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Overall benthic macroinvertebrate biodiversity, along with laternulid density, was higher closer to mangroves but relative infaunal invertebrate dominance increased along a transect that transcended a hummock closer to the mangrove forest, across an open sand fl at, and terminated in another isolated humMock farther from the fringing forest. A population of the anomalodesmatan bivalve Laternula truncata (Lamarck, 1818) was examined in a mangrove sand fl at in Kungkrabaen Bay, Thailand, to determine population size, cohort distribution, and basic relationships with sediment and infaunal macroinvertebrate biodiversity. Relatively high densities of L. truncata were found in muddy sands, often deeply buried in or close to tangled rootlet mats of the mangrove trees Avicennia alba Blume, 1827, and A. marina (Forsskal) Vierhapper, 1907, along isolated mangrove hummocks. They were less common in open areas of the mangrove fl at. This population of L. truncata was relatively evenly distributed across size classes, minus the smallest sizes, suggesting continuous recruitment with a possible loss of recent recruits or recruitment. Overall benthic macroinvertebrate biodiversity, along with laternulid density, was higher closer to mangroves but relative infaunal invertebrate dominance increased along a transect that transcended a hummock closer to the mangrove forest, across an open sand fl at, and terminated in another isolated hummock farther from the fringing forest. A nearby population of L. cf. corrugata (Reeve, 1863) inhabited a distinctly different habitat. Laternula cf. corrugata was shallowly buried and dwelt in the mangrove forest proper among different species of mangroves and in sandier sediments. Behavioural observations of both laternulids indicated that both were capable of reburying, with smaller specimens more rapidly, albeit still slowly, succeeding in full re-entry into the sediment. Larger specimens of L. truncata were incapable of reburial. Morphological, ecological, and behavioural distinctions between L. truncata and L. cf. corrugata are considered in light of their habitat differences, confusion within laternulid systematics, and diffi culty in resolving the taxonomy of the latter species.