si1-ham1 (short a) = 螄蚶 = cockles
What a wonderful asset you are to the Forum. Indeed, those pictures are all of si-ham, so I guess you've solved the mystery of the origin of the "si". Thanks a lot!
Anyway, I think (some of) you guys are lucky that your parents made ô'ácian at home.
In my youth in Malaysia, there were heaps of dishes which people would usually not cook at home, but only ever eat by going to a hawker stall - o-cien being one of them. Part of the reason my parents do it is because they migrated to Australia, where all these yummy dishes were no longer readily available (in the 70's, a lot of them - particularly the S.E. Asian as opposed to the Cantonese ones - wouldn't even have been available in Sydney Chinatown, let alone the remote country town that we moved to***). So my parents had to learn to cook such dishes themselves. And, in the now almost unimaginable days before Wikipedia and Youtube and Google, my parents often had to "guess and experiment" with the ingredients and recipes until they got it right! We even had to make our own tofu, from the powered stuff in small cardboard boxes. The taste and texture were pretty awful, but hey, we were at least able to eat "tofu"!
***: In fact, when we moved there, the (two) Chinese restaurants in town had only 2 forms of noodle soup, massively adapted for the Anglo-Saxon tastes of the time. They were called in the local language "long soup" (egg noodles in soup, with one or two wisps of vegetable) and "short soup" (wan-tan in soup, with one or two wisps of vegetable). I doubt if these terms are even *known* in the vastly more multi-cultural, culinairily sophisticated Australia of today... I can't know for certain, but I've always assumed that the "long" referred to the fact that 'noodles are long', while "short" referred to the fact that 'wan-tans are roundish, i.e. not long'.
PS. I know the name "tang-o" from my childhood, but have little memory of the taste nor look. Do you know the scientific and/or English name of it?
PPS. After writing the above, I tried googling, and both "Chinese" + "long soup" and "Chinese" + "short soup" produced 10,000+ hits, many of them .au sites (with recipes which reflect my description), so apparently, the terminology has lived on. I can't imagine any of my younger Australian friends using this term though - it has such a ring of the old, "anglo-celtic based" Australia to it. Ah-bin: have you come across these terms in your time there?