Spiderlings?

  

While doing some surveys during the low tide this afternoon (22 November 2022), Eric kept spotting these very small sea spiders (pycnogonids).  This species, Pycnogonum stearnsi, is common in this area, but we don't often see juveniles.  The ruler above shows millimeter markings, so this sea spider was only ~3 mm long.  (The sea spider is crawling across a purple sponge.)

Here's another photo  — with one individual of a more typical size (~8-10 mm long) and another small juvenile to the right:

 

 

Fantastically spinose

 

Recently, Maddy found several of these sea spiders (pycnogonids) living among low intertidal tunicates on Bodega Head.   This species is very distinctive among our local sea spiders because of the many spines covering its body.  Below is a close-up view of the top surface of the sea spider.  Notice the numerous cactus-like spines around the legs and abdomen:

 

As Joel Hedgpeth noted in his 1951 paper on the sea spiders of Dillon Beach, this species is “fantastically spinose” and so it seems appropriate that it is named Nymphopsis spinosissimum!  

The drawing below from Hilton (1942) shows the spiny body plan of this species.  You can also see another important distinguishing feature of this species — the three tubercles (tower-like structures) in a row on the upper surface of the sea spider:

Modified from: Hilton, W.A. (1942) Pycnogonids from the Allan Hancock Expeditions. Reports of the Allan Hancock Pacific Expedition 5 (9): 277–339.

In the side view below, you can see the spiny abdomen in the back (it looks like a finger pointing to the left), then the three spiny tubercles in a row, and lastly the ocular tubercle at the front (the projection on the right side with reddish coloration bearing the shiny eyes). 

Finally, here’s a head-on view of the sea spider, showing its grasping claws (chelicerae) and the ocular tubercle above:

 

It seems possible that all of these sharp spines might help defend the sea spider against being eaten, but very little is known about the biology of this species.    

Many thanks to Maddy for finding these sea spiders and Eric for taking the excellent photographs! 

Leggy

A couple of nights ago I promised to share more information about this sea spider:

 

We're slowly trying to document the diversity of local sea spiders.  Maddy spotted this one in July and we hadn't knowingly observed this species yet, so Eric took some photos for the record.  Meet Ammothea hilgendorfi!  The entire sea spider is ~12 mm across (from leg tip to leg tip).

 

Sea spiders aren't necessarily easy to photograph, but these are terrific shots (thanks to Eric's patience!).

Below is a series of images showing some of the distinguishing features used to identify Ammothea hilgendorfi to species.  First, a diagram so you know what to look for:

Modified from Cole, Leon J. 1904. Pycnogonida of the west coast of North America. Harriman Alaska Expedition, Volume 10: pp. 249-298. 

Look for the eyes (two are visible from the side, a pair of circles on a small raised cone) and the abdomen (also a raised projection, at the end opposite the eyes):

 

Next, here's a view of the proboscis.  Look for the large white tubular structure projecting forward — it's below and extends out in front of the eyes.  The proboscis is used in feeding (suctioning and pumping). Although it's not visible, there's a small, triangular mouth at the far end of the proboscis.  (Sea spiders are parasitic on other animals like hydroids, bryozoans, and sea anemones.)

 

Eric also captured a nice view of one of the claws (at the tip of a leg).  It reminded me of the claw of a sloth — useful for grasping limbs.  In this case the sea spider might hold on to the branches of colonial animals such as hydroids:

 

You can compare the photos of these features to the diagram above to see that they are a good match for this species.

Many thanks to Maddy for spotting this intriguing pycnogonid and to Eric for the photos!

 

Celebrating eight

For 8/8: a beautiful local pycnogonid (sea spider)!

 

I'm running out of time tonight, but we'll share more information about this species soon!

Papa pycno

Here's one for all of the sea spider enthusiasts out there!  

I've shown a few sea spiders (also known as pycnogonids) on this blog, but this is the first post about Tanystylum californicum.  Eric spotted this individual earlier in December.  It's <5 mm across (including the legs).

 

Here's a closer view.  Although this sea spider was small, Eric could tell it looked "spiky" even before looking through a microscope:

 

If you look closely in the photo above, you might notice some white clusters underneath the sea spider.  Flipping the sea spider over revealed that this was a male.  

In the photo below, note the three white clusters of embryos.  In most pycnogonids, there is paternal brood care (unusual for marine invertebrates) — males carry and take care of the developing embryos:

 

Look for the special hook-like appendage, called an oviger, that holds the embryos.  (There are two ovigers, but one is hidden below the embryos.)  

And note that the three different embryo clusters are in different stages of development.  The whitest, opaque cluster (on the left) is the youngest; the cluster with embryos showing tiny red eye spots is further along (on the upper right); and the lowest cluster is the oldest, with larvae hatching!

 

Here's a zoomed in view of a couple of larvae (called protonymphons) crawling on the outside of the embryo cluster:

 

The larvae were tiny, but here's a close-up of one.  Note the fairly substantial claws (chelifores) pointing downward.  Sea spider larvae will undergo many molts before they look like the adults!

 

To see some of the previous posts about sea spiders, check out "One of Joel's old friends'" on 13 January 2014; "Different mates" on 27 February 2014; and "Along came a sea spider" on 15 May 2013.

