SYSTEMATIC PALEONTOLOGY

A full systematic treatment with synonymies for all diatom taxa identified in the present study is not given here. Individual species are annotated with the original author name and short references to accessible and quality illustrations. A few brief notes are also given on unusual varieties, problematic taxa, and stratigraphic distributions. Several specimens are illustrated in Plates P1, P2, and P3. Our taxonomy is based primarily on descriptions and illustrations of taxa from Neogene sections in Antarctic and Subantarctic waters. The following reports form the basis of this pool of literature: Abbott (1974), McCollum (1975), Gombos (1977), Schrader (1976), Fenner et al. (1976), Akiba (1982), Ciesielski (1983, 1986), Gersonde and Burckle (1990), Gersonde (1991), Fenner (1991), Baldauf and Barron (1991), Harwood and Maruyama (1992), Mahood and Barron (1996a, 1996b), Gersonde and Bárcena (1998), Bohaty et al. (1998), Zielinski and Gersonde (2002), and Censarek and Gersonde (2002). Several reports from North Pacific cores and outcrops also provide taxonomic guidelines for Miocene diatom taxa, including Barron (1985a), Akiba (1986), Akiba and Yanagisawa (1986), Yanagisawa and Akiba (1990), Akiba et al. (1993), Yanagisawa (1995), Gladenkov and Barron (1995), and Komura (1998).

The goal of the current investigation is to identify important marker datums and delineate zonal boundaries. Some taxonomic problems, however, arose in the identification of several taxa. Along with the common problem of taxonomic variability within and between samples, the presence of intermediate or transitional forms complicated the precise placement of datum levels. Intermediate forms, for example, were noted between Thalassiosira jacksonii and T. inura, Fragilariopsis aurica and F. barronii, Fragilariopsis praeinterfrigidaria and F. interfrigidaria, F. interfrigidaria and F. weaveri, and F. barronii and F. kerguelensis. In the F. barronii lineage, however, there is a transition over a narrow stratigraphic interval from intermediate F. aurica-F. barronii forms to F. barronii. Stricter taxonomic divisions than those currently defined are needed to further refine the Southern Ocean zonal scheme. Ideally, the zonal boundaries are those defined by the first or last common appearance of "sensu stricto" forms.

A number of Neogene diatom taxa have recently been transferred from the genus Nitzschia to Fragilariopsis (Gersonde and Bárcena, 1998; Zielinski and Gersonde, 2002; Censarek and Gersonde, 2002). We have followed these revisions, with a few exceptions. Nitzschia miocenia and N. reinholdii, for example, are currently left assigned to Nitzschia, pending further SEM investigation of these taxa.

Actinocyclus actinochilus (Ehrenberg) Simonsen, 1982, pp. 101-116, pl. 1-4; Villareal and Fryxell, 1983, p. 461, figs. 21-32.

Actinocyclus curvatulus Janisch in Schmidt; Koizumi, 1973, p. 831, pl. 1, figs. 1-6; Akiba, 1982, pp. 41, 42, pl. 5, figs. 5a-6.

Actinocyclus dimorphus (Castracane) Harwood and Maruyama, 1992, p. 700, pl. 12, fig. 16(?); pl. 13, figs. 3-5; pl. 17, figs. 19, 20 (Pl. P1, fig. 11).

Actinocyclus fasciculatus Harwood and Maruyama, 1992, p. 700, pl. 13, figs. 14, 15; Censarek and Gersonde, 2002, p. 350, pl. 1, fig. 5.

Actinocyclus ingens Rattray; Akiba, 1982, p. 42, pl. 5, figs. 7-14; Gersonde, 1990, pp. 791, 792, pl. 1, figs. 1, 3-5; pl. 3, figs. 8, 9; pl. 4, fig. 1.

Actinocyclus ingens var. nodus Baldauf in Baldauf and Barron, 1980, p. 104, pl. 1, figs. 5-9; Gersonde, 1990, p. 792, pl. 1, fig. 6; pl. 3, figs. 4-7; Censarek and Gersonde, 2002, p. 350, pl. 1, fig. 4.

Actinocyclus ingens var. ovalis Gersonde, 1990, p. 792, pl. 1, fig. 7; pl. 3, figs. 1-3; pl. 5, figs. 4, 7; pl. 6, figs. 1, 4-5; Censarek and Gersonde, 2002, p. 350, pl. 1, figs. 6, 8 (Pl. P1, figs. 2, 3).

Remarks: Harwood and Maruyama (1992) transferred A. ingens var. ovalis to the genus Hemidiscus and elevated the variety "ovalis" to species status. We retain the original designation, however, because of its close affinity with A. ingens. In addition, Hemidiscus ovalis Lohman (1938, pp. 91, 92, pl. 22, fig. 9) maintains priority over H. ovalis Harwood and Maruyama (1992). Specimens identified in the present study as A. ingens var. ovalis are restricted to morphologies with a strongly oval to broadly rounded lanceolate valve outline (see Pl. P1, figs. 2, 3). A. ingens var. ovalis is oval shaped and symmetrical in valve outline and possesses reduced areolation in the central area; these features distinguish it from Hemidiscus karstenii.

Actinocyclus ingens var. 1 (Pl. P1, figs. 7, 12).

Description and remarks: This precursor form to A. ingens is characterized by closely packed areolae and light silicification of the central area. In Hole 1138A, A. ingens var. 1 has a lowest occurrence in Sample 183-1138A-23R-CC (210.85 mbsf), just below the FO of A. ingens s.s.

Actinocyclus ingens var. 2 (Pl. P1, figs. 8, 9).

