A prevailing hypothesis of microbial biogeography holds that all species are ubiquitous, but this may lead to fitting Pacific specimens into European taxa on the basis of light microscopy. There is now evidence of regional endemicity in freshwater diatoms in Australia and recent studies have shown large diversity in the Guam marine Licmophora flora. The aim was to compare Australian samples with Guam Licmophora spp., especially their girdle bands. Valves and girdle bands from samples collected from Australia and Micronesia were described from observations made via light and scanning-electron microscopy. Of the nine species present in Australian samples, six were previously undescribed. Species with unusual characters included Licmophora insolita Lobban & Emm.S.Santos sp. nov. with a novel location for the apical rimoportula and a Tharngan strip on the valvocopula; Licmophora ballerina Lobban & S.Blanco sp. nov., with distinctive 3rd and 4th pleurae; and the licmosphenioid Licmophora johnwestii Lobban & Emm.S.Santos sp. nov. Specimens resembling Licmophora debilis (Kütz.) Grunow and L. abbreviata C.Agardh, described from Europe, occurred in Great Barrier Reef samples. The study brings the Guam flora to 20 novel v. 2 matching Atlantic–European taxa. The proportion of new to known species in Australian and Guam samples suggests regional endemicity, at least being broadly different from European Licmophora floras.

We reviewed 9350 Australian species-level records and confirmed 64 species of the marine planktonic dinoflagellate genera Dinophysis Ehrenb. (17 species), Phalacroma F.Stein (12), Metaphalacroma L.S.Tai (1), Pseudophalacroma Jörg. (1), Ornithocercus F.Stein (7), Histioneis F.Stein (11 spp.), Parahistioneis Kof. & Skogsb. (4), Histiophysis (Kof. & Mich.) Kof. & Skogsb. (1), Citharistes F.Stein (2) and Amphisolenia F.Stein (8), from the period 1938–2019. The widespread D. acuminata Clap. & J.Lachm., D. acuta Ehrenb., D. caudata Kent, D. fortii Pavill., and D. tripos Gourret have attracted attention as causative organisms of diarrhetic shellfish poisoning in temperate Australian waters. We discriminate between Dinophysis and Phalacroma. We newly report from Australian waters O. assimilis Jörg., Metaphalacroma skogsbergii L.S.Tai, Parahistioneis pieltainii Osorio-Taffal, Amphisolenia extensa Kof., A. inflata G.Murr. & Whitt. and A. rectangulata Kof. We rediscovered Histiophysis rugosa (Kof. & Mich.) Kof. & Skogsb. here illustrated with two cells from the Coral Sea. The ornate tropical genera Ornithocercus and Histioneis are excellent warm-water indicators, reflecting the southward reach of the East Australian and Leeuwin currents, whereas D. truncata Cleve is a cold-water Subantarctic species.