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The trace fossil, Ophiomorpha nodosa Lundgren, callianasid burrows, and other similar decapod domichnia exhibit petrographically distinct wall structures that are formed by the mandibular activities of the decapods during construction of their tubular domiciles. These decapod burrows are lined with one or two layers of aggregated sand pellets, 1-10 mm in diameter. The pellets, in turn, are composed of radially oriented, 0.025-0.5-mm subspherical masses of sand grains in a fine-grained, organo-clay matrix.
Callianasid decapods live and construct ophiomorphid burrows in a wide range of marine and brackish-water environments, including estuaries, bays, lagoons, tidal pools and creeks, beaches, shallow-littoral deposits, and in sediments at least 1.5 km offshore at depths of at least 12 m. Ophiomorphid burrows of Callianasa major and C. atlanticus average only about 5 burrows/sq m in the high-energy, open-marine shore zones and increase to an average of 20 burrows/sq m in 10 m of water, 1 km offshore. The highest concentrations of actively used ophiomorphid burrows, up to 450/sq m, are in the protected, low-energy, tidal pools of the bay and lagoon shores. Contrary to previous reports, callianasid burrows and their ancient equivalents, Ophiomorpha nodosa Lundgren, are not indicators of the high-energy, open-marine littoral zone.
Callianasa major and C. atlanticus burrows extend down, vertically, to depths of 4.7 m below the sediment surface, where they branch laterally as interconnected, horizontal gallery systems of wide extent. Identical configurations of Ophiomorpha nodosa Lundgren are present in the Gulf Coastal Plain Mesozoic and Cenozoic sediments.
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