Description and remarks: A. ingens var. 2 is a distinctive form of A. ingens with a small valve diameter (25 µm) and a hyaline central area. It is distinguished from A. ingens var. A of Harwood and Maruyama (1992, p. 700, pl. 12, figs. 4, 5) by its small valve diameter. This form was only observed in Pleistocene Sample 183-1138A-4R-1, 25-26 cm, and, therefore, may have a restricted range.

Actinocyclus karstenii Van Heurck; Harwood and Maruyama, 1992, p. 700, pl. 13, figs. 1, 2, 6-8, 10, 11, 13; Mahood and Barron, 1996b, p. 288, pl. 3, fig. 5; Zielinski and Gersonde, 2002, p. 253, pl. 3, figs. 4, 5, 7-9, 12(?).

Actinocyclus maccollumii Harwood and Maruyama, 1992, p. 700, pl. 17, fig. 29.

Actinoptychus senarius (Ehrenberg) Ehrenberg; Akiba, 1986, pl. 29, fig. 2.

Araniscus lewisianus (Greville) Komura, 1998, pp. 6-8, figs. 20-22, 87-104, and text fig. 1.

Basionym: Coscinodiscus lewisianus Greville; Schrader, 1973, p. 703, pl. 8, figs. 1-6, 10, 15; Schrader, 1976, p. 631, pl. 14, fig. 3; Harwood and Maruyama, 1992, p. 702, pl. 6, fig. 13.

Asterolampra tela Gombos and Ciesielski, 1983, p. 600 as Asterolampra sp. A, but in pl. 3, figs. 1-4 as Asterolampra tela.

Asteromphalus hookeri Ehrenberg; Akiba, 1982, p. 42, pl. 1, fig. 1; Bohaty et al., 1998, pl. 2, fig. 5.

Asteromphalus kennettii Gersonde, 1990, p. 793, pl. 2, fig. 1; pl. 6, fig. 2; Harwood and Maruyama, 1992, p. 701, pl. 11, fig. 3; Censarek and Gersonde, 2002, p. 350, pl. 1, fig. 2.

Asteromphalus oligocenicus Schrader and Fenner, 1976, pp. 965, 966, pl. 21, figs. 8, 13, 14; pl. 28, fig. 1.

Asteromphalus parvulus Karsten; Fenner et al., 1976; p. 769, pl. 4, figs. 20, 21.

Note: A. parvulus and A. hookeri were grouped together in the present study (Table T1).

Asteromphalus symmetricus Schrader and Fenner, 1976, p. 966, pl. 21, figs. 7, 10-12.

Azpeitia gombosi Harwood and Maruyama, 1992, p. 701, pl. 3, figs. 1, 2.

Azpeitia harwoodii Bohaty and Shiono n. sp. (Pl. P1, fig. 10; Pl. P3, figs. 1-6, 10-13).

Synonym: Azpeitia sp. B of Shiono, 2000a (doctoral thesis), pl. 34, figs. 1-6; pl. 35, figs. 1-6.

Description: Valve is heavily silicified and circular in outline. Valve diameter ranges from 18 to 60 µm. Valve face is flat with no central depression. Areolae are roughly equal in size across valve face, with four to six areolae in 10 µm. The arrangement of the areolae on the valve face varies from to sublineate to subeccentric, and the packing of areolae in the central area ranges from very dense to moderately dense. The valve possesses a steep mantle with an areolate margin. A thin mantle ridge is present between the valve face and mantle on some specimens, but this feature is commonly absent. Two to three areolae are present on the mantle between the valve face and valve edge. A central labiate process is positioned slightly off center, with a small, round external opening that lacks an external tube structure. Six to ten marginal, equally spaced labiate processes are also present with small, round external openings near the valve face-mantle transition. Both central and marginal labiate processes open internally to a flared tube structure. Some specimens display a weakly developed central hyaline ring on the exterior of the valve and/or increased silicification between the central areolae.

Type Level and Locality: Sample 183-1138A-11R-6, 100-101 cm, ODP Hole 1138A, Central Kerguelen Plateau.

Holotype: Pl. P3, fig. 1 (high and low focus).

Type Specimen: Slide deposited in the California Academy of Science microfossil slide collection, CAS Slide Number 221034, CAS Accession Number 619994. Specimen is mounted in Norland optical adhesive and marked with a double scribe circle on cover slip.

Stratigraphic Distribution: A. harwoodii is documented in Pliocene sections from both the Southern Ocean and North Pacific. In the present study, A. harwoodii was observed in lower Pliocene sediments of ODP Hole 1138A, where it is common in all examined samples from Core 183-1138A-11R. The stratigraphic range for A. harwoodii in Hole 1138A (corresponding to Core 183-1138A-11R), falls within Subchron C2Ar, with an estimated age range of ~4.2 to 3.7 Ma. In the Hole 1138A section, however, the FO of A. harwoodii lies just above an unconformity and its lower range may therefore be truncated. A. harwoodii has also been observed in lower Pliocene samples from ODP Hole 1165B (Bohaty and Whitehead, unpubl. data), located on the Antarctic continental rise (to the south of Site 1138).

In the northwest Pacific, A. harwoodii is recorded in Pliocene samples from DSDP Hole 579A. In this section, rare specimens of A. harwoodii were observed in middle Pliocene Samples 86-579A-11-2, 30-31 cm, and 11-5, 30-31 cm, and in lower Pleistocene Samples 4-3, 12-13 cm, and 5-5, 25-26 cm. The Pliocene interval of Hole 579A is assigned an age of ~3.6 to 3.4 Ma, which is a slightly younger occurrence than documented at Southern Ocean Site 1138. The Pleistocene occurrence of A. harwoodii in Hole 579A may be due to reworking, based on the rarity of specimens.

