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Thursday, January 31, 2013

Introducing the introvert

Here's an extreme close-up.  Do you have any guesses about what type of organism this is?


This is hard, but it's one of the animals that was in the holdfast post a few nights ago.  Here's another hint:


This is a sipunculan, commonly known as a peanut worm.  These pictures show the most frequently encountered species of peanut worm on Bodega Head, Phascolosoma agassizii.  Alhough often hidden, they're common in intertidal mussel beds and can also be found in rock crevices, kelp holdfasts, and among surfgrass roots.

Externally, you can see two main body parts: the trunk, which is the main portion of the body containing most of the organs; and the introvert, which is long and narrow.  The introvert is extensible — it can be much longer than the trunk when fully extended. 


Note that the skin is papillated (bumpy).  And there are rounded spots on the trunk and dark linear pigment bands on the introvert.


 
Once the introvert starts to extend, it happens pretty quickly (it's fast enough that it's hard to photograph under a microscope!).




Amazingly, the introvert can be fully retracted into the trunk.  Because this was a very small individual and somewhat transparent, you can actually see the introvert inside of the trunk in the image below.  Look for the dark pigment bands visible under the skin.


Although not illustrated in the pictures above, the very tip of the introvert has a tentacular crown (ring of tentacles) used in feeding and gas exchange.  The next photo shows a peanut worm using its tentacles to gather food (detritus) in a tidepool.


I often see peanut worms in crevices.  In his book, Invertebrates, Eugene Kozloff says, "They like tight situations into which their bodies fit almost perfectly."

Below is a view of peanut worms in a shallow, water-filled crevice (only their introverts are visible).  How many peanut worms can you find?

  
There are three peanut worms in the photo above — two larger individuals and one very small juvenile.  The inset below shows you where the little one is.  (When the introvert is retracted, the average length of local peanut worms is ~2-3 cm.)


I don't know if anyone has ever tried, but it seems like the banding patterns on the introverts could be used to identify individual peanut worms (like fluke patterns in Humpback Whales!).

Wednesday, January 30, 2013

Zip line

We interrupt this week's focus on marine invertebrates for a short jumping spider story.  Today I ate lunch on a wooden bench in the warm midday sun.  I looked down to see a dark jumping spider nearby.  I was excited because I hadn't seen one in a while.


The spider was exploring various part of the bench.  Here's a view from above showing the orange sides of the abdomen.


Eventually it spent some time at the lower right corner of the bench.


It turned upside down and started releasing a silk thread!


Spiders often do this hoping to snag the loose end of the thread on a nearby object.  I thought about what might be to the right of the bench. "Hmmm...there's nothing to the right of this bench...except my leg." 

(I was sitting on the ground with my right leg up while trying to photograph the spider.)

The spider turned around and tested the thread to see if it had been anchored.  I was looking through the camera the entire time, so I couldn't really see where the silk had landed.


Then the spider jumped on to the thread (using it like a zip line).


And this is the next picture I got:


The silk had found my leg!  And now I had a jumping spider on my jeans!


What a beautiful little spider.  I was happy to be a part of its afternoon adventures.


ADDENDUM (31 JANUARY 2013): Thanks to Dick Walton for helping to identify this as a Red-backed Jumping Spider (Phidippus johnsoni).

Tuesday, January 29, 2013

The blue-eyed contortionist

Following last night's post, here are a few more images of the crab megalopae discovered in the kelp holdfast at Salmon Creek Beach on 27 January 2013.  All of these photographs were taken under a microscope.  The crabs were very small, only ~4-5 mm long — although this is actually quite sizable for a crab at this stage! 

Here's a reminder of what the crab looks like when its legs are outspread.  Also note the prominent spine pointing backwards at the tail end.  Because of this spine and the size of the crab, Seth suggested this is most likely a crab in the genus Cancer.


I was struck by those beautiful blue eyes.


At this stage, sometimes the crabs crawl on the bottom.  Other times they pull in their legs and swim.  The next image is a view from below while in the tucked position.  You can see the narrow abdomen extending out behind the crab, with feathery pleopods extended.  They flap the pleopods to swim.


In this position, you can also see the claws that are already well developed.



Here's the megalopa in a tucked position again, but this time from above.


When I was reviewing these pictures, I noticed a long, slender, pointed structure lying on the inside of the eyes that I was curious about.  See next image for a close-up.


I haven't watched live megalopae enough to know what these structures were at first.  But after puzzling over them and looking at various pictures, I think they're the hind legs!

I looked for a picture that would confirm my hypothesis and found this one.  This is a view from below.  The crab should have four walking legs.  The yellowest structures visible below are the first two walking legs folded underneath the crab.  But the last two walking legs do appear to be folded above the crab, up and over its back.  I had no idea they would hold their legs in that position.  Two above and two below!


Crabs spend several weeks (a few months in some species) as planktonic larvae swimming in the open ocean.  The larvae then undergo metamorphosis into megalopae and alternate between swimming and crawling on the bottom (or into a kelp holdfast).  They may spend up to a month as a megalopa before becoming a juvenile crab that looks like a miniature adult. 

