Remarks on West Pacific Nummulitidae (foraminifera)

Living Nummulitidae achieve their highest diversity in the subtropical and tropical West Pacific. Although all house symbiotic microalgae, they avoid highly illuminated areas near the water surface, since their flat tests cou ld be easily damaged by the hydrodynamic regime. The preference for calm wa ter conditions extends their depth distribution down to the base of the pho tic zone. West Pacific Nummulitidae can be differentiated into ten species belonging to six genera according to an ecological species concept. The gen us Operculina d'Orbigny is represented by three species. While O. discoidal is (d'Orbigny) prefers a fine-grained bottom under medium light conditions (10% surface intensity), 0, ammonoides (Gronovius) prefers a coarser substr ate and sometimes can be found on hard bottoms. Light dependence ranges fro m 1.5% to 68% surface intensity. Less illuminated coarse sands are inhabite d by Operculina cf, 0, complanata (Defrance), which is the dominant symbion t-bearing foraminifer between light intensities of 0.2% to 12% surface illu mination, The genus Planostegina Banner and Hodgkinson demonstrates transit ions to the genus Operculina in test form and surface, while the division i nto chamberlets is similar to Heterostegina. Planostegina operculinoides (H ofker) is distinguished by flat tests and delicate chamberlets, It lives on sandy bottoms restricted to light intensities between 0.45% and 26% surfac e illumination. The more robust Planstegina aff. P, operculinoides (Hofker) prefers light intensities between 0.4% and 2.7% surface illumination, Plan operculina heterosteginoides (Hofker) shows morphological transition to Ope rculina cf, 0, complanata in developing incomplete septula. This species li ves in low illuminated areas (0.3% to 2.5% surface intensity) and prefers m edium to fine-grained sands. Heterostegina depressa d'Orbigny spans a broad range in light intensities (2% to 70% surface illumination), and is protec ted against irradiation by thick tests and a cryptic life mode near the sur face. Test construction enables life under strong hydrodynamic regimes. Thi s species lives firmly attached to hard substrates, thus counteracting tran sportation by water movement. Nummulites venosus (Fichtel and Moll) differs from H, depressa in having undivided chambers. It lives exclusively on coa rse sand and avoids high sediment movement, thus starting its distribution beneath the fair weather wave base. According to light intensities, the upp er limit may be similar to 0, ammonoides (80%), while the lower limit is 2. 5% surface illumination. Operculinella cumingii (Carpenter) inhabits coarse to medium sand in deeper regions between 1.2% and 25% surface illumination , Tests of the cyclic, large-sized species Cycloclypeus carpenteri Brady ar e easily transported due to the thin, plate-like form. The upper distributi on limit correlates with the storm wave base, restricting C, carpenteri to depths below 50 m, The lower distribution limit depends on light intensity and is located near the base of the photic zone (0.4% surface illumination) .