Heliophyllum, genus of extinct coral found as fossils in Devonian marine rocks (the Devonian Period began 416 million years ago and lasted about 56 million years). Heliophyllum was a solitary animal rather than a colonial form. The distinctive laminated form of its structure is clearly periodic, its growth being a function of time; this factor has been employed to calculate the length of the Devonian day and year. Several species of Heliophyllum are known.

This article was most recently revised and updated by John P. Rafferty.
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