pforams@mikrotax - Streptochilus macdougallae pforams@mikrotax - Streptochilus macdougallae

Streptochilus macdougallae

Classification: pf_cenozoic -> Benthic origins -> Streptochilus -> Streptochilus macdougallae
Sister taxa: S. latum, S. subglobigerum, S. inglei, S. macdougallae ⟩⟨ S. cetacense, S. mascarenense, S. pristinum, S. rockallkiddense, S. tasmanense ⟩⟨ S. martini, S. sp.


Citation: Streptochilus macdougallae Miranda-Martínez, Carreño & McDougall 2017
taxonomic rank: Species

Catalog entries: Streptochilus macdougallae

Type images:

Distinguishing features:
Parent taxon (Streptochilus): Like Chiloguembelina but with an internal plate connecting successive chambers, a prominent extension of an apertural collar, and a smoother surface texture.
This taxon: 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.
They are being edited as the site is developed and comments on them are especially welcome.


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]

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]

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]

Character matrix
test outline:Subtriangularchamber arrangement:Biserialedge view:Compressedaperture:Interiomarginal
sp chamber shape:Subrectangularcoiling axis:N/Aperiphery:N/Aaperture border:Thin flange
umb chbr shape:Subrectangularumbilicus:N/Aperiph margin shape:Narrowly roundedaccessory apertures:None
spiral sutures:Moderately depressedumb depth:N/Awall texture:Reticulateshell porosity:Microperforate: <1µm
umbilical or test sutures:Moderately depressedfinal-whorl chambers:2-2 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

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.

Biostratigraphic distribution

Geological Range:
Last occurrence (top): within PL1 [Pac.] zone (4.37-5.6Ma, top in Zanclean stage). Data source: Miranda-Martínez et al. 2017
First occurrence (base): within M14 [Pac.] zone (5.6-6.14Ma, 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


Streptochilus macdougallae compiled by the pforams@mikrotax project team viewed: 10-12-2023

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