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Monday, November 12, 2012

Twinkle, twinkle, little stauro

Today, Eric's sharp eyes found one of the most intriguing intertidal inhabitants of Bodega Head.  This is a little-known marine animal called a stauromedusa.  They're cnidarians, related to jellyfish, sea anemones, and hydroids.  Most of them are very small (a few centimeters tall) and cryptic (blending in with algae or seagrass), so they aren't encountered often.  [The one in these photographs is ~1 cm tall and is attached to coralline algae.  It was found in a wave-exposed surge channel.]

Several features stand out.  Note the long, flexible, contractile stalk.  Stauromedusae often stay in place, but they can also let go and move around.  Here are two views of the stalk when extended and pulled in (below). 

Opposite the disc is a large bell-shaped calyx.  To make it easier, review this illustration and then search for the features in the images.

Illustration modified from the following:  Larson and Fautin, 1989.  Stauromedusae of the genus Manania (= Thaumatoscyphus) (Cnidaria, Scyphozoa) in the northeast Pacific, including descriptions of new species Manania gwilliami and Manania handi.  Canadian Journal of Zoology 67: 1543-1549.

The calyx has eight clusters of short tentacles surrounding the mouth.  The tentacles contain cells with nematocysts (tiny harpoons) for capturing prey such as copepods and amphipods.

In between the tentacle clusters are small anchors.  The anchors are useful for reattaching (if the disc becomes detached) and may aid in securing food.

The white and brown zigzag markings running between the stalk and the tentacles are reproductive structures or gonads.

We believe this is Manania gwilliami.  It was first described in 1989 and named after G.F. Gwilliam — an early graduate student of Cadet Hand (the first director of the Bodega Marine Laboratory) and one of the first people to study stauromedusae in the eastern Pacific.

Manania gwilliami occurs along the Pacific Coast from British Columbia to Baja California (records from Oregon and Washington are apparently lacking, but it's likely that the species is found there).  It prefers surf-swept rocky outer coasts.

When I first learned about stauromedusae they were thought to be most closely related to jellyfish (visualize a tiny, upside-down jellyfish on a stalk).  But recent molecular studies have suggested that they belong in their own class, Staurozoa (Collins and Daly 2005).

We've been wanting to find a local stauromedusa for a long time.  What luck to find our first one on Bodega Head on a beautiful November afternoon!

You can learn more about stauromedusae at the Encyclopedia of Life web pages.

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