of lantern supports attached to ambulacral rows (euechinoid-type) are indi- cated "+ vestibule" and "+ auricles," respectively. The most parsimonious phylogenetic hypothesis is represented by cladogram a; cladograms b and c require more changes and parallel evolution of auricles. This hypothesis is supported by additional morphological and molecular data (see text). vestibule + auricles evolution of auricles, which are complex morphological characters (Fig. lOb, c). Although they differ in details, the pluteus larvae of cidaroids and euechinoids are sufficiently similar that the pluteus is likely a primitive feature of post-Paleozoic echinoids. Therefore, the ex- tinct common ancestor to cidaroids and euechinoids probably developed via a pluteus larva and lacked a ves- tibule. A vestibule was probably acquired after echino- thurioids split from the remaining euechinoid orders, during early radiation of the euechinoids. P. parvispinns illustrates the diversity of developmen- tal patterns exhibited by echinoids. The lack of a vesti- bule, more simple metamorphosis, and the slower rate of development than comparable euechinoids are features common to cidaroids. Other characteristics such as large gametes, the absence of micromeres, a wrinkled blastula, altered msp!30 expression, and accelerated echinus ru- diment formation appear to be associated with the evolu- tion of lecithotrophic development. The ability to differentiate be
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
