Goodbye, Rubra Tuesday

A couple of months ago, Eric noticed this interesting sea cucumber in the rocky intertidal zone.  Its coloration caught his eye.  We've encountered quite a few small white sea cucumbers in this area, but this one had orange at both ends.  (Note, the cucumber was ~16 mm long.  The dark areas are bits of woody debris.)

 

Eric has been trying to document the local sea cucumbers.  Over the years, we've realized there are several species of little white cucumbers that can appear very similar to each other.  So far we've found Eupentacta quinquesemita, Pentamera pediparva, and Pseudocnus lubricus.  When we looked closely, this individual didn't look quite right for any of the aforementioned species.  

Here are a few close-ups taken under a microscope.  Note that the tubefeet are scattered across the body — i.e., they aren't arranged in regular rows.

 

 

Also, this sea cucumber's ossicles (tiny calcified plates embedded in the skin) are dense!

 

We couldn't find this sea cucumber in Phil Lambert's Sea Cucumbers of British Columbia, Southeast Alaska, and Puget Sound (1997).  We also had trouble locating it in the Light and Smith Manual (2007).  We kept trying to identify it via the key.  Most of the characters seemed right for Pachythyone rubra, but the key said this species was red or reddish- orange.  So we decided to look at the ossicles.

Here are a few pictures of the ossicles that Eric photographed under a high-powered microscope:

 

The Light and Smith Manual didn't include an illustration of Pachythyone rubra's ossicles.  But we found a diagram in another publication and it was a perfect match!

 

Ossicles from body wall, including (A) 4-holed buttons; (B) reticulated plates; and (C) supporting tables from tube feet.  Modified from Bergen. M.  1996.  Class Holothuroidea.  In J.A. Blake, P.H. Scott, and A. Lissner (eds). Taxonomic Atlas of the Benthic Fauna of the Santa Maria Basin and the Western Santa Barbara Channel (Vol. 14, Miscellaneous Taxa, pp. 195-250).  Santa Barbara: Santa Barbara Museum of Natural History.

The ossicles confirm that this species is Pachythyone rubra.  Although the Light and Smith Manual described the adults as red/reddish-orange, perhaps the coloration can vary, especially in juveniles and small individuals?  

This more southern species of sea cucumber primarily occurs from Monterey and south.  It has been found one other time in Bodega Bay (in 1976).  As far as we can tell, Bodega Bay is the northern range limit for Pachythyone rubra.  If you find one north of Bodega Bay, we'd love to hear about it!

P.S.  An interesting side note: Pachythyone rubra is a brooder.  Females brood the embryos within the body cavity and release juveniles when they're ~1-5 mm long.

P.P.S.  If felt good to finally hang a name on this cucumber!