Evolution of pelagic direct development in the starfish Pteraster tesselatus (Asteroidea: Velatida)

摘要: Abstract Despite a diversity of larval forms, remarkably conservative features asteroid development define body plan that occurs throughout the class. However, recent work on starfish Pleraster tesselatus has documented highly derived pattern development. Several features, including radial symmetry, parallel embryonic and adult axes absence preoral lobe, formation coeloms in orientation from seven separate enterocoels, have not been reported asteroids before. The complete are found other asteroids, indicates P. develops directly embryo to juvenille pelagic, nonfeeding (lecithotrophic), but nonlarval mode I postulate direct evolved over an extended period lineage brooding, deep-sea velatid (probably pterasterid) ancestors . Selection for increased developmental efficiency (loss nonfunctional features) brooded offspring, could explain lack settlement structures, arrangement coeloms, transverse juvenile disc, bilateral symmetry. coelomogenesis velatids (e.g. solasterids) by relatively simple changes timing enterocoel formation. Rotation posterior translation coelomic fate map archenteron prior would produce compartments characterizes These unusual lead radically different interpretation evolution pelagic ‘larva’ : (1) benthic (2) extreme simplification involving loss all life cycle, (3) subsequent re-evolution In case , where structures were lost, there do seem be functional constraints preventing Analysis larvae, suggests major ecological transitions histories need associated with substantial morphology. should occurred repeatedly readily reversible. findings interesting implications dispersal marine invertebrates.