What you need, my friend, is Robin D. Gill's "Rise, Ye Sea Slugs!": A Theme from In Praise of Old Haiku, with Many More Poems and Fine Elaboration (Paraverse Press, 2003; ISBN 0974261807). The preface, "holothurian cuture in Japan," is available here:
http://paraverse.org/risesample.htm
I call to your attention the following paragraph, which may or may not elucidate anything:

In Japan, one never knows when or where one is going to run into a sea cucumber (namako). There is, of course, our culinary culture, boasting various namako delicacies; but the namako provides us with far more food for our head than for our belly. Holothurians pop up in science fiction under guises such as the “sea-cucumber starman” (namako-hoseijin), in pop music songs such as the recent “sea cucumber who slept-in” (neboke-namako), in midi files (short animation) where they dance, snore and otherwise show off, in web-page names such as “sea cucumber soliloquy” (namako-no-hitorigoto, an exceptionally boring diary) or “sea cucumber shrine” (namako-jingu, a fortune-teller’s web-page), in the martial arts as the “sea cucumber sword-guard” (namako-tsuba) of Miyamoto Musashi or simply the “sea cucumber” (namako) once used to restrain criminals (ed. note: It is vernacular for the sodegarami, or “sleeve-grabber.”), in the marital arts as the “sea cucumber ring”(namako-wa), a tickler, in architecture as raised grout “sea cucumber walls” (namako-kabe), “sea cucumber roof tiles” (namakogawara),“sea cucumber (corrugated) iron sheet” (namako-ita) and swollen rounded “sea cucumber (door) frames”(namakobuchi), in foundries as “sea cucumber (pig) iron” (namakosen), in dress as bumpy “sea cucumber weave” (namako ori) and stylish sea cucumber tie-dye (namako shibori), in pottery as the complex purplish-gray sea cucumber glaze (namakogusuri) for expensive “sea cucumber hand-warming-pots” (namako-hibachi) or “sea cucumber-handled [pots]” (namakode), in folk events, such as occasional reenactments of ancient tribute-bearing delegations or the annual “sea cucumber drag” (namako-hiki), where a sea cucumber doll is dragged around by children on the day the Big New Year gods are sent off, or even as a mascot for a low entropy-creating ecological lifestyle. (ed. note: To get a gut-feeling of why this book uses the scientifically incorrect “slug,” compare the sound of “sea slug starman,” “the sea slug who slept in,” or “sea slug soliloquy” with the cacophonous “cucumber” versions of the same, above!)

Seconding Mr Hat in recommending "Rise, Ye Sea Slugs!"

Surely sea-cucumber itself would be more valuable than cucumbers.

Yeah, but much less likely to be used as an example of a prosaic crime.

LH, LB: Robin Gill's books are awesome (although I don't have that one), but I had to spend like 15 minutes sifting through that stuff as it is! Weird that he didn't include the meaning "(regular) cucumber" in such a comprehensive list.

I think “Rise…” can very possibly be the most disorganized book I've ever read. It’s typeset by the author on MS Word, with plenty of things like underlined capitals and pages taken up almost entirely by footnotes. And it’s a mess! Hundreds of namako-themed haiku collected seemingly at random, good and bad and average, from everyone and everywhere, with multiple attempted translations for each one, interspersed with tiny essays on pretty much everything. It flows like a Mustang with triangle wheels on a rockbed. It’s glorious.

You actually make it seem so easy with your prsitneateon but I find this matter to be actually something which I think I would never understand. It seems too complex and very broad for me. I am looking forward for your next post, I’ll try to get the hang of it!