The best-laid planulae

I have a small side project in which I'm trying (slowly) to learn and document the local hydroids.  I was photographing a common species this week — Eudendrium californicum — because it's noticeably reproductive at this time of year.

These wonderful colonial marine invertebrates are often visible in the low intertidal zone on rocky shores.  They appear plant-like at first, but remember that they're related to sea anemones (and jellyfish and corals).  Those flower-like units have tiny mouths surrounded by stinging tentacles waiting for prey to swim by too closely.

 

The bright orange clusters in the background are reproductive units.  I zoomed in on one cluster to take a picture and my eyes opened wide when I realized that a larva was hatching at that very moment!

In this species, the fertilized eggs are retained in these clusters and they develop into planula larvae that look like small, pink tear-drop shaped worms (but they're not worms!).  The planulae hatch and are free swimming for a short time before settling onto the bottom and undergoing metamorphosis into new hydroid polyps that will continue developing into larger, branched colonies like the one you see in the image above.

It didn't take very long for this planula larva to hatch, so today you (yes, you!) get to see this process in pictures.

 

For orientation, most of the developing embryos are orange.  There's one blob that's more pinkish in color near the center of the image (it's also slightly smaller).  That's the one you're going to watch through this series of pictures.  If you look carefully, you'll see that it's emerging from a clear capsule.  In the picture above, the pink larva is half outside and half inside the capsule.  Okay, here you go:

 

 

 

 

 

Fun, right?  

One more image, pulled back a little, that shows the entire hydroid polyp with a large cluster of developing embryos, and the newly hatched planula larva swimming away.  Good luck, little one!