Nostalgia for stars

  

Sunflower Star (Pycnopodia helianthoides).  Sometimes I really miss seeing Sunflower Stars, so here's an older photo from 2006.  (We haven't seen this species in the Bodega Bay area since 2014 after their populations were decimated by disease.)

 

Where have all the sunflowers gone?

 

This picture of a juvenile Sunflower Star (Pycnopodia helianthoides) was taken on 12 July 2014.  I haven't seen a Sunflower Star in the intertidal zone since then.  It appears that this species has declined dramatically in the Bodega Bay area, likely due to the effects of wasting disease. 

This juvenile was ~70 mm across, and had ~14 arms.  Here's a picture for scale:

 

I showed a series of smaller Sunflower Stars from December 2013 through May 2014.  If you'd like to review, links to previous pictures are below:

• 14 mm, 8 arms, 17 December 2013

• 20 mm, 10 arms, 31 December 2013

• 40 mm, 12 arms, 17 May 2014

Here's hoping that some of these juvenile Sunflower Stars have survived:

 

And that someday soon we'll be seeing adults again — like this one from 12 May 2012.

 

Adding on

In December 2013, I posted about an 8-armed Sunflower Star (Pycnopodia helianthoides) and a 10-armed individual.  To review those images, see the posts from 17 December 2013 and 31 December 2013, respectively.  

I mentioned that Sunflower Stars add two arms at a time, and may end up with a total of 20 or more arms.  So you might be able to guess what's coming next!

 

It depends a little bit on exactly how you count, but this juvenile Sunflower Star has at least 12 active arms.  It also has two developing arm buds, so some people may count 14 arms.  The entire sea star, from arm tip to arm tip, was approximately 4 cm (1.5 inches) across.  It was photographed on 17 May 2014.

Remember that Sunflower Stars add two arms at a time and they add them bilaterally, or one on either side.  In the picture above, arms 11 and 12 are distinctive because they're shorter than all of the other arms, but they still have active tubefeet.  In the image above, they're at the top and bottom of the sea star.

Arms (or arm buds) 13 and 14 are very small.  They are adjacent to arms 11 and 12.  They have very pale tips.  

Below are two extreme close-ups that I hope will help you see all three arm types — the regular-sized arms; arm 11, which is a little shorter than those; and arm 13, which is a tiny bud just to the right of arm 11.  [If you're wondering about the white circular disc on top of the sea star — it's the madreporite (or sieve plate) that drives the sea star's water vascular system.]

 

 

It's been a lot of fun to see these Sunflower Stars growing up over the last 6 months — from about 14 mm with 8 arms in mid-December to 40 mm with 12 (or 14?) arms in mid-May.

Here's one more picture of this recent individual exploring a local tidepool:

 

See-through

In mid-March, I was trying to photograph a small Sunflower Star (Pycnopodia helianthoides) that we had discovered rafting in a Bull Kelp holdfast.  Eric came along and looked through the microscope.  By the way he was taking a little extra time, I knew he was noticing something interesting.

He turned and said, "Those dark areas are the pyloric caeca!"

We had observed the way these small Sunflower Stars looked dark in the center (see below), but without looking closer, we had assumed it was pigment.  Now with a better view under the microscope, we could see that it wasn't pigment.  The body wall of the sea star was transparent, so we were seeing through to the inside of the sea star and actually viewing the digestive system!

 

Here's a diagram with an explanation (below).  A sea star has two stomachs — the cardiac stomach is the one you might be more familiar with; it's everted (extended outside of the animal) when the sea star is feeding.  The pyloric stomach is located above the cardiac stomach, and it has branches that reach into the arms.  These branches are called pyloric caeca (there are two in each arm).

 

Modified from Biology of the Invertebrates (Pechenik 2010) 

Many sea stars store energy in their pyloric caeca during the spring and summer.  In the fall and winter they transfer that energy to their gonads for reproduction.

When sea stars are older, their body wall is no longer transparent, so the pyloric caeca can't be seen.  It was a treat to be able to see both the polygon-shaped pyloric stomach and the pyloric caeca in this juvenile Sunflower Star!

(Note that the newest arms, the shortest ones, don't yet have pyloric caeca, but they will develop them later.)