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The Collaborative International Dictionary
Sea fir

Sea fir \Sea" fir`\ (Zo["o]l.) A sertularian hydroid, especially Sertularia abietina, which branches like a miniature fir tree.

Wiktionary
sea fir

n. A sertularian hydroid, especially (taxlink Sertularia abietina species noshow=1), which branches like a miniature fir tree.