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Inner Margin (inner + margin)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

Heliodiaptomus phuthaiorum n. sp., a New Freshwater Copepod (Calanoida, Diaptomidae) from Temporary Ponds in Northeast Thailand

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 4 2004
La-orsri Sanoamuang
Abstract An illustrated description of a new species, Heliodiaptomus phuthaiorum n. sp., from nine of the 456 sampled localities in northeast Thailand, is presented. Morphologically, it is closely related to the Indian H. pulcher (Gurney, 1907). The new species is characterized in the male by the prominent, spinulose knob on the inner margin of the right basis; the finely serrated inner margin of the right second exopodite-segment; and the extraordinary large, tongue-like projection on proximal inner margin of the left basis. In the female, the genital somite is unusually long, much longer than the other two urosomites combined. This new species is rare and has been found only in temporary ponds in Nakhon Pranom and Nong Khai Provinces. It usually co-occurs with 1,5 other diaptomids; the most frequently co-occurring species are Neodiaptomus blachei (Brehm, 1951), N. yangtsekiangensisMashiko, 1951 and Eodiaptomus phuphanensisSanoamuang, 2001. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Cenozoic stratigraphy and subsidence history of the South China Sea margin in the Taiwan region

BASIN RESEARCH, Issue 4 2003
A. T. Lin
Seismic reflection profiles and well data are used to determine the Cenozoic stratigraphic and tectonic development of the northern margin of the South China Sea. In the Taiwan region, this margin evolved from a Palaeogene rift to a latest Miocene,Recent foreland basin. This evolution is related to the opening of the South China Sea and its subsequent partial closure by the Taiwan orogeny. Seismic data, together with the subsidence analysis of deep wells, show that during rifting (,58,37 Ma), lithospheric extension occurred simultaneously in discrete rift belts. These belts form a >200 km wide rift zone and are associated with a stretching factor, ,, in the range ,1.4,1.6. By ,37 Ma, the focus of rifting shifted to the present-day continent,ocean boundary off southern Taiwan, which led to continental rupture and initial seafloor spreading of the South China Sea at ,30 Ma. Intense rifting during the rift,drift transition (,37,30 Ma) may have induced a transient, small-scale mantle convection beneath the rift. The coeval crustal uplift (Oligocene uplift) of the previously rifted margin, which led to erosion and development of the breakup unconformity, was most likely caused by the induced convection. Oligocene uplift was followed by rapid, early post-breakup subsidence (,30,18 Ma) possibly as the inferred induced convection abated following initial seafloor spreading. Rapid subsidence of the inner margin is interpreted as thermally controlled subsidence, whereas rapid subsidence in the outer shelf of the outer margin was accompanied by fault activity during the interval ,30,21 Ma. This extension in the outer margin (,,1.5) is manifested in the Tainan Basin, which formed on top of the deeply eroded Mesozoic basement. During the interval ,21,12.5 Ma, the entire margin experienced broad thermal subsidence. It was not until ,12.5 Ma that rifting resumed, being especially active in the Tainan Basin (,,1.1). Rifting ceased at ,6.5 Ma due to the orogeny caused by the overthrusting of the Luzon volcanic arc. The Taiwan orogeny created a foreland basin by loading and flexing the underlying rifted margin. The foreland flexure inherited the mechanical and thermal properties of the underlying rifted margin, thereby dividing the basin into north and south segments. The north segment developed on a lithosphere where the major rift/thermal event occurred ,58,30 Ma, and this segment shows minor normal faulting related to lithospheric flexure. In contrast, the south segment developed on a lithosphere, which experienced two more recent rift/thermal events during ,30,21 and ,12.5,6.5 Ma. The basal foreland surface of the south segment is highly faulted, especially along the previous northern rifted flank, thereby creating a deeper foreland flexure that trends obliquely to the strike of the orogen. [source]

Ultrastructure and development of forked and capillary setae in the polychaetes Orbinia bioreti and Orbinia latreillii (Annelida: Orbiniidae)

INVERTEBRATE BIOLOGY, Issue 1 2001
Bilke Hausam
Abstract. Recent investigations into chaetogenesis of certain types of annelid setae provide important results for unravelling the phylogenetic relationships within several taxa of poly-chaetous annelids. This paper presents data on ultrastructure and development of 2 types of orbiniid setae. The analysis of the crenulate capillaries in Orbinia latreillii reveals a formation process which clearly differs from the development of Equisetum -like setae of lingulid bra-chiopods. For the investigation of forked setae, which up to now have been neglected in the discussion on the phylogenetic significance of annelid setae, notopodial setal sacs of O. latreillii and O. bioreti were studied by light- and electron microscopy. In the setal sacs, stages of forked setae are restricted to a dorsocaudal pouch, which represents the site of setal formation. The 2 diverging, stout tines of the fork bear spines on their inner margins, each of which is preformed by a single microvillus. After retraction of the microvilli, a characteristic pattern of the setal canals inside of the spines remains. The present study belongs to a series of comparative studies into chaetogenesis of forked setae. These special setae are also found in other orbiniid taxa as well as some paraonids, scalibregmatids, and nephtyids. Ultrastructural investigations into the development of these forked setae might suggest homology. [source]