A novel 330 nm UV absorbing compound, a methylamine substituted mycosporine (1), was isolated from methanol extracts of two hermatypic scleractinians. Structural elucidation yielded the molecular formula C₁₃H₂₂N₂O₆. This was given the trivial name Mycosporine-methylamine:threonine. Mycosporines are amino acids or reduced amino acid derivatives of one of two common ring systems, an aminocyclohexenone and an aminocyclohexenimine. These small water soluble compounds absorb strongly in the 310-360 nm ultraviolet region. Widely distributed among fungi, and marine plants and animals, it has often been suggested that they may provide protection from UV radiation damage. As yet there is little specific evidence about their biochemical roles in-vivo. To date, all reported imino-mycosporines possess a glycine substituent. This is the first example of an imino-mycosporine that does not contain glycine, but has a methylamine group not previously identified with any mycosporine. Also presented in this communication is the assignment of ring carbon shifts that have so far only been reported as interchangeable between (C1,C6) and (C3,C4).