Remarks: A pseudonodulus on the valve margin of A. harwoodii was not identified in SEM examination of specimens from Hole 1138A. A pseudonodulus, however, was noted on some specimens from Hole 579A (Shino, 2000b, pl. 34, fig. 4). Pending further SEM work on this taxon, we have elected not to include the presence of a pseudonodulus as part of the description of A. harwoodii.

A. harwoodii belongs to the "Azpeitia nodulifera group" described by Shiono and Koizumi (2002). Taxa within this group are characterized by the absence of a marginal hyaline area. A. harwoodii is taxonomically similar to Azpeitia nodulifera (see Fryxell et al., 1986, p. 19, 20, figs. XVII, XVIII-1, 2, 4, 5, and XXX-3, 4), a modern species found in warm-water regions (Hasle and Syvertsen, 1996). A. harwoodii, however, is typically smaller in diameter (18-55 µm) than A. nodulifera (20-100 µm). Additionally, A. harwoodii is more heavily silicified than A. nodulifera and lacks a well-developed mantle ridge.

A form similar to A. harwoodii was described by Shiono and Koizumi (2002) as "Azpeitia sp. A." In contrast to A. harwoodii, Azpeitia sp. A is characterized by a slight central depression and radial arrangement of valve-face areolae.

Paleoecology: Given the warm-water affinity of modern taxa in the "Azpeitia nodulifera group" (Hasle and Syvertsen, 1996; Shiono and Koizumi, 2002), the presence of A. harwoodii at Sites 579, 1138, and 1165 may be associated with local Pliocene warming at these sites in the North Pacific and Southern Oceans.

Derivation of Name: This species is named in honor of Dr. David Harwood at the University of Nebraska-Lincoln for his contributions to the development of Southern Ocean diatom biostratigraphy.

Authorship: The description of this new taxon is co-authored by Dr. Masamichi Shiono at Hokkaido University, Sapporo, Japan.

Azpeitia tabularis (Grunow) Fryxell and Sims in Fryxell et al., 1986, pp. 16-18, figs. XIV, XV, XXX-I; Censarek and Gersonde, 2002, p. 350, pl. 1, fig. 7.

Bogorovia gombosii (Desikachary) Yanagisawa, 1995, pp. 27-29, figs. 4-1, 4-2, 5-1, 5-2.

Bogorovia veniamini Jousé ex Yanagisawa, 1995, pp. 29-31, figs. 4-3 through 4-10, 8-1 through 8-10.

Cavitatus jouseanus (Sheshukova) Williams; Akiba et al., 1993, pp. 20-22, figs. 6-19, 6-20; Censarek and Gersonde, 2002, p. 350, pl. 5, fig. 12.

Cavitatus miocenicus (Schrader) Akiba and Yanagisawa in Akiba et al., 1993, p. 28, figs. 9-1 through 9-11.

Cavitatus rectus Akiba and Hiramatsu in Akiba et al., 1993, pp. 28-30, figs. 6-7 through 6-15.

Cestodiscus pulchellus Greville; Harwood and Maruyama, 1992, p. 701, pl. 3, figs. 6, 7.

Chaetoceros bulbosum (Ehrenberg) Heiden; Akiba, 1982, p. 42, pl. 7, fig. 9; Bohaty et al., 1998, pl. 5, fig. 12.

Chaetoceros lorenzianus Grunow; Harwood et al., 2000, fig. 7-q.

Chaetoceros sp. A of Harwood and Maruyama, 1992, p. 701, pl. 19, figs. 5-7.

Corethron criophilum Castracane; Krebs, 1983, p. 285, pl. 2, fig. 4a, b; Harwood and Maruyama, 1992, p. 701, pl. 19, figs. 8-11; pl. 5, fig. 15.

"Coscinodiscus" rhombicus Castracane; Barron, 1985b, p. 782, figs. 9.11, 9.12; Ciesielski, 1986, pl. 5, fig. 12; Harwood and Maruyama, 1992, p. 702, pl. 3, figs. 16, 17; pl. 8, figs. 12, 13; pl. 11, fig. 1; Censarek and Gersonde, 2002, p. 350, pl. 1, fig. 3.

Remarks: This taxon may be better placed in the genus Araniscus Komura 1998.

Coscinodiscus marginatus Ehrenberg; Schrader, 1973, p. 703, pl. 20, figs. 7, 10, 12, 13; Schrader, 1976, p. 631, pl. 12, fig. 2.

Crucidenticula ikebei Akiba and Yanagisawa, 1986, pp. 485, 486, pl. 1, figs. 1, 2; Yanagisawa and Akiba, 1990, pp. 228, 229, pl. 1, figs. 10-12; pl. 8, figs. 8-13.

Remarks: Specimens identified here as C. ikebei in Hole 1138A are similar to forms illustrated as Crucidenticula kanayae by Harwood and Maruyama (1992, pl. 7, fig. 15). The specimens identified in Hole 1138A are grouped as C. ikebei, rather than Crucidenticula sawamurae, because they possess slightly tapered apices.

Crucidenticula nicobarica Akiba and Yanagisawa, 1986, pp. 486, 487, pl. 1, fig. 9; pl. 2, figs. 1-7; pl. 5, figs. 1-9; Yanagisawa and Akiba, 1990, p. 232, pl. 1, figs. 23-29; Censarek and Gersonde, 2002, p. 351, pl. 2, figs. 25, 26.

