bi·o·herm 
(bīō-hûrm′)
(bīō-hûrm′)n.
A massive, usually mound-shaped structure found in sedimentary rock strata, produced by the accretion of organic carbonate by a variety of marine invertebrates, such as corals and mollusks, and algae.
[BIO- + Greek herma, sunken rock, reef (of unknown origin).]