Sea Star Updates

In my last blog post, I spoke a bit about the developing Henricia that Dr. Allen and I have been working with. I am studying this large-egged brooding sea star to investigate the effects of reduced maternal investment. Since he had not worked with this species before, we decided to only observe this first set of embryos since the timeline for their development is still unclear. For my actual experimental data, I am planning to ablate one cell of the developing embryos once it gets to the two cell stage. However, the window of time that an egg spends in the two cell stage is small, so acutely understanding their development is necessary for the actual experiment.

As of now, the lone juvenile from the clutch that Dr. Allen spawned a few weeks ago is doing pretty well! It has been approximately eight weeks since he was born and now he is an active little sea star. Henricia are macroscopic throughout the entirety of their development and right now the juvenile is about two or three millimeters long. It has completed metamorphosis, meaning that it has developed pentaradial symmetry and tube feet. In contrast, sea star larvae have bilateral symmetry and no tube feet. They also have ciliated bands around the perimeter of their bodies, which they use to direct food toward their mouths. However, the Henricia do not feed until they are adults, since their mother provides them with so much nutrition in the eggs, which is another reason why this study organism piqued my interest.

The larvae that are about six weeks old have also been faring well. Unfortunately, I did not realize that the lack of fresh water would cause the eggs in the pyrex bowls to die, but once I started changing their water regularly, half of them managed to survive and are thriving. The embryos in the bowls are approximately at the same stage of development, but the embryos in the tea boys are not uniform in their growth. Some are still somewhat egg-like shaped, whereas others are developing lobes. The strangest finding is that some of the eggs in the tea boys are smaller than when they were first hatched. I have not quantified this yet, but they are especially notable when all the larvae in the bowl are already in the earlier stages of development. Dr. Allen suggested that they could be eggs that never developed but have not popped yet, but we are very unsure of what they are. This unexpected finding is very interesting and I can’t wait to see how the embryos continue to grow. If you wanted to see pictures of the developing sea stars, check out the Allen Lab’s Instagram page @larvaerock