Juvenile Seastars

Even though I am now home from Friday Harbor, I need to tell you all about my last weeks at the labs and all of my research.  The last time I updated you on my research I was trying to spawn and raise Pteraster embryos to hatch. Unfortunately, not enough Pteraster hatched to run any experiments, but we did have 4 embryos reach metamorphosis and become juveniles. This was extremely exciting, even though there were only 4 because I had never worked with Pteraster before, and it is extremely encouraging for future experiments that I am able to rear the embryos to metamorphosis once they hatch.

While the Pteraster experiment never came to fruition, my experiments with the Pisaster were still running and were extremely promising. 30 days after the Pisaster hatched, they began settling and going through metamorphosis. This is extremely quick for Pisaster, as they usually take over 40 days to reach metamorphosis. In order to encourage the larvae to settle, I placed a mussel shell in each beaker containing larvae to provide a cue to induce settlement. After the Pisaster larvae settled, I isolated them from the beakers, then measured their disk diameter and counted the number of spines. I also took pictures of the juveniles under polarized light to show the skeletal elements so I can quantify the skeleton at a later point. When I get back to school, I will measure all of the juveniles again to see if they have grown as well as compare the growth rates of the half sized larvae to that of the whole sized larvae. Below are some pictures of the larvae and juveniles that I reared.

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A larva in the process of metamorphosis, with the juvenile rudiment visible on the bottom of the larva.

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A juvenile Pisaster after metamorphosis


Pisaster juvenile lit under polarized light, with skeletal elements illuminated


A late stage larva with a well developed juvenile rudiment on the left.


  1. Hi Allen, how are the sea stars developing? I was wondering in what settings you hatched the sea stars? I know that warmer waters or salinity changes may have some effect on embryonic development. Do you think your hatching process may have had some effect on the development of the sea stars or was your hatching very controlled and as close to wild conditions as possible? Thanks and I hope it’s all going well!