|
Nucula Sulcata
''Nucula'' is a genus of very small saltwater clams. They are part of the family Nuculidae. Fossil records This genus is very ancient. Fossils are known from the Arenig to the Quaternary (age range: from 478.6 to 0.0 million years ago). Fossils are found in the marine strata all over the world. Description Shells of species within this genus can reach a size of about . They are equivalve, symmetrical, approximately triangular. The surface has fine concentric growth lines. These clams live in the muddy sand close to the sediment surface at a depth of 20 to 200 meters. Species Nowadays there are still many species of this genus, which have had virtually no change in the course of time. Species within the genus ''Nucula'' include: * '' Nucula annulata'' Hampson, 1971 * '' Nucula atacellana'' Schenck, 1939 - cancellate nutclam * '' Nucula austrobenthalis'' Dell, 1990 * '' Nucula beachportensis'' Verco, 1907 * '' Nucula benguelana'' (A. H. Clarke, 1961) * '' Nucula brasilian ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arenig
In geology, the Arenig (or Arenigian) is a time interval during the Ordovician period and also the suite of rocks which were deposited during this interval. History The term was first used by Adam Sedgwick in 1847 with reference to the "Arenig Ashes and Porphyries" in the neighbourhood of Arenig Fawr, in Merioneth, North Wales. The rock-succession in the Arenig district has been recognized by W. G. Fearnsides (“On the Geology of Arenig Fawr and Moel Llanfnant", Q.J.G.S. vol. lxi., 1905, pp. 608–640, with maps). The above succession is divisible into: # A lower series of gritty and calcareous sediments, the "Arenig Series" as it is now understood; # A middle series, mainly volcanic, with shale, the "Llandeilo Series"; and # The shale and limestones of the Bala or Caradoc Stage. It was to the middle series (2) that Sedgwick first applied the term "Arenig". In the typical region and in North Wales generally the Arenig series appears to be unconformable upon the Cambrian ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
