Observations on two melobesioid crustose coralline red algal species from the British Isles: Exilicrusta parva, a new genus and species, and Lithothamnion Sonderi Hauck

Abstract

A new genus, Exilicrusta, and species, E. parva, of crustose coralline Rhodophyta are described from the British Isles. Exilicrusta has multiporate tetrasporangial conceptacles and cell fusions and therefore pertains to the subfamily Melobesioideae. It has a dimerous thallus like the genus Melobesia but differs in gametangial/carposporangial reproductive features. Exilicrusta parva is found growing together with Lithothamnion sonderi and both species have flared epithallial cells, as have all species of Lithothamnion. Exilicrusta differs from Lithothamnion, however, in having a dimerous as opposed to a monomerous thallus, and in the structure of its gametangial/carposporangial reproductive bodies. Lithothamnion sonderi is compared with its holotype specimen.