Dactyliosolen antarcticus Castracane; Hasle, 1975, pp. 119-121, figs. 90-100, 109-112; Harwood and Maruyama, 1992, p. 702, pl. 18, fig. 12.

Comments: Only the wedge-shaped, girdle-band ends of D. antarcticus are commonly found in sediment samples.

"Denticula" sp. cf. Denticula norwegica Schrader in Schrader and Fenner, 1976, p. 978, pl. 1, fig. 38; Akiba and Yanagisawa, 1986, p. 487, pl. 2, figs. 15-21; pl. 6, figs. 1-9.

Denticulopsis crassa Yanagisawa and Akiba, 1990, pp. 248, 249, pl. 3, figs. 21-27; pl. 12, figs. 1-8; Censarek and Gersonde, 2002, p. 351, pl. 2, fig. 12.

Denticulopsis dimorpha var. areolata Yanagisawa and Akiba, 1990, p. 257, pl. 4, figs. 40, 41, 50-54; pl. 5, figs. 13-17; pl. 6, figs. 1-5, 15-23; pl. 12, figs. 15, 16.

Denticulopsis dimorpha Schrader (Simonsen) var. dimorpha Yanagisawa and Akiba, 1990, pp. 254, 255, pl. 4, figs. 42-49; pl. 7, figs. 14-16.

Denticulopsis "hustedtii var. aspera" Maruyama in Harwood and Maruyama, 1992, p. 702, pl. 10, figs. 8-11, 15, 16.

Remarks: Because of taxonomic revisions in the Denticulopsis group by Yanagisawa and Akiba (1990), this form should be renamed, or the variety name "aspera" should be elevated to species status.

Denticulopsis hyalina (Schrader) Simonsen; Yanagisawa and Akiba, 1990, pp. 240, 241, pl. 2, figs. 14, 33, 34; pl. 9, figs. 8, 9.

Denticulopsis maccollumii Simonsen; Yanagisawa and Akiba, 1990, pp. 264, 265, pl. 2, figs. 39-41; Harwood and Maruyama, 1992, p. 702, pl. 6, fig. 22; pl. 7, fig. 17; pl. 9, fig. 27; Censarek and Gersonde, 2002, p. 351, pl. 2, figs. 32-34.

Denticulopsis ovata (Schrader) Yanagisawa and Akiba, 1990, pp. 257, 258, pl. 6, figs. 6-14, 24-32; Censarek and Gersonde, 2002, p. 351, pl. 2, figs. 13-20.

Synonym: Denticulopsis meridionalis Harwood and Maruyama, 1992, pp. 702, 703, pl. 6, figs. 1-4; pl. 7, figs. 1-4, 6-9, 11-13; pl. 9, figs. 1-4, 10-14; pl. 10, fig. 7.

Denticulopsis praedimorpha Barron ex Akiba var. praedimorpha Yanagisawa and Akiba, 1990, pp. 251, 252, pl. 4, figs. 3-5, 10, 12-17, 39; pl. 5, figs. 4-12; Censarek and Gersonde, 2002, p. 351, pl. 2, figs. 1-7.

Denticulopsis simonsenii Yanagisawa and Akiba, 1990, pp. 242, 243, pl. 3, figs. 1-3; pl. 11, figs. 1, 5; Censarek and Gersonde, 2002, p. 351, pl. 2, figs. 21-24.

Remarks: D. simonsenii was separated from Denticulopsis vulgaris following the taxonomy of Yanagisawa and Akiba (1990). D. vulgaris is characterized by reduced punctation on the valve face, with striae positioned near each pseudoseptum, whereas D. simonsenii is characterized by full punctation between the psuedospeta. However, some intermediate forms were observed, and poorly preserved specimens in some intervals were difficult place into either group.

Denticulopsis vulgaris (Okuno) Yanagisawa and Akiba, 1990, pp. 243, 244, pl. 3, figs. 4-8; pl. 11, figs. 2, 6-10.

Remarks: See notes under Denticulopsis simonsenii.

Entopyla spp. (Pl. P2, fig. 19).

Remarks: A distinctive specimen belonging to the genus Entopyla was noted in Sample 183-1138A-8R-5, 100-101 cm (see Pl. P2, fig. 19).

Eucampia antarctica (Castracane) Mangin; Krebs, 1983, p. 285, pl. 3, figs. 3a, b; Mahood and Barron, 1996b, p. 290, pl. 1, figs. 1-3; pl. 7, figs. 1, 2.

Eucampia antarctica var. "twista"

Remarks: This variety of E. antarctica has not been formally described and is characterized by rotation (up to 90°) on the valvar plane, similar to the Paleogene species Hemiaulus rectus var. twista Fenner.

Fragilariopsis arcula (Gersonde) Gersonde and Bárcena, 1998, p. 92; Censarek and Gersonde, 2002, p. 351, pl. 3, figs. 15-18.

Basionym: Nitzschia arcula Gersonde, 1991, pp. 143, 144, pl. 2, fig. 4; pl. 4, fig. 4; pl. 5, figs. 1-6.

Fragilariopsis aurica (Gersonde) Gersonde and Bárcena, 1998, p. 92; Censarek and Gersonde, 2002, p. 351, pl. 3, figs. 9-12; Zielinski and Gersonde, 2002, p. 257, pl. 1, figs. 13-15.

Basionym: Nitzschia aurica Gersonde, 1991, pp. 144-146, pl. 1, figs. 18-25; pl. 3, fig. 5; pl. 4, figs. 5, 6; pl. 7, fig. 6.

Fragilariopsis barronii (Gersonde) Gersonde and Bárcena, 1998, p. 92; Zielinski and Gersonde, 2002, p. 257, pl. 1, figs. 29-31.

