Emendation of Riveroinella martinezpicoi Bermúdez and Seiglie, 1967, and Synonymy of Riveroinella with Cassigerinella Pokorný, 1955

Abstract

The monotypic genus Riveroinella was erected by Bermudez and Seiglie in 1967 as belonging to the family Ceratobuliminidae, a group of benthonic foraminifera characteristically having an aragonitic shell. Examination of its type species, R. martinezpicoi, reveals that the genus Riveroinella is a junior synonym of the planktonic foraminiferal genus Cassigerinella Pokorny, 1955, not only because R. martinezpicoi has an enrolled biserial coil in the last whorl, but also because the shell of R. martinezpicoi is calcitic, not aragonitic as claimed in the original description. A detailed morphologic examination of the type species of the genus Cassigerinella, C. chipolensis (Cushman and Ponton), was made with the use of a scanning electron microscope (SEM), because some authors have assigned this species to the benthonic foraminiferal family Cassidulinidae in the belief that C. chipolensis has an internal tooth plate. Our SEM examination indicates that Cassigerinella possesses no tooth plate, but instead a distinct rimlike protruding apertural flange. Therefore, the genus is herein retained in the planktonic foraminiferal family Hantkeninidae. INTRODUCTION Bermudez and Seiglie (1967) erected the monotypic foraminiferal genus Riveroinella, with type species Riveroinella martinezpicoi, placing it in the family Ceratobuliminidae because they believed its shell to be made of aragonite. While studying the foraminifera from JOIDES Hole 3 on the Blake Plateau off northern Florida (Bunce et al., 1965), the senior author observed an apparently new species of Cassigerinella, associated with Globigerinoides sicanus de Stefani, Globorotalia peripheroronda Banner and Blow, and Praeorbulina glomerosa (Blow). In describing planktonic foraminifera recovered during DSDP (Deep Sea Drilling Project) Leg 34 from the eastern Pacific Ocean, Quilty (1 976, p. 651, pl. 19, figs. 13-14) figured a Cassigerinella closely resembling the Cassigerinella specimen that the senior author recognized from the Blake Plateau. In general morphology, both of these specimens of Cassigerinella are closely comparable with Riveroinella martinezpicoi Bermudez and Seiglie, and the question was posed as to whether R. martinezpicoi is indeed an independent genus characterized by a planispiral test and an aragonitic shell, as was originally contended by Bermudez and Seiglie (1967). Examination of the holotype (USNM 687203) and two paratypes (687204, 687205), on loan from the United States National Mseum of Natural History in Washington, D. C., indicates that the specimen from the Blake Plateau is taxonomically identical with the type specimens of R. martinezpicoi and that chambers in the last whorl of R. martinezpicoi are arranged in an enrolled biserial coil in the manner characteristic of the genus Cassigerinella (text-figure 1). The purpose of this paper is to demonstrate that Riveroinella is a junior synonym of Cassigerinella, not only because its type species has an enrolled biserial coil in the last whorl, but also because the shell of R. martinezpicoi is calcitic, not aragonitic as claimed in the original description given by BermOdez and Seiglie in 1967. SYSTEMATIC PALEONTOLOGY Superfamily GLOBIGERINACEA Carpenter, Parker and Jones, 1862 Family HANTKENINIDAE, Cushman, 1927 Subfamily CASSIGERINELLINAE Bolli, Loeblich and Tappan, 1957 Genus Cassigerinella Pokorny, 1955 Discussion: In the original description, Pokorny (1955) suggested merely that the genus Cassigerinella is closely related to the genus Globigerinella. Bolli, Loeblich and Tappan (1957) were the first to assign Cassigerinella to the superfamily Globigerinacea, which includes only taxa having a planktonic mode of life. This assignment has been micropaleontology, vol. 23, no. 3, pp. 319-329, pls. 1-2, july, 1977 319 This content downloaded from 207.46.13.51 on Tue, 21 Jun 2016 06:55:29 UTC All use subject to http://about.jstor.org/terms