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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 ?
Thermochemical Destruction of Graptolite Argillite.
Phylogenetic analysis reveals that Rhabdopleura is an extant graptolite. Lethaia 46: 34-56.
Between the Cambrian sand- and siltstones and Ordovician limestones occur the major sources of Rn: Lower-Ordovician obolus sandstone with P-rich layers of phosphorite that are overlain by graptolite argillite.
There is currently some confusion as to the definition of the base of the Amorphognathus tvaerensis Zone, and also regarding its relationship to the graptolite biozonation and to the base of the Upper Ordovician Series.
Geochemical heterogeneity of Estonian graptolite argillite.
Graptolite age control for the Llandovery-Wenlock Sangerville and Ludlow Smalls Falls formations in central Maine also constrains the ages of the intervening Perry Mountain and overlying Madrid formations (Table 2; Ludman and Griffin 1974; Pankiwskyj et al.
The boundary level coincides with the first appearance of the graptolite Diplacanthograptus caudatus (Lapworth), which is known from Australasia, Eastern North America, South Central USA, Scotland, Newfoundland (Goldman 2003), but not from the East Baltic.
In addition, graptolite colonies are believed to have had determinate growth leading to distinct species-specific forms and sizes (Mitchell, 1988).
In Proceedings of the 6th International Graptolite Conference (GWG-IPA) & 1998 Field Meeting, IUGS Subcommission on Silurian Stratigraphy (Gutierrez-Marco, J.
Available geological data indicate that the Lower Silurian graptolite shales represent the most prospective source rock body for shale gas exploration in west Lithuania.