15,140 research outputs found
Resurrection of the sea pen genus Ptilella Gray, 1870 and description of Ptilella grayi n. sp. from the NE Atlantic (Octocorallia: Pennatulacea)
The order Pennatulacea covers a group of specialized and morphologically distinct octocorals found in all oceans from intertidal areas to more than 6000 m in depth. Sea pens constitute an important structural component in marine soft-bottom communities by increasing the complexity of these environments. Despite being both morphologically distinctive and ecologically important, the taxonomy and systematics of sea pens is still poorly understood. Recent molecular studies have shown the existence of convergent morphological features, making the current familial distribution of genera unstable. The genus Pennatula Linnaeus, 1758 was one of the first described octocoral genera. It is the type genus of its family, Pennatulidae. Colonies of this genus have a characteristic morphology. Recent sampling efforts in the northeastern Atlantic have provided a number of colonies initially attributable to the genus Pennatula. Both morphological and molecular (mtMutS, Cox1 and 28S genes) study of this material supports the polyphyletic nature of this genus and the need to resurrect the genus Ptilella Gray, 1870 to accommodate these and other species. A new species, Ptilella grayi n. sp., is described and illustrated. The species Pennatula bayeri is proposed to be a junior synonym of Pennatula bellissima (here also considered in the genus Ptilella)
Morpho-kinematic analysis of the point-symmetric, bipolar planetary nebulae Hb 5 and K 3-17, a pathway to poly-polarity
The kinematics of the bipolar planetary nebulae Hb~5 and K 3-17 are
investigated in detail by means of a comprehensive set of spatially resolved
high spectral resolution, long-slit spectra. Both objects share particularly
interesting characteristics, such as a complex filamentary, rosette-type
nucleus, axial point-symmetry and very fast bipolar outflows. The kinematic
information of Hb~5 is combined with {\it HST} imagery to construct a detailed
3D model of the nebula using the code SHAPE. The model shows that the large
scale lobes are growing in a non-homologous way. The filamentary loops in the
core are proven to actually be secondary lobes emerging from what appears to be
a randomly punctured, dense, gaseous core and the material that forms the point
symmetric structure flows within the lobes with a distinct kinematic pattern
and its interaction with the lobes has had a shaping effect on them. Hb~5 and
K~3-17 may represent a class of fast evolving planetary nebulae that will
develop poly-polar characteristics once the nebular core evolves and expands.Comment: 19 pages, 8 figures. To appear in The Astrophysical Journa
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