Fossil specimens of two semi-endophytic species of Lithophyllum, L. kenjikonishii sp. nov. and L. cuneatum (Corallinaceae, Rhodophyta), were discovered in thin sections of ocean floor cores of the last deglacial period (c. 20,000-10,000 years before present) obtained from Tahiti, French Polynesia, during Expedition 310 of the Integrated Ocean Drilling Program. Detailed morphological-anatomical accounts of both species are provided, and their placement in Lithophyllum and the subfamily Lithophylloideae is discussed in relation to recent classification proposals. Lithophyllum kenjikonishii, recorded only from fossil thalli, and L. cuneatum, known from fossil and nonfossil thalli, are readily distinguished in tetrasporangial conceptacle pore canal anatomy and on differences in spermatangial conceptacle chamber anatomy. Both species are semi-endophytic in Hydrolithon onkodes, another species of Corallinaceae. Taphonomic signatures evident in thin sections suggest that the occurrence of L. kenjikonishii, L. cuneatum, or Hydrolithon braganum (another semi-endophyte) growing in H. onkodes may be a reliable reference for identifying shallow-water settings (fore reef, reef flat and lagoon) in coral reef depositional systems within Pleistocene to last deglacial sedimentary successions in the Pacific Ocean. Taphonomic signatures thus have considerable potential as a palaeoecologic proxy in interpreting reef growth history.
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