Do not pick an opihi as big as a quarter.

I wrote last week it's legal to take opihi that size, but that's too small. Several readers pointed out (some kindly, some not so) a quarter is just under an inch in diameter, and the smallest opihi that may be taken by law is 1 1/4 inch.

Such a little difference might seem like no big deal, but an opihi the size of a quarter is too small to reproduce. And even when its shell is 1 1/4 inches wide, the little snail inside is just getting started making more of its kind.

The bigger we let these snails grow before plucking them from their rocks, the more offspring they'll have, and then the more pupus we'll eat.

People in other parts of the world will wonder what I'm talking about, but Hawaii residents know all about these snails — and about pupus, a Hawaiian word meaning both snails and snacks. Even residents who've never seen or eaten an opihi know them from news reports. While collecting, opihi pickers sometimes get swept to sea and drown.

Ancient Hawaiians referred to opihi gathering as he ia make, meaning a creature that could cause death.

The three edible species that grow here are endemic to the islands and hold a place of honor in the Hawaiian culture. Opihi are standard fare at traditional feasts.

Opihi are limpets, snails with protective shells that look like pointy hats and have ridges and grooves running from the tip to the edges. The snail's soft body, consisting of a head with two tentacles, two eyes, a mouth and a muscular foot for clinging and crawling, is almost completely hidden beneath.

Opihi graze on algae that grow on wave-washed rocks. Home base is a circle the snail scrapes in the rock with its filelike tongue.

The shell's edges have an airtight fit in this home depression, allowing the opihi to keep from drying out during low tide. During unusually hot periods some Hawaii species lift their shells slightly to cool off.

Opihi reproduce by spewing their eggs and sperm into the water, most of which become morsels of food for other animals. Nature, however, is a great matchmaker, and some sex cells connect. The resulting larvae drift for only three or four days, and then the tiny opihi find their own rock and settle down.

When I moved to Hawaii in the early '80s, I often found empty opihi shells lying among the rocks, discarded by opihi aficionados who ate the snails on the spot.

The insides of opihi shells are smooth mother-of-pearl, and I loved, and collected, these little jewel-lined hats. But they weren't tiny. Most were well over the 1 1/4 -inch limit.

I admired my opihi shells so much, a friend gave me an opihi lei, the large shells glued face to face and the outsides polished to a glossy shine.

All my shells are true treasures now because as the snails became scarcer, the picking got fiercer, and people took small ones before they could reproduce.

Today, Hawaii's opihi are rare except in dangerous wave-splashed areas.

After readers pointed out my mistake, I did an Internet search, and up popped two of my own “;Ocean Watch”; columns, one from 1996, the other from 2003, both informing me the smallest opihi shell you can take is 1 1/4 inches in diameter.

I won't forget that number again. Nor will I forget the size of a quarter.

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