122,083 research outputs found
Cellaria spatulifera Achilleos & Gordon & Smith 2020, n. sp.
No full textCellaria spatulifera n. sp. (Fig. 7) Cellaria sp. 10: Achilleos et al. 2019: [4–7]. Material examined. Holotype: NIWA 128669, cruise TAN0413, Stn 109, 37.5488º S, 176.9878º E, Bay of Plenty, 136–142 m, collected 13 November 2004. Paratype: NIWA 128752, cruise TAN1105, Stn 43, 33.9875 º S, 171.7508 º E, Middlesex Bank, 170 m, 170–174 m, collected 28 March 2011. Etymology. Latin spatula, small spoon or paddle, plus fero, bear, carry, alluding to the shape of the avicularian mandible. Diagnosis. Colony branching laterally. Autozooids back to back in pairs, widening to whorls of three. Opesia wider than long with beaded distal rim and smooth convex proximal rim with knob-like condyles. Fully vicarious avicularia with spatulate rostrum and longitudinally oval foramen. Female zooids dimorphic, broader than autozooids, with semicircular ooecial opening. Description. Colony erect, jointed, laterally branched; stem fragments not> 10 mm in length. Stem slender, cylindrical in widest parts, narrower proximally and between ovicellate sections (W, 91–422 μm). Zooids arranged back to back in alternating pairs proximally, later whorls comprising 3 zooids; up to 16 whorls along a stem. Zooids unequally hexagonal in outline, longer than wide (ZL, 350–471 μm; ZW, 220–310 μm; ratio 1.43). Cryptocyst mostly smooth with sparse granulation except for opesial and proximal areas bounded by cryptocyst ridges; these ridges continuous proximally, almost merging with zooid margin distally. Opesia wider than long (OpL, 40–74 μm; OpW, 67–101 μm; ratio 0.7), its thin margin slightly raised, distally beaded, the strongly convex proximal rim flanked by upturned knob-like condyles. Avicularia fully vicarious; cystid more or less elongate-hexagonal but the distal third narrowest. Rostrum half the length of cystid; directed distally and slightly curved, spatulate overall, with triangular proximal third that broadens to spoon-shaped part which occupies full width of cystid distally. Palate smooth except for elongate hourglassshaped area with granulation distally, tuberculation proximally. Rostral foramen longitudinally oval. Mandibular pivots horizontal, their inner ends converging proximolaterally, not fusing but leaving thin suture. Avicularian opesia with widely narrow crescentic slit with granular proximal margin; cryptocyst inversely triangular, with sparse granulation. Edge of cryptocyst defined by smooth continuous ridges (AvCL, 402–449 μm; AvCW, 200–227 μm; ATL, 245–253 μm; ATW, 104–119 μm; RL, 233–236 μm; RW, 104–119 μm). Female zooids dimorphic, being broader than autozooids with wider opesiae. Ovicells with granular frontal face sloping downwards proximally to level below opesial rim; ooecial opening almost semicircular, with corners extended transversely as short slits (OvApL, 11–30 μm; OvApW, 30–84 μm; ratio 0.3). Ancestrula not definitely seen. Proximal-most zooids with frontal rootlet pores. Remarks. The avicularium of Cellaria spatulifera n. sp. is strikingly unique among the species in this genus. Overall, C. spatulifera n. sp. most resembles C. stenorhyncha n. sp. In fact, in the absence of avicularia the two species are easily confused, autozooids being more or less identical. Distribution. Endemic; Bay of Plenty, New Zealand, 136–142 m depth.Published as part of Achilleos, Katerina, Gordon, Dennis P. & Smith, Abigail M., 2020, Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region, pp. 201-236 in Zootaxa 4801 (2) on page 213, DOI: 10.11646/zootaxa.4801.2.1, http://zenodo.org/record/390035
Cellaria calculosa Achilleos & Gordon & Smith 2020, n. sp.
