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Current identification/main database link: Streptochilus rockallkiddense Smart and Thomas 2007
Diagnosis. Test small, elongate, laterally slightly compressed, biserial becoming staggered uniserial, commonly rectilinear and often narrower towards apertural end, aperture with thickened rim and often obscured, surface ornamentation varying from smooth to granular.
Description. Test small, elongate, laterally slightly compressed,periphery rounded and non-lobulate, shape variable, commonly elongate, parallel-sided and rectilinear, occasionally flared, in some elongate specimens the later formed part of the test may narrow towards the apertural end, biserial tending to staggered uniserial in some elongate specimens, rarely twisted; most specimens have 6 pairs of chambers but the number of pairs varies from 5-8 or more, chambers increase regularly in size as added, slightly wider than high, initial chambers small and often obscured by granular surface ornamentation; sutures slightly curved and depressed; final chamber often has thickened rim; aperture
low-arch shaped, offset to one side of test, with an internal plate formed by the infolding and downward extension of one margin of the rimmed aperture, often small and obscured by thickening; wall uniformly very finely perforate,surface ornamentation varies from smooth to finely granular to coarsely granular and, where present, ornamentation constitutes half or more of the test occurring from proloculus towards apertural end; no obvious differences between micro- and megalospheric specimens.
Size: Dimensions. Length, 260-130μm (mean 187μm, St. Dev. 28, n =115); maximum width, 100-70μm (mean 84 μm, St. Dev. 6, n =115); thickness, 70-60μm (mean 63 μm, St. Dev. 4, n = 20).
Extra details from original publication
Remarks. The granular surface texture displayed by a high proportion of specimens can be difficult to discern under a light microscope, but becomes clear when specimens are viewed under a SEM. The degree of roughness of the test varies from specimen to specimen and from sample to sample. In the specimens examined from Site 608, the percentage of roughened specimens varies from ~68% (sample DSDP 608-37X-4, 38-40cm, n = 110) to ~37% (sample DSDP 608-37X-6,38-40cm, n = 115). Specimens from DSDP Sites 400 and 563 often have a roughened appearance. Typically the roughened appearance makes up half of the test, although in some specimens this may be one-third, two-thirds, three-quarters or more of the test.
The number of parallel-sided and flared tests varies between specimens and between samples, although parallel-sided
individuals are generally more common. The roughened appearance obscures the chambers, although these are discernible when specimen is wetted.
Streptochilus rockallkiddensis closely resembles Bolivina sp. 9 of Poag and Low (1985, pl. 1, figs 16,17, 18) reported from DSDP Site 548. Their illustrations clearly show the variability of test roughness ranging from smooth (pl. 1, fig.16), to one-third roughened (pl. 1, fig. 17) to three-quarters roughened (pl. 1, fig. 18).
Thomas (1986, 1987) referred to Streptochilus rockallkiddensis as Bolivina spathulata (Williamson).
A specimen from Site 563 has been illustrated in Smart and Murray (1994, Fig.Fig. 2, 1) and Smart and Ramsay (1995, Fig. 2).
Early Miocene Streptochilus spp. occurred coevally at various sites in the Atlantic and Indian Oceans, but the species differ morphologically from site to site. Streptochilus rockallkiddensis is the most variable species and differs from all other species in its typically parallel-sided/rectilinear shape which often narrows towards the apertural end, the tendency to become staggered uniserial, and thickening of the wall including the rim of the aperture which may obscure the aperture. The variability of surface ornamentation is a feature of this species which varies from smooth to granular, the granular nature constituting typically half or more of the test occurring from proloculus to apertural end.
Orthography: Streptochilus is a neuter noun (Smart & Thomas 2018, p.501) so the correct form of the species name is rockallkiddense, although it was given as rockallkiddensis in the original description.
Smart, C. W. & Thomas, E. (2007). Emendation of the genus Streptochilus Brönnimann and Resig 1971 (Foraminifera) and new species from the lower Miocene of the Atlantic and Indian Oceans. Micropaleontology. 53(01-Feb): 73-103, 103 figures, 113 lates, 101 table. gs Smart, C. W. & Thomas, E. (2018). Taxonomy, biostratigraphy, and phylogeny of Oligocene Streptochilus. In, Wade, B. S. , Olsson, R. K. , Pearson, P. N. , Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 46(Chap 19): 495-511. gs
Smart, C. W. & Thomas, E. (2007). Emendation of the genus Streptochilus Brönnimann and Resig 1971 (Foraminifera) and new species from the lower Miocene of the Atlantic and Indian Oceans. Micropaleontology. 53(01-Feb): 73-103, 103 figures, 113 lates, 101 table. gs
Smart, C. W. & Thomas, E. (2018). Taxonomy, biostratigraphy, and phylogeny of Oligocene Streptochilus. In, Wade, B. S. , Olsson, R. K. , Pearson, P. N. , Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 46(Chap 19): 495-511. gs
Streptochilus rockallkiddensis compiled by the pforams@mikrotax project team viewed: 5-12-2019
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