Clathromorphum circumscriptum

Clathromorphum circumscriptum is a species of crustose coralline red algae found in cold-water marine environments, particularly in the Arctic and subarctic regions. It grows by depositing annual layers of calcium carbonate, creating a hardened skeleton that can persist for centuries.

Clathromorphum circumscriptum and related species in the genus are among the longest-lived organisms on Earth, with some individuals persisting for centuries. Species like Clathromorphum compactum, a close relative, have been documented living for several hundred years or more.

Like other coralline algae, Clathromorphum circumscriptum deposits calcium carbonate in its cell walls as it grows, creating distinct annual growth bands similar to tree rings. Scientists can read these layered crusts to reconstruct past ocean conditions, including temperature and sea-ice cover.

This species grows in cold-water marine environments across Arctic and subarctic regions of the North Atlantic and North Pacific. It attaches to rocky substrates in subtidal and lower intertidal zones where cold, nutrient-rich waters support its slow calcified growth.