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see HemichordataHemichordata
, small phylum of marine invertebrates closely related to both the echinoderms (phylum Echinodermata) and chordates (phylum Chordata). Acorn worms, class Enteropneusta, are the most common hemichordates.
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References in periodicals archive ?
Alum shale, as well as graptolite argillite, contains remarkably high concentrations of trace metals such as U, Mo, V and Ni, but may also be locally enriched with rare earth elements (REE), Cd, Au, Sb, As, Pt [7].
The upper parts of the Bear River formation in the northwestern area and Feltzen formation in the southeastern areas locally contains the Early Ordovician graptolite Rhabdinopora flabelliformis, suggesting that the underlying Acacia Brook, Cunard, Bloomfield, and Moshers Island formations are Middle to Late Cambrian, and that a significant unconformity exists between the Halifax Group and the overlying Silurian White Rock Formation.
The boundary between the Hunneberg and Billingen "groups" (later referred to as stages, substages or series) was placed between the Megistaspis (Paramegistaspis) planilimbata and Megalaspides dalecarlicus trilobite biozones when established (Tjernvik 1956), coinciding with the lower boundary of the Phyllograptus densus graptolite Biozone.
Major and minor elements in Estonian graptolite argillite.
Accordingly, this cosmopolitan graptolite is used as the main correlation criterion for the boundary of the Fifth Stage as well as the Upper Ordovician Series worldwide (e.
As was mentioned above, in the study area the main sources of high Rn concentrations in soil air are the Lower-Ordovician U-rich rocks, graptolite argillite, and obolus sandstone (phosphorite), and among the Quaternary deposits, clasts and fines of the above-mentioned rocks and to a lesser extent the Quaternary deposits enriched with erratic granitoid material of the rapakivi formation.
Patterns and processes of latest Ordovician graptolite extinction and recovery based on the data from South China.
Understanding the paleoclimate of the Rheic Ocean at the beginning of the Mississippian Period, throughout the Kinderhookian, will help determine the spatial and temporal limits of the dendroid Graptolite Dictyonema within Missouri.