Three new Licmophora species (Bacillariophyta: Fragilariophyceae) from Guam, two with an axial wave in the valve

Abstract Background Diatoms in genus Licmophora are found as epiphytes on marine shores and are members of fouling communities. They can be abundant on natural coral reef substrates such as filamentous algae and as fringes on Halimeda. Biodiversity of benthic tropical diatoms is generally poorly known. Several new species of Licmophora have been reported from Guam but many are still undescribed. Methods Samples of seaweeds with evident diatom coatings were collected during scuba dives, examined live, preserved in formalin, and processed with nitric acid cleaning following standard practice. Cleaned samples were examined in LM and SEM. Results We describe two species unusual in having an axial wave in the valve, and a further long, straight species. L. repanda n. sp. and L. undulata n. sp. were of similar lengths (ca. 200 μm long) and both had axial waves but L. undulata was more slender with an inflated basal pole, had colonies on mucilage pads vs. long, single-stranded mucilage stalks. In addition, L. undulata had one apical rimoportula vs. two, elongated areolae along the midrib vs. uniform areolae, and the valvocopular advalvar striae ended halfway along, whereas in L. repanda they continued to the end. L. joymaciae n. sp. grew on long, single-stranded mucilage stalks with valves 300–400 μm long, with two apical rimoportulae, and basal pole not inflated. As in L. undulata its valvocopular advalvar striae ended halfway along the band. Stria densities were different at apex vs. base in L. joymaciae but not in the two wavy species. In all species, the 4th pleura had an apical cap and a narrow band with a single row of pores but it was larger in L. joymaciae. The other three girdle bands did not present any major differences among the three species but are documented for future comparisons with other species. Conclusions Although the morphometric differences are small among the new species and between them and similar known species, the combinations of character states clearly shows that they are different.