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Sunday, February 19, 2012

A two gooseberry day

Early in the afternoon on 18 February 2012, I photographed this Red-flowering Currant (Ribes sanguineum var. glutinosum) in the Bodega Dunes campground.  This shrub is uncommon on the Bodega Head peninsula, but it's one of the first to start flowering.  Currants are in the Gooseberry Family.


Later the same afternoon we encountered quite a few sea gooseberries (Pleurobrachia bachei) washed up on the beach.  On the sand they look like small transparent marbles or crystal-clear gelatinous spheres.


As I was thinking about these two sightings, I realized I hadn't ever heard why sea gooseberries are called gooseberries.  Doing a quick Internet search I encountered a few diagrams of gooseberry fruit (see below).  There is an amazing resemblance between these fruits and the planktonic marine invertebrate! 


To make this visual comparison easier, I photographed a few sea gooseberries in a small aquarium and under a microscope.

Sea gooseberries are ctenophores (commonly known as comb jellies).  Ctenophores are named for their eight rows of ctenes, or comb plates (fused bands of cilia).  The combs beat in metachronal waves to propel the ctenophore.


Sea gooseberries are predators that troll for zooplankton prey with two long tentacles (the genus, Pleurobrachia, means "side arms").  The tentacles contain cells that produce a sticky adhesive which traps the prey, e.g., copepods.  (Unlike jellyfish, ctenophores do not have stinging cells.)


To transfer the prey to the mouth which is opposite the tentacles (see below for circular feature in center of ctenophore), the ctenophore does a somersault and wipes the tentacles along the mouth.


Here are a few more photos — a sea gooseberry swimming, a view from below, and a close up of the tentacles.  Notice that the side tentacles (tentilla) can also be extended.



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