Marginulinopsis costata (Batsch 1791)
- Dataset
- Taxonomy of Middle Miocene foraminifera from the northern Namibian continental shelf
- Rank
- SPECIES
Classification
- kingdom
- Chromista
- phylum
- Foraminifera
- class
- Nodosariata
- order
- Vaginulinida
- family
- Vaginulinidae
- genus
- Marginulinopsis
- species
- Marginulinopsis costata
discussion
Remarks: The relative abundance of M. costata is generally low, forming trace components (<1 %) in some of the samples of core 2670. There is variation in the size of the tests. Smaller specimens measure up to 0.2 mm in cross section diameter and 1 mm in length, while some tests that are ornamented throughout, are large, measuring up to 0.4 mm in cross section and 2 mm in length. The tests show a variable degree of size and ornamentation. Similarly, there appears to be variation in the ornamentation within this species itself and among the synonymies. For example, the test in pl. 2, fig. 10 closely resembles the sketched imaged of Marginulina bifurcata in Fornasini (1902), with the terminal chamber being just as strongly costate as the preceding chambers. Marginulina bifurcata has, however, been synonymised into M. costata. The specimens in figures 11 and 12 resemble Marginulina raphanus (d’Orbigny, 1826), but that species has a pointed initial end, whereas specimens from this study area is rounded along the initial portion. There has also been confusion in the identification of this taxon. Barker (1960) re-identified this species as Marginulinopsis bradyi, whereas Jones (1994) split the figured identifications of M. costata in Brady (1884) into Vaginulinopsis bradyi and M. costata. The original specimen of Marginulina bradyi appears to be more initially coiled and flatter, broadening towards the terminal end, whereas M. costata does not show the same initial portion and later stages. In this study, the figured specimens have been identified as Marginulinopsis costata. The figured specimens 11 and 12 also resemble that of Marginulina sendaiensis in Asano (1937, 1949), possessing less or no ornamentation on their terminal chamber and are more abundant (up to 5 % in some of the samples) than those having tests completely covered in costae. The difference between Marginulina sendaiensis and M. costata is that the aperture of Marginulina sendaisensis is centrally located on the terminal chamber, but the aperture of M. costata is located excentrically. Life strategy: Species of this genus are generally shallow-infaunal in environments with variable conditions of low to high oxygen (Milker & Schmiedl, 2012). Global stratigraphic range: This species occurs from the Jurassic to Recent (Bagg, 1912). Regional occurrence: M. costata is documented to occur in middle Miocene sediments on the Namibian outer continental shelf, south of the Kunene River mouth (this study).