No full textCellaria calculosa n. sp. (Fig. 2) Cellaria sp. 6: Achilleos et al. 2019: [3–5, 7, 8]. Material examined. Holotype: NIWA 128673, cruise TAN0307, Stn 79, 49.8105º S, 175.3216º W, subantarctic slope, 887–908 m, collected 2 May 2003. Paratypes: NIWA 128672 cruise TAN0307, Stn 79, 49.8105º S, 175.3216º W, subantarctic slope, 887–908 m, collected 2 May 2003. Etymology. Latin, calx, pebbles, alluding to the pebbly surface of the zooids. Diagnosis. Colony branching dichotomously. Zooids in whorls of 3–4, their distal rims elevated. Opesia wider than long with beaded distal rim and convex proximal rim with upturned knob-like condyles. Interzooidal avicularia with triangular rostrum and narrow rounded tip; tiny transversely oval opesial foramen. Description. Colony erect, jointed, flexible, dichotomously branched; colony fragments not exceeding 15 mm in length. Stem sturdy, more or less cylindrical (W, 300–490 μm); slightly narrower close to node. Zooids somewhat elongate-hexagonal or rhomboidal in cystid outline, longer than wide (ZL, 328–492 μm; ZW, 236–336 μm; ratio 1.5), alternately, arranged in whorls of 3 zooids close to the nodes but increasing to 4 zooids per whorl in the middle part of the internode. Distal rims of zooids elevated, giving irregular profile to stems. Cryptocyst coarsely granular except in most depressed part proximal to opesia. Cryptocyst ridges continuous distally and more or less converging proximally. Opesia wider than long (OpL, 67–86 μm; OpW, 90–117 μm; ratio 0.7), set in the distal end occupying one-third of the total zooid length, beaded distally and smooth proximally; the proximal rim convex, flanked by upturned knob-like condyles. Avicularia common, interzooidal, smaller than the autozooid, situated distal or distolateral of parent zooid. Rostrum triangular with concave sides and narrowly rounded tip; directed distally or distolaterally. Mandibular pivots horizontal, stout, their inner ends bent distal, typically converging and forming an irregular ligula-like process. Rostral foramen more or less transversely oval; avicularian opesia tiny, oval or a small slit. Cryptocyst triangular extensive, granular. Mandibular areas granular; foramen with a smooth proximal margin (AvCL, 245–312 μm; AvCW, 192–193 μm; ATL, 153–188 μm; ATW, 111–123 μm; AopL, 47–57 μm; AopW, 50–53 μm; RL, 135–176 μm; RW, 111–123 μm). Ovicells not recorded. Ancestrula not clearly distinguished. Proximal-most zooids with opesia sometimes partially occluded; frontal surface with 7–8 conspicuous rootlet pores. Remarks. In the sum of its characters, Cellaria calculosa n. sp. resembles none of its congeners. The avicularium, in particular, while resembling in form the vicarious avicularia of a number of species, differs in being interzooidal. Only two other species have interzooidal avicularia of triangular form— Cellaria moniliorata Rogick, 1956 and Cellaria sagittula Hayward & Ryland, 1993 —but in both cases autozooids are whorled and the narrower avicularia have weakly developed or no mandibular pivots. Because the avicularia in C. calculosa n. sp. are not vicarious, it is germane to compare the species with taxa attributed to Paracellaria Moyano, 1969. Paracellaria elephantina Hayward & Thorpe, 1989 from the South Atlantic has similar autozooids but the avicularia are smaller and directed proximolaterally. Paracellaria elizabethae Branch & Hayward, 2005 from South Indian Ocean has similar avicularia, but the cryptocyst ridges are short and non-converging proximally (in contrast with C. calculosa n. sp., in which they converge). Distribution. Subantarctic slope east of Bollons Seamount, New Zealand, 887–908 m depth.Published as part of Achilleos, Katerina, Gordon, Dennis P. & Smith, Abigail M., 2020, Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region, pp. 201-236 in Zootaxa 4801 (2) on page 203, DOI: 10.11646/zootaxa.4801.2.1, http://zenodo.org/record/390035
Cellaria major Achilleos & Gordon & Smith 2020, n. sp.
