Corallina officinalis Linnaeus
Cúnach Trá (Gaeil.)
Description: Whitish-pink to lilac, calcified, articulated fronds, 60-70 (-120) mm high, axis cylindrical to compressed, repeatedly pinnate from and expanded discoid base, branchng often irregular. Growth form very variable, often stunted. In unfavourable habitats erect system vestigial, but extensive base may be present.
Habitat: On rock, midtidal pools and drainage runnels, lower intertidal and shallow subtidal, widespread and abundant, especially on exposed coasts.
Similar species: Jania squamata, a rare and beautiful species in Ireland and Britain found in wave-exposed, lower-shore rock pools, has shield-shaped articulations and can be difficult to distinguish from C. officinalis. Ellisolandia elongata is smaller and more regularly branched; the recently described species Corallina caespitosa is more caespitose, very small, and has strongly compressed terminal articulations.
Hippolyte leptocerus (Heller, 1863), a prawn, has evolved a very effective camouflage for living on Corallina. The picture below shows a specimen about 10 mm long, taken by Dave Fenwick (http://www.aphotomarine.com ) in Cornwall.