Wednesday, July 18, 2007

Common Paper Nauttilus, Cross-Barred Venus

The Common Paper Nautilus or Common Paper Argonaut is not really a shell in the true sense of the word. It is actually an egg case secreted by two arms of the female Argonauta argo (Linnaeus). Most shells will be secreted by the mantle of the mollusk, but not this one. I found this in the sargasso grass on Del Rey Beach, Florida on a recent trip there.
The animal is in the class Cephalopoda which is composed of the squid, octopus and nautilus. Most are predatory carnivores.
Only the female secretes the shell, the male Argonaut is much smaller and does not have a shell. They are usually found in tropic or temperate seas. The female can grow to the length of 2 feet and produce a shell as big as 14 inches long, these are nowhere near that size. They swim near the surface of the water and prey upon pteropod mollusks and small pelagic fish. Sailfish in turn, prey upon them.

Cross-Barred Venus, Chione cancellata (Linne) are one of the most plentiful shells on the island. They seem to come in a variety of colors depending on the sediment in their environment. They are heavy with strong, raised concentric ridges and rounded ribs that form a network of raised lines. Found in shallow waters, they are the main food source of the green and blue crab as well as moon snails. When you come across some with 'ready made holes for stringing', those have been likely drilled by the moon snail.
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