 

Different mates

In January I mentioned that there is male parental care in sea spiders.  Here are a few pictures to continue that story.

This is Pycnogonum stearnsi, a common local sea spider often associated with sea anemones.  Its legs are pulled in, and it's "hiding" a large mass of fertilized eggs — the white mass barely visible below the sea spider.  Males have specialized legs (ovigers) for carrying the developing embryos.  [For orientation, the anterior or head end (note the brown eyes) is pointing towards the top of the image.]

 

Viewed from below you can see the impressive number of embryos.  And if you look very carefully, you should be able to see something else that's notable.  Not all of the embryos are alike!

 

It may help if I zoom in.  (And remember that you can click on the picture for a larger version.)

 

Can you see that there are two different masses of embryos, in different developmental stages?  The uppermost embryos have reddish spots and are more mature...while the lowermost embryos are pure white, lack those spots, and are younger.

Here's an even closer view of the uppermost embryos (below).  The reddish spots are eyespots.

 

Male sea spiders often gather different egg masses from multiple females.  It's possible that the two egg masses are from the same female, but in a study done where they tested this (extensively), it was much more likely that different egg masses carried by one male were from different mates.  (The egg masses could be from up to 4 different females, but more often they were from 1-3 females.)

The males will carry the embryos for 1-2 months until the larvae hatch.

Facts above from:  Barreto, F.S. and J.C. Avise. 2010. Quantitative measures of sexual selection reveal no evidence for sex-role reversal in a sea spider with prolonged paternal care.  Proc. R. Soc. B 277: 2951-2956.

One of Joel's old friends

I know, you've been wondering when another mystery close-up might appear.  Well, here you go!  (Highly magnified microscope view is below.)

 

I'll pull back a little to let you see more of the animal:

 

Yes, those are eyes near the top of the photo.  There are four eyes (although not all of them are in view) and they're located on an "ocular tubercle."  And yes, those are "claws," formally called chelae, in front of the eyes.

Do you have a guess?

(Warning: The next picture may give the answer away.)

 

This is a sea spider, or pycnogonid, called Achelia chelata.  It was ~5 mm across.  It was fun that Eric found it in Bodega Bay as there's another local connection for this species — Joel Hedgpeth, a long-time Santa Rosa resident, re-described it in 1940!  (See Joel's drawing below, and compare it with the second picture of this post.  Once again, note the prominent chelae, or claws.  They're an important feature for identifying this species of sea spider.)

 

Modified from Hedgpeth, J.W.  1940.  A new pycnogonid from Pescadero, Calif., and distributional notes on other species.  J. Wash. Acad. Sci. 30: 84-87.

This record is also interesting in that it sounds like this species of sea spider is relatively uncommon.

Here's a view of Achelia chelata from above, as well as another comparative drawing from Joel's paper:

 

 

And one more thing that I learned about sea spiders from the encounter with this species.  While trying to identify it, I noticed that one of the leg segments (on each of the legs) was quite swollen and pale (see third photo of post above).

So I zoomed in for a closer view:

 

Can you see the little white dots in the swollen segment?  Can you guess what they are?

Here's an even closer view.  The answer is below the next image.

 

Eggs!  Sea spiders have very small, thin bodies, so a portion of their gonads extends into their legs.  In females, the eggs develop in the legs!  Eventually they will be extruded through a pore (on the legs) and then fertilized and gathered by a male who will then carry the cluster of eggs and brood them until they hatch.  I had known about male parental care in sea spiders, but was not aware that the eggs developed in the female's legs!

What fun to discover another local connection to Joel Hedgpeth, to document a new location for this species, and to learn a fascinating fact about the biology of sea spiders!

Along came a sea spider

In late April, I was looking through a microscope trying to photograph a local hydroid when I was distracted by something orange with long legs:

 

I zoomed in for a closer look:

 

This is a pycnogonid, or sea spider.  It's a little hard to make everything out at first, but I just had to post these pictures because this animal is so unusual.  

This sea spider is mostly transparent.  The orange lines are branches of the gut that extend throughout the body and into each leg.  (Somehow this patterning made the sea spider look like some sort of Halloween skeleton to me!)

The head is on the left side and if you look carefully you can see small silvery spots that are the eyes. [There are four eyes, but all four are not always visible.]  The two arching appendages on either side of the eyes are chelicerae — the presence of chelicerae tells you that sea spiders are related to horseshoe crabs, spiders, and scorpions.

After that, the body (or trunk) is narrow, but there are very long legs extending out to either side.  In the next photo, the sea spider has turned to face away from the camera and is now crawling along a branch of the hydroid.  Note the sharp curved claws at the tips of its legs for holding on (reminiscent of a sloth).

 

Close-up of leg and claw wrapped around hydroid branch:

 

I believe this sea spider had just eaten one of the hydroid polyps — see the pink mass next to the sea spider in the following image.  The sea spider has a long proboscis that it uses to suck fluids out of its prey.

 

There are many other interesting facts to share about sea spiders, but I'll save those for another night. 

For now, since you've become familiar with what this sea spider looks like, can you find it in the photo below?  The transparent-and-orange coloration is effective camouflage against the backdrop of the hydroid, but I think you'll be able to find it if you search carefully.

 

The sea spider is in the lower right corner, at the lower end of the rightmost brown hydroid branch.