main channel separating the two mangrove islands constituting the Twin Cays, off Belize, Caribbean Sea (16°50'N, 88°06'W; 16.8333°, -88.1°); 2.25 m, in mucus tubes adorned with miscellaneous debris and attached to the blades of turtle grass (Thalassia testudinum) growing in a mixture of coarse and fine mainly calcareous sediment with varying amounts of mangrove detritus