Catalog entries: Streptochilus macdougallaeType images:
Distinguishing features: Wall cancellate sometimes with coarse pores; test laterally compressed last two chambers slightly sub-inflated. Sutures oblique.NB These concise distinguishing features statements are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus.
Wall type: Wall exhibits a cancellate texture and mural-like pores, sometimes with coarse pores. In some specimens, early middle portion of the test shows coarse interpore and anastomosing ridges displaying a rough texture (Pl. IV, fig. 5b); sometimes the roughness is extended with no clear pattern to the latest former chambers, which otherwise exhibit a low relief honeycomb-like surface (Pl. IV, fig. 2c), and a rugose texture at the top of the latest chambers (Pl. IV, fig. 2b). [Miranda-Martínez et al. 2017]
Test morphology: Biserial, small to medium size test. Elongate and triangular shape in frontal view. Laterally compressed. Periphery slightly lobulate. 5 to 7 pairs of subrectangular chambers, which increase moderately as added. The last two chambers are larger, slightly semi-inflated and slightly overlapping. Faint lobes at the base of the chamber could be in contact with the suture. Sutures obscured by the ornamentation in the early portion, otherwise incised, curved, oblique from the midline and arched gently upward towards the periphery beneath the chambers lobes (Pl. IV, fig. 2a).
Aperture consists of a moderately wide elongate arch located perpendicular to the middle plane of the test, from the base of the last chamber onto apertural face, bordered by a thick rim/collar with a thick and wide internal plate formed by the infolding and downward extension of one margin of the rimmed aperture (Pl. IV, fig. 11). [Miranda-Martínez et al. 2017]
Size: Dimensions. Length 133–312 μm (mean 225 μm, n = 27); max- imum width 86–149 μm (mean 117 μm, n = 13); minimum width 15–27 μm (mean 20 μm, n = 13), maximum thickness 41–87 μm (64 μm, n = 19); minimum thickness 16–40 μm (mean 25 μm, n = 19). [Miranda-Martínez et al. 2017]
|test outline:||Subtriangular||chamber arrangement:||Biserial||edge view:||Compressed||aperture:||Interiomarginal|
|sp chamber shape:||Subrectangular||coiling axis:||N/A||periphery:||N/A||aperture border:||Thin flange|
|umb chbr shape:||Subrectangular||umbilicus:||N/A||periph margin shape:||Narrowly rounded||accessory apertures:||None|
|spiral sutures:||Moderately depressed||umb depth:||N/A||wall texture:||Reticulate||shell porosity:||Microperforate: <1µm|
|umbilical or test sutures:||Moderately depressed||final-whorl chambers:||2.0-2.0||N.B. These characters are used for advanced search. N/A - not applicable|
Similar species: The general outline of Streptochilus macdougallae sp. nov. is quite similar to morphotype B of S. globigerus (Schwager) identified in the Gulf (Pl. II, 3a), but differs in being laterally compressed; with the last two formed chambers slightly sub-inflated, instead of globose, with chamber slightly overlapping and exhibiting some faint lobes in the base, and distinctive sutures.
Last occurrence (top): within PL1 [Pac.] zone (4.37-5.60Ma, top in Zanclean stage). Data source: Miranda-Martínez et al. 2017
First occurrence (base): within M14 [Pac.] zone (5.60-6.14Ma, base in Messinian stage). Data source: Miranda-Martínez et al. 2017
Plot of occurrence data:
Primary source for this page: Miranda-Martínez et al. 2017
McDougall, K. & Miranda-Martinez, A. (2014). Evidence for a marine incursion along the lower Colorado River corridor. Geosphere. 10: 842-869. gs :: :: Miranda-Martinez, A. Y., Carreño, A. L. & McDougall, K. (2017). The Neogene genus Streptochilus (Brönnimann and Resig, 1971) from the Gulf of California. Marine Micropaleontology. 132: 35-52. gs :: ::
McDougall, K. & Miranda-Martinez, A. (2014). Evidence for a marine incursion along the lower Colorado River corridor. Geosphere. 10: 842-869. gs :: ::
Miranda-Martinez, A. Y., Carreño, A. L. & McDougall, K. (2017). The Neogene genus Streptochilus (Brönnimann and Resig, 1971) from the Gulf of California. Marine Micropaleontology. 132: 35-52. gs :: ::
Streptochilus macdougallae compiled by the pforams@mikrotax project team viewed: 4-6-2020
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