Monday, January 28, 2013

Home is where your holdfast is

On Sunday, Eric wanted to go for a walk on the beach.  I was a little hesitant, as it was very windy in the late afternoon.  But we decided on Salmon Creek Beach, and in the end it was more than worth it!

The wind and waves had pushed large tangles of Bull Kelp (Nereocystis luetkeana) into the surfzone.  


We wanted to take a closer look at the kelp, but the waves were very strong.  Eric struggled to pull some kelp to shore by holding on to the holdfasts (the rootlike mounds that anchor the kelp to the substrate).


He finally succeeded, and we found a few large holdfasts to look at.  Here's a closer view of the top and bottom.  Note the complex three-dimensional structure and all of the nooks and crannies. 


Many small animals call holdfasts their home.  We started to search carefully and were rewarded for our efforts.

First Eric spotted this small chiton (Mopalia sp.).  (Photographed later under a microscope.)


Then he discovered quite a few crab megalopae.  These are very tiny crabs that are transitioning from a swimming, planktonic stage to a crawling, benthic stage.


Next he found one of my favorites, a beautiful little peanut worm (Phascolosoma agassizii).


And then we couldn't believe our eyes.  Something was reaching out between the branches of the holdfast.  We both leaned in and exclaimed, "Octopus!"


This is one of the smallest octopus we've seen. It's not much bigger than Eric's thumbnail!

It was very active and started to crawl across his hand.


Here's another image to emphasize just how small this little cephalopod is!

[If you focus on Eric's ring, you can see reflections of both of us — I'm at the bottom standing up to take the photo, and Eric is on the upper right (turn your head sideways) looking down at the octopus.]



I'll post some more pictures of these wonderful little animals and talk more about them in the days ahead.

Sunday, January 27, 2013

Grooves on the soles of her shoes

Whew, this species is tough to photograph!  I've been wavering about whether to post these images, but it's what I have ready from today's natural history adventures (watch for some fun marine invertebrate posts coming later this week!).

Can you find the bird in the picture below?


Here's a close-up:


Golden-crowned Kinglets (Regulus satrapa) are tiny songbirds (only 8-11 cm long) that are always on the move.  They tend to prefer conifers (these photos are in Monterey Cypress) and often forage high in the trees, moving quickly among the branches.

They're named for the gold-colored patch on top of their heads.  (Males have orange in addition to yellow.)  In the photos below, you can see the gold crown bordered by black.  Note also the gray nape (hind neck), olive green back, and white underparts.



The facial markings are distinctive and help distinguish Golden-crowned Kinglets from Ruby-crowned Kinglets.  Look for the narrow gray stripe extending downward from the base of the bill, the gray stripe through the eye, and the white eyebrow stripe.



Golden-crowned Kinglets often feed by hanging upside down (see below), gleaning insects, mites, and spiders from the foliage.  

Fun fact: The soles of their feet are grooved — to grip the narrow branches of the conifers among which they prefer to forage.


Golden-crowned Kinglets are uncommon winter residents on Bodega Head.  Recently I've encountered them in the Bodega Dunes Campground in mixed species flocks.  Today they were with Bushtits, Chestnut-backed Chickadees, and a Hutton's Vireo.

Saturday, January 26, 2013

Footprints in the sand

This morning I decided to take a short walk to Salmon Creek to study gulls.  As I started down the beach, I was surprised when this bird flew in and landed on the sand in front of me.


These images illustrate how well the colors of an adult Peregrine Falcon match the tones of winter beaches. 



When the falcon flew off, I was curious about where it had been perched.  Could I see or recognize its footprints? 

I walked up to the site and was intrigued that the bird had been perched on a piece of wood partially buried in the sand. 


You could see where the falcon's feet had made impressions in the sand.  But I'm not sure I could identify these prints in the future.

 

Friday, January 25, 2013

Raven black


Common Ravens (Corvus corvax) 
feeding on a sea lion washed ashore on Salmon Creek Beach
25 January 2013

Thursday, January 24, 2013

Sky-Dancer

I'll never forget one of my early experiences with a bird similar to this.  It was a long time ago and I had been birding for a little while.  I was with a group and someone noticed an extremely pale raptor perched on a post in the distance.  We could only see its face, but I was familiar with most of the local raptors, so I was surprised that it was puzzling and difficult to identify at first.


I was having a hard time with the identification because males of this species are less common than females.  And the males become paler gray with age.  The bird we were looking at was so pale it was almost white.  (A nickname for a very pale male Northern Harrier is the "Gray Ghost.")

The male harrier in these photographs was perched in the salt marsh near Doran Beach.  It appeared to be actively looking and perhaps listening for prey in the vegetation.  (It was breezy at the time, so some of its feathers were being lifted by the wind.)



Earlier in the month I photographed a male harrier in flight at the beginning of the road along Doran Beach.


Male harriers perform a Sky-Dance Display for females.  In spring, watch for these impressive courtship flights with steep, U-shaped undulations (description from The Birds of North America account by Smith et al. 2011).