What is it?

we came upon this odd looking, uh, thing, walking along the beach. and noticed that the beach was positively rife with them. looks like an aquatic plant. feels like one. mostly seaweeds don't grow out of sand. perhaps it is rooted to a hidden rock? to see what happens when one steps near this click here. wow! did you see that? ok, it's some sort of critter, maybe a clam. but i can't find any reference to a clam with a fringed siphon. does this clam have some sort of symbiosis with a plant? we walk at low tide quite often, and i always watch out for indications of clams. in my rather limited exploration of local beaches i had not seen an adorned clam siphon. so, using an empty clamshell, i explored neath the surface. i'm fairly certain that no organism was harmed by my digging, because i did get a glimpse of what appeared to be a horse clam siphon. i don't think that i was chasing a geoduck because a geoduck (pronounced gooeyduck) has a double siphon, with two holes. the siphon i caught a glimpse of had one hole, just like horseclam siphons i have seen on other beaches.

i was loathe to make a full out assault here, as my clamdigger license expired march 31. and i don't like horse clams anyway. just wanted to see what is down there. any other opinions about this?

update: sorry some of you can't see the incredible interesting and artistically shot nature movies. they work on our pc running xp pro. i have changed the movie format slightly (from "web streaming" to "web" as the output of imovie). i would love to hear from anyone if you can see the movies now.
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another update: i'm sticking with my horse clam guess because i found a reference which mentioned that they sometimes have barnacles or algae (!) stuck to their siphons. i guess the scientific method requires that i go back there and dig one up. i renewed my license today and went to my favorite super-dooper secret clam place and will have a nice side of steamers with dinner.

we created the movies on our digital camera, which makes movies in .mov format. my mac opens them in quicktime. the 30 second clip of me digging is 14 MB. i put it in imovie, which compresses movies for web use. the output is 736 KB. i have uploaded both formats to our disc storage, and both play when invoked by a link but the uncompressed format straight from the camera takes a looong time to load.

thank you all for tuning in.