Doing my homework

Last Wednesday, I wrote about some of the animals we found on Crescent Beach at low tide. In that post, I identified two clams as geoducks, but I later had to retract that. (I amended the post.)

The clams, at least one of them, were gapers, aka horse clams, or horseneck clams. Here's how I know:

• First, gaper clams and geoducks have a one-way digestive tube. It has two openings, an intake siphon and an excurrent siphon, both of which travel through the neck. In geoducks, these siphons share an exit "mouth", which can look almost like paired nostrils. In gapers, the two separate; each siphon has its unique, round opening. In all our photos, but one, the "mouths" were of the gaper type.

• Second: a gaper clam has tentacles at the mouth of one of its siphons. Geoducks do not. Our clams did.
  

Click on this to see the golden tentacles at the mouth. Probably Fat Gaper, Tresus capax.

• Third: see that white blur between the tentacles? Here it is again, a bit clearer:
  
  
  
  Gaper Pea Crab, Pinnixa litoralis.
  
  
  It's a tiny white crab. These crabs live inside the mantle of the Fat Gaper. I see no mention of them with Geoducks.
  
  Here's another:
  
  
  
  Female Pea Crab, in Gaper Clam siphon.
  
  
  So I was wrong about the species of a big clam, and here I am giving the sex of a tiny white crab, based on a few blurry photos. That's because these crabs are easy; the female has a space between the pincer tips when they are closed. The male doesn't.
  
  Each clam, when the pea crabs are present, has two, a small male and a larger female. There may be others, but they will all be sexually immature.
  
  The crabs don't seem to harm the clam. They eat food scraps in the cavity.
  
  And here's a clear photo of pea crabs in gaper clams from Washington State University.

More info on these clams:

1. Horse clam. From Wikipedia.

   The horse clam (Tresus nuttallii and T. capax) are related to the Geoduck, though smaller, with shells up to eight inches long (20 cm), weight to 3–4 lb (1.4–1.8 kg). Two similar species of horse clams inhabit the Pacific coast intertidal zones: the pacific gaper, Tresus nuttallii, more abundant south to California; and the fat gaper, T. capax, more abundant north to Alaska.

2. Entertaining instructions for digging out geoducks, with photos, from Washington Department of Fish and Wildlife. (Aren't fish "wildlife"?)

   The clam's name, pronounced "gooey-duck" is of Native American origin and means "dig deep." It is variously spelled goeduck, goiduck, or gweduck.
   

   Also includes photos of siphons, exposed and retracted.
   
   
3. Flickr photo of geoduck siphon.
   
   
4. Photos of horse (gaper) clam siphons, underwater, and with pea crab. From Oregon Dept. of Fish and Wildlife.

By the way, remember those worm tubes sticking out of the sand? Here's one. It's about an inch tall.


And here's another, with the clam siphon and crab pincers for size comparison.

Worm tube and clam siphon

This tube has the worm's tail end sticking out. I'd never seen that before. It's a Bamboo worm, the same as the one we found on Crescent Beach last week.

A few feet away, something else left a tube:

Not a worm tube.

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Watching where we step

On a mile-wide, featureless, sandy beach, what is there to see, besides sand and sky? Plenty. But it's mostly in hiding. I've been having fun blowing up our photos of Sunday's walk to full size, to see what we missed.

Sea lettuce and a mudflat snail, Batillaria attramentaria. No telling what's underneath.


Brown seaweed, probably a dulse. Eelgrass and roots.

So far, so good. Eelgrass and seaweed are easy to see. But look again! See those little yellowish dots on the eelgrass? They're egg cases, possibly of the Black Dog Whelk, Illyanasa obsoleta*.

Here are some more, doing their best to blend in with the bubbles.

Brown tuft, navel-lint algae. With eelgrass and snail eggs.

The snails are even better at hiding; they burrow right under the wet sand. I dug a few out; mostly Black Turbans, and a whelk or two. One on the upper left, below, looks like a mudflat snail, going by the shape.


In a photo of seaweeds and eelgrass, I found this tiny collection:

White tube discarded by a worm. And what looks like whelk eggs. (Nucella sp.)

If I had seen this at the time, I would have taken a close-up. But they were so small, I missed them even on the first two examinations of the photo.

This tangle of weeds and -- something -- is intriguing:

What is that red, segmented, tentacled thing? Worm or weed?


A close-up of the end, with "tentacles". Some kind of spaghetti worm? **

This is a worm, at least. We found it writhing in an inch of water. It's about 6 inches long.

Red-banded Bamboo worm, Axiothella rubrocincta. The red rings are bristled. (Barely visible.)


Clear view of the tail end. The head is already back under the sand, and digging fast.

Their tubes were scattered here and there around this area of the beach, mostly poking just an inch or so above ground. The worms stay in these tubes; I wonder why this one was on the surface.

On the opposite side of the bay, at Boundary Bay Beach (and this is all Boundary Bay, but this side is Crescent Beach), the sand is dotted with the fecal castings of lugworms. On the Crescent Beach side, the coils of worm poop are less frequent, smaller, and finer. Look for them around these geoducks:

Pacific geoduck, Panopea abrupta. Up to 9 inches across the shell, and 20 lbs. Lifespan: 168 years!

When I touched this geoduck (pronounced gooey duck) with a toe, it retracted itself back under the sand, squirting at me as it went.

A horse clam, covered with algae and seaweed, and accompanied by grey mounds of worm poop.

(Update: I had identified this as a geoduck. I was wrong. Looking more closely at the siphon mouth, I realized that the edge of the mantle is tentacled; this identifies it as the gaper, or horse clam, Tresus nutalli. (The tentacles are green, which distinguish it from T. capax, where they are gold. I still think, though I could be wrong, that the first one is a geoduck. Neither it, nor one other similar one that we photographed show any sign of tentacles, and the other one has the characteristic one siphon, two openings of the geoduck.)

Look in front of the clam siphon; that brown coil is not lugworm poop; it looks more like a ribbon worm of some kind.

Mouth of the gaper clam.

One last critter. There were quite a few of these. But we never saw them unless we were about to step on them; then they shot out of the sand, sped a few feet away, and -- disappeared, even though we were looking right at them. One moment they were swimming, the next, there was not a trace of them.

Can you see the tidepool sculpin here? I have increased the contrast to make him stand out.

Tidepool sculpin, Oligocottus maculosus. Supremely camouflaged.

So many new things! So much to learn! What fun!

* Photo in Marine Life of the Pacific Northwest, MC198, p.228. Also, see my last year's post, No boots, no bags, some goodies anyhow, for macro photos.

** It's really an eelgrass root, with its rootlet "tentacles".

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