Gomphotheca marciae (Bacillariophyceae: Bacillariaceae), a new species in a rarely seen genus

Specimens of an extremely long, heteropolar nitzschioid diatom from mud scraped from mangrove pneumorrhizae on two Micronesian islands were identified as a new species of Gomphotheca. This genus contains two other, rarely seen species, only one of which has been observed with SEM. Our SEM images showed that G. marciae n. sp. is structurally similar to G. sinensis, with very long, heteropolar, cuneate cells with a central keel and internal costate fibulae, and thick, chambered copulae with contrasting external and internal pore patterns. However, the raphe path of G. marciae lacks a central break, conopea are present along each side of the keel, the fibula height is different, pseudosepta are present at both poles, while valve cross section and stria density also differ. We also report the presence of single-walled pleurae.