Basionym: Nitzschia barronii Gersonde, 1991, pp. 146, 147, pl. 3, fig. 6; pl. 4, figs. 1-3; pl. 5, figs. 7-17.

Remarks: Intermediate forms between F. barronii and F. aurica were noted near the FO of F. barronii. These intermediate forms were recorded separately as Fragilariopsis sp. cf. F. barronii.

Fragilariopsis clementia (Gombos) Zielinski and Gersonde, 2002, p. 33; Censarek and Gersonde, 2002, p. 351, pl. 3, figs. 7, 8.

Basionym: Nitzschia clementia Gombos, 1977, p. 595, pl. 8, figs. 18, 19; Gersonde and Burckle, 1990, p. 779, pl. 2, figs. 22, 23 (Pl. P2, figs. 8, 9).

Fragilariopsis curta (Van Heurck) Hustedt; Hasle, 1965, pp. 32, 33, pl. 6, fig. 6; pl. 12, figs. 2-5; pl. 13, figs. 1-6; pl. 16, fig. 6; pl. 17, fig. 5.

Basionym: Fragilaria curta Van Heurck, 1909, p. 24, pl. 3, fig. 37.

Synonym: Nitzschia curta (Van Heurck) Hasle, 1972, p. 115; Krebs, 1983, p. 286, pl. 4, fig. 4; Hasle and Medlin, 1990, p. 181, pl. 24.6, figs. 2-5.

Fragilariopsis cylindrus (Grunow) Krieger in Helmcke and Krieger; Hasle, 1965, pp. 34-37, pl. 12, figs. 6-12; pl. 14, figs. 1-10; pl. 17, figs. 2-4.

Synonym: Nitzschia cylindrus (Grunow) Hasle, 1972, p. 115; Hasle and Medlin, 1990, p. 181, pl. 24.6, figs. 6-11.

Fragilariopsis donahuensis (Schrader) Censarek and Gersonde, 2002, p. 350, pl. 3, figs. 13, 14.

Basionym: Nitzschia donahuensis Schrader, 1976, p. 633, pl. 2, fig. 30; Gersonde and Burckle, 1990, p. 780, pl. 1, figs. 16-18.

Fragilariopsis efferans (Schrader) Censarek and Gersonde, 2002, p. 350.

Basionym: Nitzschia efferans Schrader, 1976, p. 633, pl. 2, figs. 1, 3, 5-7.

Fragilariopsis fossilis (Frenguelli) Medlin and Sims, 1993, pp. 332, 333; Censarek and Gersonde, 2002, p. 351, pl. 3, figs. 3, 4; Zielinski and Gersonde, 2002, p. 257, pl. 1, figs. 5, 6.

Synonym: Nitzschia fossilis (Frenguelli) Kanaya in Kanaya and Koizumi; Schrader, 1973, p. 707, pl. 4, figs. 9-11, 24, 25; Gersonde and Burckle, 1990, p. 780, pl. 1, figs. 19, 20.

Fragilariopsis heardensis Bohaty n. sp. (Pl. P2, figs. 1-7; Pl. P3, fig. 9).

Description: Valve is clavate in outline and heteropolar. Ends are broadly rounded in shape, with one inflated end and one narrow, tapered end. There are 9 to 14 transapical striae in 10 µm across the valve face. Striae are straight, except at the terminal margin of the inflated end, where they are curved. Valve is lightly silicified, and small areolae that form uniseriate striae are faintly visible in the light microscope when mounted in a high-index medium. The valve is 35 to 85 µm in length and 10 to 12 µm wide at its widest point. Raphe is positioned on the margin.

Comments: This form is morphologically similar to Fragilariopsis clementia (see Gombos, 1977, pl. 8, figs. 18, 19; Gersonde and Burckle, 1990, pl. 2, figs. 22, 23) and Fragilariopsis lacrima (see Gersonde, 1991, pl. 1, figs. 1-6, 26; pl. 2, figs. 1-3). F. heardensis, however, is characterized by a more inflated, claviform shape than these two taxa. Additionally, N. clementia possesses more prominent costae when viewed in the light microscope and F. lacrima possesses coarser areolation. F. heardensis, F. clementia, and F. lacrima are compared in Plate P2; illustrated specimens of F. lacrima possess finer areolation than is typical of the taxon (Pl. P2, figs. 10, 11). Other taxa, such as Nitzchia efferens Schrader and Nitzschia claviceps Schrader show similarities to F. heardensis but also are coarser in their areolar structure. F. heardensis is also separated stratigraphically from these older Miocene taxa.

A range of F. heardensis morphologies was recognized in Hole 1138A, with differences in the coarseness of transapical striae, valve length, and the shape of the valve ends (highly rounded to broadly rounded). We have attempted to illustrate variation within this group, and the "end-members" are best represented by figures 1 and 3 on Plate P2.

Type Level and Locality: Sample 183-1138A-8R-5, 100-101 cm, ODP Hole 1138A, Central Kerguelen Plateau.

Holotype: Pl. P2, fig. 1a (differential interference contrast) and Pl. P2, fig. 1b (phase contrast).

Type Specimen: Slide deposited in the California Academy of Science microfossil slide collection, CAS Slide Number 221033, CAS Accession Number 619993. Specimen is mounted in Naphrax and is marked with a scribe circle on the coverslip.

