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Trigonia
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Sea otter (Enhydra lutris), also called great sea otter, rare, completely marine otter of the northern Pacific, usually found in kelp beds. Floats on back. Looks like sea otter laughing. saltwater otters
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Trigonia

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Trigonioida

Trigonia, genus of mollusks that first appeared during the Jurassic period, which began about 208 million years ago. The still-extant Trigonia has a triangular shell with distinctive concentric ridges on its surface as well as nodular outgrowths. A different ornamental pattern is present in the posterior parts of the shell.