MORPHOLOGY AND PALAEOECOLOGY OF NEW, NON-MARINE MICROCONCHID TUBEWORM FROM LOWER CARBONIFEROUS (UPPER MISSISSIPPIAN) OF WEST VIRGINIA, USA

摘要

A new species of a non-marine microconchid (Tentaculita) tubeworm, Microconchus hintonensis , from the Lower Carboniferous (Upper Mississippian, Chesterian) of West Virginia, USA, is described. Non-marine microconchids occur abundantly in the deposits of the Bluefield, lower Hinton, Princeton and Bluestone Formations of the Mauch Chunk Group, where they are either associated with land plant remains and bivalve shells, or are preserved loose in the host sediment. The specimens attached to plant remains and bivalve shells, are poorly preserved, but those occurring loose in the deposits are well-preserved in three dimensions. The interpretation pre sented here, is that the loose specimens of Microconchus hintonensis sp. nov. also originally encrusted plants (land plants, algae) and bivalve shells, but became detached after substrate degradation and dissolution. The association of land plant remains, charophyte gyrogonites, bivalves, ostracodes, conchostracans, and fish teeth and scales, and the concomitant lack of strictly marine fossils indicate that the microconchid-bearing deposits of the lower Hinton, Princeton and Bluestone Formations were deposited in fresh-water environments. Microconchus hintonensis sp. nov. is regarded as a highly fecund, opportunistic species that in large numbers colonized every available substrate in its habitat. Its abundance in the deposits investigated indicates that the species was welladapted to the environments it occupied, even during episodes of higher sedimentation rates and/or competition with other soft-bodied encrusters. During such episodes, microconchids were able to grow vertically by uncoiling and elevating their tubes, in order to escape potential burial and/or overgrowth by other encrusters.