Thoracochaete zosterae. One of my favourite flies. For what reason I can't say, but I do like the lesser dung flies and this little beachcomber is "lovely". Note the gentle sweep of the inward pointing thoracic spines. Poetry in motion. There must be some historic reason why I connect to this species but I can't say what it is.
This was one of many under a rock with sandhoppers and sea slaters (but sadly not Strigamia maritima on this occasion)