No. 10–Still More on Whelks
The Florida horse conch and the four related species of whelk are not the only predatory snails here about. The former inhabitants of shells found on the beach with a round hole in them fell prey to the Moon Snail. Shark’s Eye is another common name for the species. The names no doubt come from the shape and coloration of the shell. They really are quite lovely in an understated way.
Feeding on both bivalves and other snails, the moon snail also has a proboscis with radular teeth which it uses to, first drill the hole, and then consume the hapless prey. An interesting fact is that during the drilling process an acid that breaks down calcium carbonate is secreted. In essence we have a snail with a hydraulic drill. Don’t be surprised to find a moon snail shell with a hole in it as they are equal opportunity predators.
The Banded Tulip is another predatory snail feeding on bivalves and other snails. There is also the Oyster Drill, growing to only an inch or so, which may be observed in association with oysters on low tide. As its name indicates, it drills holes in oysters to access its food.
Whelks may be found in a mating embrace on the beach in the spring. The larger of the two entwined is the female. With size varying relative to species, all large whelks are female and small ones male. Fact is, they change sex. In the knobbed whelk the transgender occurrence comes when the animals shell reaches six to seven inches in length.
A number of fish species, to include our local black sea bass, are also genetically programmed to follow this seemingly strange reproductive strategy. I haven’t seen the film but it’s my guess that Disney didn’t go down the road leading to the fact that Nemo’s dad is destined to become the mother of Nemo’s future step siblings.
Unfortunately dislodged from sub tidal holdfasts to be found washed up on both ocean beaches and estuarine shores, whelk egg cases are puzzlement to many who come across them. They may be recognized as a loosely coiled strand of individual leathery packets. In the case of the knobbed whelk, the tan colored strands may reach up to 18 inches in length when extended with packets the size of quarters throughout most of the length.
Each packet contains between 20 and 40 eggs of which roughly half are fertile. The infertile eggs are the food source for the developing whelks during the latter stages of gestation. At hatching the tiny (3 mm) whelks chew their way out of the natal chamber to begin life in a perilous world where the vast majority are taken by a variety of predators before they themselves are able to reproduce.
Calcium carbonate, mentioned earlier, is a constituent of sea water which is metabolized and secreted by all shelled mollusks in the shell building process. Observe the surface of a clam. You will clearly see the layers of accretion radiating outward from the hinge area. The spiral effect you see when observing the crown of a whelk shows they build around and around a central core beginning at the point at the center of the crown. That point is the original 3mm post natal shell where it all began.
In the past three columns we have only touched the surface of the world mollusks all too easily dismissed as mundane by the uninformed. To paraphrase the bard most loosely, “There is more beneath the tides, Horatio, than is dreamt of in your wildest imaginationings.”