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Sunday, August 10, 2014

Clinging to an eelgrass blade near you

Katie had been seeing these small hydromedusae among the eelgrass (Zostera marina) in Bodega Harbor.  We finally looked at some under the microscope together and believe we identified them as Cladonema californicum

There are some amazing things about this species and it has some fun connections to wonderful people and local places, too.

Cladonema californicum was first described by Libbie Hyman in 1947.  To describe the species, she used organisms sent to her that were collected in Tomales Bay (near Dillon Beach) by Frank Pitelka in 1941.

Here are two figures modified from Hyman's paper.  The first shows the most obvious features (that you can identify in the next photo!) and the second highlights the unusual branched tentacles one branch that ends in a sucker and the other with stinging branches.   


Both figures modified from Hyman, L. H.  1947.  Two new hydromedusae from the California Coast.  Trans. Am. Microsc. Soc.  66: 262-268.

Now here's a close-up photo of the living hydromedusae.  Look for all of the parts mentioned above.

Can you see how the hydromedusa is using the tentacle branches with suckers to cling to the eelgrass blade?  Many of you are probably used to seeing hydromedusae swimming through the water column (like jellyfish).  This species is unusual in that it has adopted a partially benthic lifestyle.  It holds onto the substrate with adhesive pads and then spreads its stinging tentacles to capture prey (e.g., small crustaceans such as copepods).

The next image highlights the fascinating suckers.  The hydromedusa was crawling to the other side of the eelgrass blade when I took this picture.

While watching the hydromedusa, we also observed an interesting behavior.  Occasionally it would draw its stinging tentacles and sucker tentacles into the bell and drag them past the oral tentacles (see next photo). This looked like feeding behavior (like wiping your fingers across your lips), although I'll admit that we didn't actually see the hydromedusa catch any prey and I'd feel more comfortable with more observations to say for sure.

P.S.  Libbie Hyman was one of the most influential invertebrate zoologists in North America.  She single-handedly wrote a six-volume treatise called The Invertebrates between 1940 and 1967.  The format of these books was later adopted by other invertebrate textbooks in use today, and her volumes are still consulted and admired for their depth and comprehensiveness.

Here's a nice photo of Libbie Hyman from the American Museum of Natural History's publication about her:

From Libbie Henrietta Hyman: life and contributions.  American Museum Novitates no. 3277 (published in 1999, edited by Judith Winston).

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