Stratigraphic Distribution: F. heardensis was observed over a narrow stratigraphic interval (74.04-69.80 mbsf) in the upper Pliocene of Hole 1138A (Table T1). It is commonly fragmented as a result of its lightly silicified valve construction and is rare in all samples examined from Hole 1138A. F. heardensis was also observed in the upper Pliocene section of Hole 745B (S. Bohaty, unpubl. data), located on the Southern Kerguelen Plateau. Although also rare in Hole 745B, this taxon was noted in Samples 119-745B-13H-2, 10 cm; 13H-2, 42 cm; and 13H-3, 68 cm (111.10-113.18 mbsf). All three of these samples contain Thalassiosira insigna and Thalassiosira vulnifica, placing its range in a narrow interval within the T. insigna-T. vulnifica Zone in both Holes 745B and 1138A.

Derivation of Name: This taxon is named in reference to Heard Island, located 180 km northwest of Site 1138.

Fragilariopsis interfrigidaria (McCollum) Gersonde and Bárcena, 1998, p. 92; Zielinski and Gersonde, 2002, p. 259, pl. 1, figs. 20, 21.

Basionym: Nitzschia interfrigidaria McCollum, 1975, p. 535, pl. 9, figs. 7-9; Ciesielski, 1983, p. 655, pl. 1, figs. 11-18; Gersonde and Burckle, 1990, p. 780, pl. 1, figs. 1-3 (Pl. P2, figs. 15-18).

Remarks: Large forms of F. interfrigidaria (see Pl. P2, figs. 17, 18) were noted above the LO of Fragilariopsis weaveri within the Thalassiosira insigna-Thalassiosira vulnifica and Thalassiosira vulnifica Zones (71.30-66.80 mbsf). Although these specimens are included here as F. interfrigidaria, they may be taxonomically distinct from lower to middle Pliocene forms (see Pl. P2, figs. 15, 16). See also notes under Fragilariopsis praeinterfrigidaria.

Fragilariopsis januaria (Schrader) Bohaty n. comb.

Basionym: Nitzschia januaria Schrader, 1976, p. 634, pl. 2, figs. 25-29.

Remarks: Following the taxonomic revisions of Gersonde and Bárcena (1998), Zielinski and Gersonde (2002), and Censarek and Gersonde (2002), this taxon is transferred to the genus Fragilariopsis.

Fragilariopsis kerguelensis (O'Meara) Hustedt; Hasle, 1965, pp. 14-18, pl. 3, figs. 4, 5; pl. 4, figs. 11-18; pl. 5, figs. 1-11; pl. 6, figs. 2-4; pl. 7, fig. 9; pl. 8, fig. 10; pl. 16, figs. 3-5.

Synonym: Nitzschia kerguelensis (O'Meara) Hasle, 1972, p. 115; Fenner et al., 1976, p. 776, pl. 2, figs. 19-30; Hasle and Medlin, 1990, p. 181, pl. 24.2, figs. 11-18 (Pl. P2, fig. 13).

Remarks: F. barronii grades into F. kerguelensis in the upper part of its range (see illustrations of transitional forms in Zielinski and Gersonde, 2002, pl. 1, figs. 25-28). Identification of these two taxa is uncertain in the uppermost Pliocene-lower Pleistocene interval of Hole 1138A. Also, "early" forms of F. kerguelensis (see Pl. P2, fig. 13) possess smaller areolae than typical modern forms of F. kerguelensis.

Fragilariopsis lacrima (Gersonde) Gersonde and Bárcena, 1998, p. 92; Censarek and Gersonde, 2002, p. 351, pl. 3, figs. 5, 6; Zielinski and Gersonde, 2002, p. 259, pl. 1, figs. 8, 9.

Basionym: Nitzschia lacrima Gersonde, 1991, p. 148, pl. 1, figs. 1-6, 26; pl. 2, figs. 1-3 (Pl. P2, figs. 10, 11).

Fragilariopsis matuyamae Gersonde and Bárcena, 1998, p. 93, pl. 1, figs. 1-9, 13-16; pl. 2, figs. 1, 4, 5, 7-9; Zielinski and Gersonde, 2002, p. 259, pl. 1, figs. 10, 11.

Fragilariopsis obliquecostata (Van Heurck) Heiden in Heiden and Kolbe; Hasle, 1965, pp. 18-20, pl. 7, figs. 2-7.

Synonym: Nitzschia obliquecostata (Van Heurck) Hasle, 1972, p. 115; Fenner et al., 1976, pp. 776, 777, pl. 2, figs. 15-18.

Fragilariopsis praecurta (Gersonde) Gersonde and Bárcena, 1998, p. 92; Censarek and Gersonde, 2002, pp. 351, 352, pl. 3, figs. 19-21.

Basionym: Nitzschia praecurta Gersonde, 1991, pp. 148, 149, pl. 1, figs. 7-17; pl. 2, figs. 5, 6; pl. 3, figs. 3, 4; pl. 10, fig. 7.

Fragilariopsis praeinterfrigidaria (McCollum) Gersonde and Bárcena, 1998, p. 92; Zielinski and Gersonde, 2002, p. 259, pl. 1, figs. 22, 23; Censarek and Gersonde, 2002, p. 352, pl. 3, figs. 22, 23.

Basionym: Nitzschia praeinterfrigidaria McCollum, 1975, p. 535, pl. 10, fig. 1; Ciesielski, 1983, p. 655, pl. 2, figs. 1-8, 13-16; pl. 3, fig. 5.

Remarks: As noted above, intermediate forms between F. praeinterfrigidaria and F. interfrigidaria were noted in the Pliocene section of Hole 1138A. These forms possessed light silicification between the transapical costae.

Fragilariopsis pusilla (Schrader) Censarek and Gersonde, 2002, p. 350, pl. 3, fig. 25.

Basionym: Nitzschia pusilla Schrader, 1976, p. 634, pl. 2, fig. 20.

