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Joergensenium clevei
Dumitrica and Bjørklund, 2016
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Description - Add description
Joergensenium clevei Dumitrica and Bjørklund n. sp.
Text-figure 2.3; Plate 7
Description. Test as with the genus, consisting of 3 concentric shells of which one is cortical and two medullary. Cortical shell thin-walled, spherical with numerous polygonal (usually pentagonal or hexagonal) pores arranged irregularly and of relatively equal size (Pl. 7, Figs 1a, 2a). It is covered by numerous small by-spines originating not in the vertices of the pore frames but on the intervening bars of the frames (Pl. 7, Fig. 1). Sometimes, and on some portions, they can be interconnected by very thin bars. Microsphere has a shape of a short pentagonal prism with one lateral edge simple and straight or slightly curved, representing the MB, and the other four curved and provided with an additional radial bar (ad) in their middle. All corners represent points of origin of 10 rays, of which 2, at the ends of MB, are apical (A), 4 are basal (B), and the other 4 are antapical (ant), refer to Text-Fig. 2.3. At the level of the second medullary shell, all these rays are interconnected by arches forming a second prismatic shell with curved edges that repeats the fundamental shape of the microsphere. Second medullary shell has 7 cupolas erected on these edges (some cupolas are seen in Pl. 7, Figs 1b, 2c-e) and corresponding to the 7 facets of the polygonal prism. Cupolas are well marked especially in axial view, which is the view along the MB. All the 14 rays originate in the microsphere periphery in the arches of the second medullary shell, and only occasionally1-2 rays may be prolonged as thin rays up to the cortical shell. The tops of the 7 cupolas are at the origin of 7, three-bladed radial bars that traverse the cortical shell and extend outside it into pointed spines that usually are not longer than their inner portion.
Material. Two specimens observed in Cleve’s slide collection, located on Cleve slide #33.
Holotype. Pl. 7, Fig. 2. Stored at the Swedish Museum for Natural History with registration number SMNH Type-6120-1, England Finder coordinates J40/1.
Paratype. Pl. 7, Fig. 1. Stored at the Swedish Museum for Natural History with registration number SMNH Type-6120-2, England Finder coordinates G36/0.
Dimensions. Holotype: Diameter of microsphere 25 µm, of second medullary shell 46 µm, of cortical shell 101 µm. Paratype: Diameter of microsphere 27 µm, of second medullary shell 50 µm, of cortical shell 110 µm.
Etymology. The species is dedicated to the Swedish chemist, biologist, mineralogist, oceanographer Per Teodor Cleve (1840-1905) for his contribution to the knowledge of the radiolarians from the Spitzbergen area.
Range. So far this species has only been found in plankton material east of Spitzbergen (78° 18’N, 2° 58’W). An additional observation of J. clevei was made in DSDP Site 609, 2CC in the North Atlantic with an estimated age of about 313.000 years (Ciesielski and Bjørklund, 1995). The stratigraphic occurrence of this species was not looked for either below or above the 2CC sample. The stratigraphic significance of this species is therefore not known at present.
Remarks. Joergensenium clevei Dumitrica and Bjørklund n. sp. resembles J. arcticum Ikenoue, Dumitrica and Bjørklund n. sp., from which it differs in being much more regular, in having practically only 7 external spines, and in having the cortical shell normally one-shelled. It is possible that they are 2 contemporaneous species characterizing 2 geographical areas, the former the north Atlantic and the latter the north-western part of the Arctic Ocean with its main distribution and abundance in the Chukchi Sea. According to Cleve’s slide #33 the sampling was from 2000 m to the surface. In Cleve’s several slides, covering the sampling depth shallower than ca 400 m, no J. clevei was observed. Joergensenium rotatilis is observed in west Norwegian fjord plankton and is endemic to rather warm water (7° C). Joergensenium rotatilis is also found in surface sediment samples in the Norwegian Sea, but we have so far no information on which water mass it belongs to. As we have not observed J. clevei in our west Norwegian fjord fauna we assume this species might be a deep (> 400m) and cold water dweller, originating from the Arctic Ocean, and occupying the water masses underlying the warm Norwegian Sea Current (the continuation of the North Atlantic Current) in the area west of Spitzbergen. In conclusion, we may suggest the following: J. rotatile is a warm water boreal species with its home area in the Nordic Seas and the Norwegian fjords, J. clevei with a subarctic distribution in the northern part of the Norwegian Sea, and finally J. arcticum in the western part of the Arctic Ocean, probably endemic to the Chukchi Sea area, as it has not been registered elsewhere so far.
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