Oral examination

Anyone who went to graduate school in the sciences remembers what oral exams are like. I remember not having any fun at all in mine, and by the time I was dismissed I wasn't sure what my own name was. Fortunately, that is all ancient history and now I get to spend my time performing a different kind of oral examination on other creatures.

My oldest urchins are now 17 days post-metamorphosis and I've been watching them to see when their mouths break through. It seems to me that 17 days is a long time, but the time is near. Besides, the animal is always right. In the urchin that I examined closely the five teeth of Aristotle's lantern are very close to breaking through the thin membrane covering the mouth opening. The teeth are also much more active than they were a week earlier, as you can see in this short video clip:

I also checked out another tiny urchin and noticed that this individual has startlingly red buccal tube feet:

Juvenile sea urchin (Strongylocentrotus purpuratus), age 66 days, 27 March 2015. © Allison J. Gong
Juvenile sea urchin (Strongylocentrotus purpuratus), age 66 days. 27 March 2015.
© Allison J. Gong

Sea urchins have five pairs of large tube feet on the oral surface, surrounding the mouth. As with all tube feet, the buccal tube feet are part of the animal's water vascular system and are situated in the ambulacral region of the test; they are used to manipulate and grab food. In adults of this species, the buccal tube feet are much larger and more robust than the other tube feet. In this little guy the tube feet are noticeably red, but I can't yet tell if they're bigger than the others.

And just for kicks I took another video:

Yesterday I transferred seven urchins onto a glass slide that I've had basking in the sun in an outdoor tank to develop a thin film of algae. As the urchins' mouths become functional they should be able to start munching on the scuzz on the slide. So far they seem happy to be crawling around on the slide but this morning I didn't see any signs that they'd actually eaten anything.

Juvenile sea urchins (Strongylocentrotus purpuratus), age 67 days. 28 March 2015 © Allison J. Gong
Juvenile sea urchins (Strongylocentrotus purpuratus), age 67 days. 28 March 2015.
© Allison J. Gong

The waiting continues....

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