Catalog - Streptochilus cetacensis

CATALOG OF ORIGINAL DESCRIPTIONS: Streptochilus cetacensis Smart and Thomas (2007)

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.


Higher levels: pf_cat -> S -> Streptochilus -> Streptochilus cetacensis
Other pages this level: S. cetacensis, S. dubeyi, S. globiger infirmirugosus, S. inglei, S. latum, S. macdougallae, S. mascarenensis, S. pristinum, S. rockallkiddensis, S. subglobigerum, S. tasmanensis, S. tokelauae flexiserialis

Streptochilus cetacensis

Citation: Streptochilus cetacensis Smart and Thomas (2007)
Rank: Species
Type locality: SE Atlantic Ocean, ODP Site 1264;equatorial Atlantic Ocean, ODP Site 667.
Type age (chronostrat): Lower Miocene
Type specimens: The holotype (reg. no. BM(NH) PF 68062) is from ODP 208-1264B-21-1, 78-80cm, 210.60 mcd All other designated paratypes (reg. no. BM(NH) PF68063-68151, BM(NH) PF 68222-68251) and
Type repository: London, UK; NHM

Current identification/main database link: Streptochilus cetacense Smart and Thomas 2007


Original Description
Diagnosis. Test elongate, laterally slightly compressed, flared and typically ‘triangular’ in shape with curved and depressed sutures, with many specimens covered with evenly distributed pores.

Description. Test small to medium sized, elongate, increasing regularly in size, flared and typically ‘triangular’ in shape, laterally slightly compressed, periphery broadly rounded to somewhat lobulate, sometimes twisted, biserial; 5-8 pairs of chambers, slightly inflated, wider than high, increasing regularly in size as added; sutures curved and depressed; aperture high arch-shaped, offset slightly to one side of test, extending from the base of the last chamber onto apertural face, bordered by a thickened rim/collar along the top and outer side of the arch, the opposite side is turned inward to a plate connecting with the top of the collar and the inturned portion of the preceding foramen; wall smooth to finely granular, commonly affected by dissolution, finely perforate although mostly obscured by dissolution, chambers often show numerous, small pores evenly distributed over test, in some specimens enlarged by dissolution; no obvious differences between micro- and megalospheric specimens

Size: Dimensions. Specimens at the two sites (529 and 1264) on Walvis Ridge: length, 300-120μm (mean 188μm, St. Dev. 39, n = 249); thickness, 75-50μm (mean 62 μm, St. Dev. 6, n = 40).Specimens at Site 667: length,230-120μm (mean 157μm, St.Dev. 21, n = 105); maximum width, 120-80 μm (mean 91 μm,St. Dev. 10, n = 105); thickness, 65-45 μm (mean 55 μm, St.Dev. 6, n = 20).

Etymology: Named after the Latin for a large marine animal such as a whale, cetus, after the area where it has been found (Walvis Ridge [Walvis = Dutch for whale], SE Atlantic Ocean, ODP Sites 1264 and 1265 and DSDP Site 529.

Extra details from original publication
Remarks. Dissolution of tests commonly obscures detail; fine pores observable in later chambers unaffected by dissolution.Specimen size is variable with some specimens being relatively large, e.g., in sample  DSDP 74-529-8-3, 74-76cm (69.24 mbsf) the size of the specimens examined was: length, 300-130μm (mean 211μm, St. Dev. 38, n = 62); maximum width, 180-80μm (mean 131μm, St. Dev. 19, n = 62).

In contrast, specimens in sample DSDP 74-529-8-4, 72-74cm (70.72 mbsf) were consistently smaller: length, 260-130μm (mean 168μm, St. Dev. 29, n = 69); maximum width, 140-80μm (mean 107μm, St. Dev. 17, n = 69). Specimens from Site 667 (equatorial Atlantic Ocean) are overall smaller than those from the Walvis Ridge sites, and tend to have pores over all chambers of the test. Specimens from this location are included in S. cetacensis because they resemble the specimens from Walvis Ridge strongly,and the differences in size and pore distribution and size might be due to differential dissolution. Detailed morphological information from more locations is necessary in order to evaluate whether the equatorial group could be a different morphological species, or whether the variability is within the intra-group morphological variability of the species within the larger geographic region.
Streptochilus cetacensis  resembles Streptochilus sp. aff. S. martini (Pijpers) as illustrated in Poore and Gosnell(1985; Plate 1, figs. 8-16). Streptochilus cetacensis resembles Streptochilus globulosum (Cushman), but the latter is much more globose. Originally, the size of the holotype (Holotype USNM26172 in the Smithsonian Museum of Natural History,USA) was given as: length, 700μm; width, 400μm; thickness,150μm (Cushman 1933), which would have been much larger than our species, but these measurements were incorrect; the size of the holotype is length, 300μm and width, 130μm
(Cushman et al. 1954), as checked by E. Thomas.

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 mascarenensis closely resembles Streptochilus cetacensis, but Streptochilus mascarenensis is consistently more laterally compressed (thickness 50μm compared with 62μm), its periphery is more lobulate, and its pores are smaller.
Streptochilus cetacensis
is typically ‘triangular’ in shape and flared, and is clearly different from S.rockallkiddensis.Specimens of S.cetacensis at Site 667 are overall smaller than those from the southeastern Atlantic (Sites 529 and 1264) (text-fig. 3), and have distinctive pores over all chambers of the test.
The differences in pore distribution and size of S. cetacensis between the equatorial Atlantic specimens (Site 667) and southeastern Atlantic specimens might be due to differential dissolution.
Streptochilus cetacensis closely resembles S. mascarenensis, but S. cetacensis is consistently less laterally
compressed (thickness 62μm compared with 50μm), becomes thicker towards the apertural end, its periphery is less lobulate, and is more ‘triangular’ in shape. S. mascarenensis is clearly different from S. rockallkiddensis in its general shape, its more pronounced chambers, and absence of a coarsely roughened test.
For all three species, differentiating between microspheric and megalospheric specimens in non-sectioned specimens
is often unclear and speculative, although in sectioned/polished specimens it is possible to distinguish between
specimens that have relatively small (microspheric) or large (megalospheric) proloculi.

Editors' Notes
Orthography: Streptochilus is a neuter noun (Smart & Thomas 2018, p.501) so the correct form of the species name is cetacense, although it was given as cetacensis in the original description.

References:

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(1-2): 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 V O


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Streptochilus cetacensis compiled by the pforams@mikrotax project team viewed: 20-9-2021

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