The Jurassic Lithocodium aggregatum - Troglotella incrustans foraminiferal consortium.-
Palaeontology, 39, 21-52, Oxford.
Lithocodium aggregatum, an enigmatic micro-encruster widespread in Mesozoic shallow marine carbonates, was considered to be a codiacean alga but can now be identified from Upper Jurassic examples as loftusiid foraminifer (Order Lituolida, Superfamily Loftusiacea). The microgranular wall may also contain detrital quartz, a feature which excludes any codiacean affinity. The complex, alveolar though imperforate, wall structure is identical to that of other loftusiid foraminifers; the only difference is the encrusting life habit of Lithocodium. The foraminifer is coiled in juvenile growth stages but subsequently developed irregular growth, making it possible for it to contribute to the formation of oncoids and reefal biotic crusts. The numerous alveolar structures, which are covered by only a very thin outer wall, suggest that these alveoli were containers for photoautotrophic symbionts. Lithocodium and Bacinella are not parts of one single organism, although phrenotheca-like structures crossing parts of the chambers partly resemble the latter. In the Upper Jurassic material, nearly every specimen of Lithocodium includes bubble-like structures, formerly interpreted as algal sporangia. These structures are identified here as the foraminifer Troglotella incrustans. During its later growth, Troglotella developed an irregular shape and grew into the alveoli of the Lithocodium walls. This may be interpreted as a commensal relationship, with Troglotella feeding on the carbohydrates synthesized by the Lithocodium symbionts.