No full textCellaria major n. sp. (Fig. 6) Cellaria sp. 11: Achilleos et al. 2019: [4–8]. Material examined. Holotype: NIWA 128676, Stn U 595, 30.3583° S, 173.1450° E, 1474 m, Three Kings Ridge NNE of Tui Seamount, collected 7 February 1988. Paratype: NIWA 144879, same data as holotype. Etymology. Latin major, greater, alluding to the large zooid size. Diagnosis. Colony branching not seen. Autozooids in whorls of 4–6. Opesia as wide as long, D-shaped with smooth rim; proximal rim with small condyles. Small interzooidal avicularia somewhat immersed, with semicircular rostrum, arched frontalwards; wide transversely narrow opesial foramen. Ooecia unknown. Description. Colony erect; three small internode fragments, each not> 4 mm in length. Stem large, more or less cylindrical (W, 0.924 –1.827 mm), with 4–6 zooidal chambers in cross section. Autozooids more or less elongate-hexagonal, longer than wide (ZL, 929–1320 μm; ZW, 618–808 μm; ratio 1.4). Cryptocyst concave, finely granular, highest at the zooidal margins with no cryptocystal ridges. Opesia almost as wide as long (OpL, 176–311 μm; OpW, 215–373 μm, ratio 0.8), more or less transversely D-shaped, with smooth little-raised edge, the proximal rim straight with small, mounded condyles. Space between opesia and distal zooid margin. Avicularia small, interzooidal, distal to parent zooid, somewhat immersed; cystid about the same size as autozooidal opesia, hemispherical or rounded-oblong, densely granular. Rostrum directed distally, semicircular, arched frontalwards, edge weakly scalloped; rostral foramen transversely elliptical. Mandibular pivots horizontal, converging, sometimes touching; if touching, the avicularian opesia separate, smaller than rostral foramen, transversely narrow; cryptocyst dipping inwards (downwards), mostly concealed by shelf edge of cystid (AvCL, 231–310 μm; AvCW, 332–374 μm; ATL, 149–114 μm; ATW, 78–92 μm; RL, 81–92 μm; RW, 78–92 μm). Ooecia not seen. Most autozooids have a small foramen distal to opesia that may be the locus of a future ooecium. Ancestrula not seen. Remarks. The zooids of C. major n. sp. are conspicuously large and can be seen with the naked eye. The interzooidal avicularium with semicircular rostrum somewhat resembles that in several other species, especially Cellaria australis MacGillivray, 1880 from Australia. The autozooids in C. australis, however, are more elongate and almost parallel-sided with a bean-shaped opesia (Bock 2019) and the cryptocyst is coarsely granular with straight cryptocystal ridges. Also, the proximal rim of the opesia in C. major n. sp. is straight instead of convex like in C. australis. European Cellaria fistulosa (Linnaeus, 1758), near-identical Cellaria parafistulosa d’Hondt & Gordon, 1999 from New Caledonia and Cellaria novanglia Winston & Hayward, 2012 from New England have similar inwarddipping avicularia, but these species have thinner mandibular pivots and autozooidal characters are significantly different (inter alia, a more fusiform shape and knob-like condyles). Distribution. Three Kings Ridge, 1474 m depth.Published as part of Achilleos, Katerina, Gordon, Dennis P. & Smith, Abigail M., 2020, Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region, pp. 201-236 in Zootaxa 4801 (2) on pages 211-213, DOI: 10.11646/zootaxa.4801.2.1, http://zenodo.org/record/390035
Jovian and Kronian Magnetodisc Field and Guiding Centre Dynamics of Trapped Particles Data
No full textData files and basic Matlab visualisation functionality of Jovian and Kronian UCL magnetodisc model output and guiding centre dynamics of trapped particles data described in the JGR Space Physics paper 2020JA027827 Trapped Particle Motion In Magnetodisk Fields by Guio, P. and Staniland, N. and Achilleos, N. A. and Arridge, C. S.(https://doi.org/10.1029/2020JA027827)</p
A multi-instrument view of tail reconnection at Saturn
No full textThree instances of tail reconnection events at Saturn involving the ejection of plasmoids downtail have been reported by Jackman et al. (2007) using data from Cassini’s magnetometer (MAG). Here we show two newly discovered events, as identified in the MAG data by northward/southward turnings and intensifications of the field. We discuss these events along with the original three, with the added benefit of plasma and energetic particle data. The northward/southward turnings of the field elucidate the position of the spacecraft relative to the reconnection point and passing plasmoids, while the variability of the azimuthal and radial field components during these events indicates corresponding changes in the angular momentum of the magnetotail plasma following reconnection. Other observable effects include a reversal in flow direction of energetic particles, and the apparent evacuation of the plasma sheet following the passage of plasmoids