Fragilariopsis pseudonana (Hasle) Hasle; Hasle, 1965, pp. 22-24, pl. 1, figs. 7-14; pl. 4, figs. 20, 21; pl. 8, figs. 1-9; pl. 17, fig. 6.

Basionym: Nitzschia pseudonana Hasle, 1974, p. 427; Fenner et al., 1976, p. 777, pl. 2, figs. 6-11; Hasle and Medlin, 1990, p. 181, pl. 24.1, figs. 7-14.

Remarks: See Hasle and Syvertsen (1996) for comments on the taxonomy of this species.

Fragilariopsis rhombica (O'Meara) Hustedt; Hasle, 1965, pp. 24-26, pl. 1, fig. 6; pl. 4, fig. 19; pl. 6, fig. 5; pl. 8, fig. 11; pl. 9, figs. 1-6; pl. 10, figs. 2-6.

Synonym: Nitzschia angulata Hasle, 1972, p. 115; Fenner et al., 1976, p. 775, pl. 1, figs. 17-39; Hasle and Medlin, 1990, p. 181, pl. 24.1, fig. 6; pl. 24.2, fig. 19; pl. 24.4, figs. 1-6.

Fragilariopsis ritscheri Hustedt; Hasle, 1965, pp. 20, 21, pl. 1, fig. 20; pl. 3, fig. 3; pl. 4, figs. 1-10; pl. 5, figs. 12, 13; pl. 6, fig. 1; pl. 7, fig. 8.

Synonym: Nitzschia ritscheri (Hustedt) Hasle, 1972, p. 115; Fenner et al., 1976, p. 777, pl. 3, figs. 1-12; Hasle and Medlin, 1990, p. 181, pl. 24.1, fig. 20; pl. 24.2, figs. 1-10; pl. 24.3, fig. 9.

Fragilariopsis separanda Hustedt; Hasle, 1965, pp. 26, 27, pl. 9, figs. 7-10; pl. 10, fig. 1; Zielinski and Gersonde, 2002, p. 259, pl. 1, figs. 16, 17.

Synonym: Nitzschia separanda (Hustedt) Hasle, 1972, p. 115; Fenner et al., 1976, p. 777, pl. 1, figs. 1-16; Hasle and Medlin, 1990, p. 181, pl. 24.2, figs. 7-10.

Fragilariopsis weaveri (Ciesielski) Gersonde and Bárcena, 1998, p. 93; Zielinski and Gersonde, 2002, p. 260, pl. 1, figs. 18, 19.

Basionym: Nitzschia weaveri Ciesielski, 1983, p. 655, pl. 1, figs. 1-10.

Hemidiscus sp. cf. H. cuneiformis Wallich; Schrader, 1973, p. 706, pl. 24, fig. 14; Fenner et al., 1976, p. 774, pl. 11, fig. 17; Harwood and Maruyama, 1992, p. 703, pl. 11, fig. 11; Censarek and Gersonde, 2002, p. 352, pl. 4, fig. 5.

Hemidiscus karstenii Jousé; Abbott, 1974, p. 313, pl. 1, figs. D-F; Fenner, 1991, p. 108, pl. 1, fig. 2; Censarek and Gersonde, 2002, p. 352, pl. 3, fig. 27.

Hemidiscus karstenii f. 1 of Ciesielski, 1983, p. 656, pl. 4, figs. 2-5, but not pl. 4, fig. 1.

Remarks: This form is described with widely spaced areolae in the central area (Ciesielski, 1983). We strictly apply this definition and exclude specimens with closely packed areolae in the central area (Ciesielski, 1983, pl. 4, fig. 1). In contrast, Zielinski and Gersonde (2002, p. 260) apply "H. karstenii f. 1" to specimens with closely packed areolae in the central area.

Hemidiscus triangularus (Jousé) Harwood and Maruyama, 1992, p. 703; Censarek and Gersonde, 2002, p. 352, pl. 4, figs. 1-4.

Basionym: Cosmiodiscus insignis f. triangula Jousé; Ciesielski, 1983, p. 656, pl. 5, figs. 1-10; Ciesielski, 1986, p. 876, pl. 4, figs. 5, 6.

Hemiaulus incisus Hajós; Gombos and Ciesielski, 1983, pl. 20, fig. 6.

Hyalodiscus radiatus (O'Meara) Grunow in Cleve and Grunow; Harwood et al., 2000, p. 459, fig. 8g.

Ikebea sp. B of Scherer et al., 2000, p. 434, pl. 1, figs. 22, 23.

Lithodesmium minisculum Grunow in Van Heurck; Schrader, 1973, p. 706, pl. 12, figs. 7(?), 15, 17.

Navicula directa (Smith) Ralfs in Pritchard; Krebs, 1983, p. 285, pl. 3, fig. 7.

Neobrunia mirabilis (Brun in Brun and Tempère) Kuntze; Hendy, 1981, p. 11, pl. 1, figs. 1-3; pl. 2, figs. 4-7; pl. 3, figs. 10-13.

Synonym: Brunia mirabilis (Brun in Brun and Tempère) Tempère; Ciesielski, 1983, p. 655, pl. 7, figs. 1, 2.

Nitzschia denticuloides Schrader, 1976, p. 633, pl. 3, figs. 7, 8, 10, 12, 18-24; pl. 15, fig. 22; Harwood and Maruyama, 1992, p. 704, pl. 8, figs. 5-8, 17; pl. 9, figs. 24-26; pl. 10, fig. 1; Censarek and Gersonde, 2002, p. 352, pl. 2, figs. 27-31.

