Emily and Kate found this amazing larva in a plankton tow off Bodega Head on 9 July 2015.
All of these pictures (and video) were taken through a microscope:
This is the planktonic larva of a marine worm (Family Oweniidae). It's an unusual larva, and it has an unusual name — it's called a mitraria.
The following is a simple illustration to help visualize the major parts. There is a cap-like portion called the episphere (note that a ciliated band runs along its perimeter — and in the species shown here, four segments of the band have orange pigment). The cluster of long setae (bristles) really stands out.
Modified from Smith, D.L. and K.B. Johnson, 1996. A guide to marine coastal plankton and marine invertebrate larvae, 2nd ed. Kendall Hunt Publishing, Dubuque, Iowa.
We think there's something about the structure of the setae that causes light to be reflected in various colors (mostly blue and green, with occasional orange).
When a mitraria larve is disturbed, or threatened (e.g., by a predator), it spreads its setae wide in a radiating pattern, perhaps as a defensive strategy (to make it less palatable).
Although the pictures give you some idea about the wonderful color patterns created by the setae, there's nothing like seeing this "light show" in video form.
Watch, and wonder!
(Click on the title of the video to see a high resolution version — highly recommended!)
Thanks to Emily and Kate for sharing this wonderful larva with us...and with you!