Metamorphosed juvenile of Strongylocentrotus purpuratus

These pictures show a newly metamorphosed juvenile of the purple sea urchin Strongylocentrotus  purpuratus, a common intertidal organism in Oregon.  Take note of the red pigment granules and the green coloration of the internal structure though the transparent skeletal plates.  Purple urchin pluteus larvae swim and feed in the plankton for several weeks prior to settlement on the seabed and metamorphosis into the juvenile stage. This particular specimen was cultured in the lab from gametes collected from induced spawning via injection of adults with a KCl solution and fertilized in vitro on April 3, 2012.  Like the adults, the juveniles of this species are benthic feeders and have acquired traits adapted to their environment, for example, tube feet, and juvenile (splayed) and adult (pointed) spines.  At this early stage, the juvenile possesses four adult spines per interambulacrum, two juvenile spines, a single  unpaired primary podium per ambulacrum, and five to eight additional juvenile spines located on the aboral surface (Miller and Emlet, 1999).  The juvenile spines are four-pronged, shorter, and located more orally compared to the longer, barbed adult spines.

The second image is a close up of the oral surface of the juvenile, showing the five tube feet and the transparent skeletal plates.  After settlement, the juvenile is not able to feed for 5 to 6 days due to an incomplete gut.  

Leahy, PS.  1986.  Laboratory culture of Strongylocentrotus purpuratus adults, embryos, and larvae.  Methods in Cell Biology, 27, 1-12.         

Miller, BA., and Emlet RB.  1999.  Development of newly metamorphosed juvenile sea urchins (Strongylocentrotus franciscanus and S. purpuratus): morphology, the effects of temperature and larval food ration, and a method for determining age.  Journal of Experimental Marine Biology and Ecology. 235(1): 67-90.