Structure of the interplanetary magnetic field during the interval spanning the first Cassini fly-through of Saturn's magnetosphere and its implications for Saturn's magnetospheric dynamics
No full textWe examine the interplanetary magnetic field (IMF) data obtained by the Cassini spacecraft during a 5 month period spanning the first fly-through of Saturn's magnetosphere, this interval corresponding to six solar rotations at the spacecraft. It is shown that the structure of the interplanetary medium was consistent with expectations for the declining phase of the solar cycle, generally consisting of two IMF sectors and two corotating interaction region compressions during each solar rotation. Field strengths and consequent estimated reconnection voltages at Saturn's magnetopause were overall weaker by a factor of about two compared with those observed during the immediately preceding interval investigated by Jackman et al. (J. Geophys. Res., 109, A11203, doi:10.1029/2004JA010614, 2004). Specifically, during the four solar rotations immediately preceding the fly-through, it is estimated that the total open flux produced at Saturn's magnetopause was ∼60 GWb per solar rotation, compared with ∼100 GWb per solar rotation estimated similarly for the earlier interval. These values compare with estimates of ∼35 GWb of open magnetic flux typically present in Saturn's tail lobes and polar cap. However, in the solar rotation immediately following the fly-through, it is found that field and voltage values recovered to former overall values.</p
FIGURE 8. Cellaria stenoryncha n in Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region
No full textFIGURE 8. Cellaria stenoryncha n. sp., TAN0413/109. A. Branch bifurcation with broader ovicellate internodes. B. Operculate autozooids and ovicellate zooids. C. Vicarious avicularium with mandible. Scale bars: A, 500 μm; B, 150 μm; C, 100 μm.Published as part of Achilleos, Katerina, Gordon, Dennis P. & Smith, Abigail M., 2020, Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region, pp. 201-236 in Zootaxa 4801 (2) on page 215, DOI: 10.11646/zootaxa.4801.2.1, http://zenodo.org/record/390035
FIGURE 6. Cellaria major n in Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region
No full textFIGURE 6. Cellaria major n. sp., NIWA Stn U595. A. Autozooids and avicularium. B. Close up of part of (A). C. Opesia with blunt condyles. D. Close up of an avicularium. Scale bars: A, 500 μm; B, 250 μm; C, D 150 μm.Published as part of Achilleos, Katerina, Gordon, Dennis P. & Smith, Abigail M., 2020, Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region, pp. 201-236 in Zootaxa 4801 (2) on page 212, DOI: 10.11646/zootaxa.4801.2.1, http://zenodo.org/record/390035
FIGURE 2. Cellaria calculosa n in Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region
No full textFIGURE 2. Cellaria calculosa n. sp., TAN307/79. A. Internode with autozooids and avicularia. B. Opesia with condyles. C. Interzooidal avicularium. D. Distal tip of internode with rootlet pores and avicularium. E. Proximal end of internode with paired avicularia and autozooids with well-developed rootlet pores. Scale bars: A, D, 500 μm; B, C, 100 μm; E, 300 μm.Published as part of Achilleos, Katerina, Gordon, Dennis P. & Smith, Abigail M., 2020, Cellaria (Bryozoa, Cheilostomata) from the deep: new species from the southern Zealandian region, pp. 201-236 in Zootaxa 4801 (2) on page 205, DOI: 10.11646/zootaxa.4801.2.1, http://zenodo.org/record/390035
Mapping Saturn's Nightside Plasma Sheet Using Cassini's Proximal Orbits
No full textBetween April and the end of its mission on 15 September, Cassini executed a series of 22 very similar 6.5‐day‐period proximal orbits, covering the mid‐latitude region of the nightside magnetosphere. These passes provided us with the opportunity to examine the variability of the nightside plasma sheet within this time scale for the first time. We use Cassini particle and magnetic field data to quantify the magnetospheric dynamics along these orbits, as reflected in the variability of certain relevant plasma parameters, including the energetic ion pressure and partial (hot) plasma beta. We use the University College London/Achilleos‐Guio‐Arridge magnetodisk model to map these quantities to the conjugate magnetospheric equator, thus providing an equivalent equatorial radial profile for these parameters. By quantifying the variation in the plasma parameters, we further identify the different states of the nightside ring current (quiescent and disturbed) in order to confirm and add to the context previously established by analogous studies based on long‐term, near‐equatorial measurements
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