What is a genus of deep-sea alcyonaria consisting of a cluster of large flowerlike polyps situated at the summit of a long, slender stem which stands upright in the mud, supported by a bulbous base called?

umbellularia — A genus of deep-sea alcyonaria consisting of a cluster of large flowerlike polyps situated at the summit of a long, slender stem which stands upright in the mud, supported by a bulbous base. (Webster's 1913.)

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