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Monday, February 24, 2014

Mystery cucumber

On 14 December 2013, I posted pictures of an interesting sea cucumber that I identified as a Stiff-footed Sea Cucumber (Eupentacta quinquesemita).  But now I think that identification was wrong.

Recently, in a Bull Kelp holdfast, we found two more sea cucumbers that looked similar.  This time one of them was extending its feeding tentacles, so I placed it under a microscope to document the tentacles (the first one kept its tentacles hidden).

Here's a view of this cucumber and its exquisite tentacles:

Of course, the dendritic form of the tentacles and the silvery ossicles are beautiful.  But did you happen to notice the dark brown pigment spots?  When I saw those, I became concerned about my original identification because I hadn't seen that coloration described for Eupentacta.

So I embarked on a journey to find out if this could be a different species of sea cucumber.  I couldn't really find a species description that matched this color pattern.  So we decided to look at the shape of the ossicles which is useful for sea cucumber identifications.

The ossicles are the tiny calcified plates visible in the tubefeet, body wall, and tentacles.  They're what make this sea cucumber look so sparkly.

Here's what we found when we looked at the ossicles under a high power microscope.  This is a selection showing a variety of shapes from a tubefoot.

And we had one ossicle photograph from December, too:

Well, these ossicles aren't a match for Eupentacta.  And the closest match we can find is for a sea cucumber called Pentamera trachyplaca.  For comparison, here's an illustration of the ossicles of Pentamera trachyplaca:

Modified from  
Sea Cucumbers of British Columbia, Southeast Alaska and Puget Sound by Philip Lambert (1997).  
Scale bar = 0.1 mm

Interestingly, Pentamera trachyplaca has only been recorded from a few locations: British Columbia, Monterey, and Santa Cruz Island.  So we'll need to confirm that this is the species we've found.  If so, it may be an unusual record for northern California.  We'll report back! 

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