Night dive - started OK, though a Texan couple had problems descending - they turned out to be a total liability - bad buoyancy, crowding (hit me in the back of the head, etc.). Saw some good invertebrates - donkey dung sea cucumeber (2ft+), some very big crabs, & a big spotted drum & several morays. Then nightmare couple ascended with Errol (dive leader). Protocol was that we chould stay down and wait for Errol to find us, but after a minute with Melissa & Russell, no sign, so we ascend. We were already at 5.5m, so had finished safety stop. No sign on surface, so we decide to head back to shore. I'd assumed at surface, but Russell suggests at depth. Melissa agrees, as long as not too deep. We head back, but find ourselves in dead end, and ascend. Melissa hopping mad with Russell (they got married 2 days ago, too!) and says we should continue at surface. He forces issue, & we descend. I'd have gone with her [view], but couldn't interfere in spat! Main point of dive: saw "The Thing" - small one (?) - multi-segmented invertebrate, native to St Lucia.