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Showing posts with label fission. Show all posts
Showing posts with label fission. Show all posts

Tuesday, February 25, 2020

The polyp that packs a wallop

Okay, here's the follow-up to last night's post, "The little one with the long tentacles."  

Below is another photo showing a different individual, but the same type of animal:



And here are two close-ups showing the stinging tentacles, and a view of the mouth area in the middle of the ring of tentacles:




The stinging tentacles are a clue that this is a cnidarian (i.e., the group that contains jellyfish, sea anemones, corals, etc.).  But which one is it?

Because this stage of the life cycle is so small (only a few millimeters long), many people haven't seen it before.

These are jellyfish polyps (also known as scyphistomae)!  Eric found them growing on sea squirts at the Spud Point Marina docks.  

Referring to the diagram below, the basic life cycle goes like this: free-swimming adult medusae release gametes (eggs or sperm); a fertilized egg develops into a planula larva; the planula eventually settles and undergoes metamorphosis into a benthic (bottom-dwelling) polyp; the polyp eventually undergoes fissioni.e., it buds off tiny juvenile medusae (called ephyrae) that eventually grow into the adults to complete the life cycle.

Modified from:  Living Invertebrates by Vicki Pearse, John Pearse, Mildred Buchsbaum, and Ralph Buchsbaum.  1987.  Blackwell Sci. Pub. and Boxwood Press.


In the image below, the polyp might be in the early stages of strobilation (note the banding pattern in the polyp):



And here's one more showing the beautiful but deadly tentacles (at least to tiny, microscopic prey):


P.S.  I'm not sure which species of jellyfish this is, but perhaps someone will recognize it and let us know.

Thursday, January 30, 2020

Dividing


During field surveys last week, I noticed this very elongated sea anemone.  It took a few seconds for me to register that this Moonglow Anemone (Anthopleura artemisia) might be dividing, and I wasn't sure that I'd seen this species dividing before.  (It's known that Moonglow Sea Anemones can undergo fission, but I'm not sure I've seen it myself.)  So I thought it would be worth posting a photo for the record.

In the Bodega Bay area, the anemone best known for undergoing longitudinal fission (basically dividing into two) is the Aggregating Sea Anemone (Anthopleura elegantissima).  One individual begins to stretch out, then eventually divides in half, regenerates a few internal structures, and becomes two genetically identical individuals (clones).  The process is illustrated below.  The right column shows the external view of a dividing anemone, and the left column shows the internal view:


Modified from Sebens, K.  1983.  Morphological variability during longitudinal fission of the intertidal sea anemone, Anthopleura elegantissima (Brandt).  Pacific Science 47: 121-132.


In case you're curious to see what this looks like (and if you want to watch for it yourself), here are older photos of Aggregating Sea Anemones in the process of dividing:



 
(Don't worry about the yellowish color of the anemone above; they're pale when they're growing in very shaded environments.)

Maybe next time we go back to the field site where the first photo was taken we'll see two Moonglow Sea Anemones in the little pool!  Stay tuned...