- Kingdom: Plantae
- Phylum: Rhodophyta
- Class: Florideophyceae
- Order: Corallinales
- Family: Hapalidiaceae
- Scientific name: Lithothamnion glaciale
- Norwegian: vorterugl
It is virtually impossible to identify the different species of mearl from photographies alone. L. glaciale is perhaps the most common species in Norway. It starts of as a deep pink crust on a hard substrate. After a while small excrescences start to grow, and eventually become nodules or branched structures. Loose noodles are often found on the seabed in the subtidal zone, where they continue to grow, even if they are continuously grinded by the movements caused by current or waves.
It may be confused with two other, not so common, species, L. corallioides and Phymatolithon calcareum. They have thinner (2-3 mm), more fragile branches.
Grow on any hard substrate from the tidal zone and down to 70 meters. Eventually they may be torn loose and found laying on the seabed.
It is known from both sides of the North Atlantic Ocean, as well as in the North-Western Pacific Ocean.