Notes on the benthic foraminiferal genus Heteromorphina R.W. Jones, and Heteromorphina amplivestibulata sp. nov

Oolina heteromorpha Parr, 1950, the type species of the genus Heteromorphina R.W. Jones, 1984 is demonstrated to be a junior synonym of Lagena collaris Cushman, 1913. In addition, two of the three species transferred by Jones to this genus are shown to belong to other genera. From the Miocene of DSDP Site 357 (Leg 39), located on the Rio Grande Rise, a new species, Heteromorphina amplivestibulata, is described and illustrated. It is characterized by an extremely large chamberlet in comparison to the principal chamber, which has a slightly produced caudal structure with a hollow central canal.


INTRODUCTION
The study of unilocular foraminifera has received increased attention in recent years. One of the major papers in this regard was that of R.W. Jones (1984), revising the classification of unilocular foraminifera. Among several new genera proposed was Heteromorphina R.W. Jones, type species Oolina heteromorpha Parr, 1950. In the course of the present author's study of Recent benthic foraminifera from the southwest Pacific Ocean and the relevant literature necessary to identify that material, it became apparent that there were systematic problems concerning taxa assigned to this genus. The type species was a junior synonym of a species erected by Cushman (1913), other species reassigned to the new genus by Jones did not belong there, and Patterson (1986) Cushman, 1913, p.10. Description. Test ovoid to teardrop shaped, unilocular, principal chamber surmounted by apertural chamberlet, the two separated by depressed horizontal suture. Wall smooth. Aperture terminal, round, furnished with entosolenian tubes, one into chamberlet, some specimens may have a second entosolenian tube in main chamber. Remarks. Jones (1984) erected this genus with Oolina heteromorpha Parr, 1950 as the type species, and also reassigned two previously described species to the genus. In addition, two species were illustrated but not named. All five forms were represented in his material by single specimens, illustrated by single scanning electron microscope (SEM) views, with no accompanying description or remarks.
While studying material from the southwest Pacific Ocean, the present author encountered specimens of this genus, and found one of them described and illustrated in Cushman's (1913) monograph of the Lagenidae of the North Pacific Ocean. The specimen is in all respects identical with both Lagena collaris Cushman (1913, p.10, pI.1, fig.2), and the specimen assigned by Jones (1984, p1.1, fig.2) to H . heteromorpha Pam, the type species. Reference to Pam's (1950, p.304, p1.8, fig.6) type description and figures of Oolina heteromorpha indicates the two species are synonymous. Applying the rule of priority, Cushman's species becomes the type, and Pam's a junior synonym. The type figures of both these species are reproduced herein as Fig.lA and Fig.lB respectively. Cushman's type description reads in part "aperture nearly circular, opening into a separate cavity which connects with the larger part of the test by a short entosolenian tube" (Cushman, 1913, p.lO), and there is no question of its "bilocular" nature. On the other hand, Parr described an "apertural end tapering gently and ending in a rounded mass of clear shell material which surrounds the aperture", and also remarked on "the neck being replaced by a rounded bead of clear shell material" (Parr, 1950, p.304). It is possible that there is no chamberlet in Parr's species, but in all likelihood he was simply unable to recognize the upper clear area as being a distinct hollow chamberlet.
The other two species transferred to Heteromorphina by Jones (1984) are most likely not referable to this genus. Loeblich and Tappan remarked that "Nodosaria calomorpha Reuss, 1 866, placedhere byR.W. Jones( 1984, *1615), isprobablyajuvenile Dentalina" (Loeblich and Tappan, 1987, p.427). In fact Jones transferred only one specimen illustrated by Reuss (1866, p. 129, pl. 1, fig. 15, not figs. 16-19) and part of the description to Heteromorphina, probably on the basis of the entosolenian tube figured therein. Nevertheless, the upper chamber is at least the equal of the lower and as strongly inflated, the suture is very strongly depressed, and the whole bears very little resemblance to the present genus. The species should be retained in the genus Nodosaria Lamarck, 1812, or possibly placed in the genus Laevidentalina Loeblich and Tappan, 1986 if curvature of the test is judged sufficient. The particular figured specimen remains problematical, however, due to the apparent entosolenian tube, a feature not found in either of these latter two genera.
As to the second of these two species, Lagena apiculata (Reuss) var. punctulata Sidebottom,19 12 clearly lacks a chamberlet, as is shown particularly in Sidebottom's (1912) plate 14, figure 23, but also in his plate 14, figures 21 and 22, in which there is no trace of a suture or interruption in the pattern of coarse perforations. The specimen illustrated in Fig.2 of the present paper is from Scripps Institution of Oceanography core LSDH 78V, interval 0-4cm, 4"30 S Lat. and 167"58'E Long.
The lack of a chamberlet is readily apparent as is the asymmetry of the test outline, and it clearly belongs in Oolina d'Orbigny, 1839 and not Heteromorphina.
Derivation of name. From the Latin, amplus, large, + vestibulum, entrance court or vestibule, with reference to the chamberlet as compared to the main chamber, + ata, provided with. Diagnosis. A species of Heteromorphina with an ellipsoidal main chamber, produced base with caudal depression, and large tapering chamberlet which is over one-third the total test length. Types and occurrences. All specimens are from the Miocene section of DSDP Site 357 (Leg 39), located at 30"00.25' S Lat. and 35O33.5 1'W Long. on the Rio Grande Rise in the southwest Atlantic Ocean. Figured holotype GSC 9605 1 is from Core 4, Section 5,80-86cm, figured paratype GSC 96052 is from Core 10, Section 1,84-90cm, and unfigured paratype GSC 96053 is from Core 7, Section 1,80-86cm. All specimens are deposited in the collection of the Geological Survey of Canada, Ottawa. Description. Test unilocular, surmounted by apertural chamberlet, principal chamber ellipsoidal in outline and circular in section, at least one-and-a-half times as long as broad, with greatest diameter at its middle, base slightly produced or tapered, with heavy rim surrounding small caudal depression. Chamberlet elongate, one-and-a-half times as long as broad and Oolina punctulata (Sidebottom), SIO core LSDH 78V. over one-third of total test length, circular in section, tapering steadily toward aperture from greatest breadth at base, which is some two-thirds of chamber diameter, joined to chamber along a horizontal depressed suture. Wall smooth. Aperture terminal, round, piercing slightly thickened hyaline rim, with free straight entosolenian tube of about one-half chamberlet length, presence or absence of entosolenian tube in principal chamber indeterminate due to opaque state of preservation of specimens. Dimensions. Length of figured holotype GSC 9605 1 0.466mm. diameter 0.172mrn; length of figured paratype GSC 96052 0.288mm, diameter 0.1 1Omm. Remarks.This species is readily distinguishedfrom H . collaris by the proportionately much larger chamberlet of the present species, as well as its ellipsoida! main chamber with greatest breadth near the middle. Because the three specimens are remarkably consistent in character, and are from three stratigraphically distinct samples, this author has not hesitated to erect this new species.