Nitzschia grossepunctata Schrader, 1976, pp. 633, 634, pl. 3, figs. 1-4; Harwood and Maruyama, 1992, p. 704, pl. 10, fig. 2; Censarek and Gersonde, 2002, p. 352, pl. 2, figs. 37, 38.

Nitzschia maleinterpretaria Schrader, 1976, p. 634, pl. 2, figs. 9, 11-19, 21, 24.

Synonym: Fragilariopsis maleinterpretaria (Schrader) Censarek and Gersonde, 2002, p. 351, pl. 3, fig. 26.

Nitzschia miocenica Burckle; Ciesielski, 1983, p. 656, pl. 2, figs. 9-12; Akiba, 1986, p. 443, pl. 23, figs. 10, 14; Akiba and Yanagisawa, 1986, p. 496, pl. 39, figs. 7-15; pl. 41, figs. 1, 2.

Synonym: Fragilariopsis miocenica (Burckle) Censarek and Gersonde, 2002, p. 351.

Remarks: N. miocenica is consistently present in upper Miocene samples of Hole 1138A (Table T1).

Nitzschia panduriformis Gregory; Abbott, 1974, p. 316, pl. 11, fig. A.

Nitzschia reinholdii Kanaya ex Schrader, 1973, p. 708, pl. 4, figs. 12-16; pl. 5, figs. 1-9; Akiba, 1986, pp. 443, 444, pl. 22, figs. 4, 5; Akiba and Yanagisawa, 1986, p. 496, pl. 40, figs. 8, 9; pl. 41, figs. 3, 4.

Synonym: Fragilariopsis reinholdii (Kanaya) Zielinski and Gersonde, 2002, p. 259, pl. 1, figs. 3, 4; Censarek and Gersonde, 2002, p. 352, pl. 3, figs. 1, 2.

Nitzschia sp. 17 of Schrader, 1976, p. 634, pl. 3, figs. 13-15, 17; pl. 2, fig. 10.

Paralia sulcata (Ehrenberg) Cleve.

Synonym: Melosira sulcata (Ehrenberg) Kützing; Schrader, 1973, p. 706, pl. 20, fig. 9.

Porosira pseudodenticulata (Hustedt) Jousé in Kozlova; Krebs, 1983, p. 286, pl. 4, fig. 13.

Radialiplicata clavigera (Grunow) Gleser; Scherer et al., 2000, p. 436, pl. 6, fig. 7.

Raphidodiscus marylandicus Christian; Andrews, 1978, p. 400, pl. 5, figs. 23, 24; Schrader, 1976, p. 635, pl. 5, fig. 19; pl. 15, fig. 16.

Rhabdonema japonicum Tempère and Brun; Scherer et al., 2000, p. 436, pl. 5, fig. 10.

Rhizosolenia costata Gersonde, 1991, pp. 149, 150, pl. 9, figs. 1-6; pl. 10, figs. 1-6; Harwood and Maruyama, 1992, p. 705, pl. 18, figs. 1, 2.

Rhizosolenia hebetata Bailey; Scherer et al., 2000, p. 436, pl. 3, figs. 6, 7.

Rhizosolenia hebetata f. hiemalis Gran sensu Schrader, 1973, p. 709, pl. 9, figs. 11, 13-17, 19-21, 24, 25; Schrader, 1976, p. 635, pl. 9, figs. 1-3; Akiba, 1986, p. 444, pl. 17, figs. 10, 11; pl. 18, figs. 9, 10; Harwood and Maruyama, 1992, p. 11, fig. 7.

Remarks: Rhizosolenia hebetata f. hiemalis and R. hebetata f. hiemalis-spinosa identified by Schrader (1976) are included together here.

Rhizosolenia styliformis Brightwell; Schrader, 1973, p. 710, pl. 9, fig. 9(?); pl. 10, figs. 1, 18-21.

Rhizosolenia sp. cf. R. sima f. silicea Sundström; Bohaty et al., 1998, p. 444, pl. 5, figs. 1, 2.

Synonym: Rhizosolenia sp. D of Harwood and Maruyama, 1992, p. 705, pl. 18, figs. 7-10; Mahood and Barron, 1996b, p. 292, pl. 1, figs. 4a-5b; pl. 7, fig. 3.

Remarks: See notes regarding this form in Bohaty et al., 1998.

Rocella gelida (Mann) Bukry; Gombos and Ciesielski, 1983, p. 604, pl. 6, figs. 1-6; pl. 26, fig. 1.

Rocella gelida var. schraderi (Bukry) Barron, 1983, pp. 511, 512, pl. 4, fig. 10.

Basionym: Rocella schraderi Bukry, 1978, p. 788, pl. 6, figs. 1-10; pl. 7, fig. 1; Gombos and Ciesielski, 1983, p. 604, pl. 22, fig. 6.

Rocella praenitida (Fenner) Fenner in Kim and Barron; Harwood and Maruyama, 1992, p. 705, pl. 4, figs. 1-3, 5.

Rocella vigilans var. B of Harwood and Maruyama, 1992, p. 705, pl. 4, figs. 13, 14.

Rouxia antarctica Heiden in Heiden and Kolbe; Schrader, 1976, p. 635, pl. 5, figs. 1-8; Mahood and Barron, 1996b, p. 292, pl. 2, figs. 5, 6; pl. 7, figs. 18, 19; Zielinski and Gersonde, 2002, p. 261, pl. 2, fig. 10.

Rouxia californica Peragallo; Schrader, 1973, p. 710, pl. 3, figs. 18-20, 22(?), 26; Baldauf and Barron, 1991, p. 590, pl. 5, fig. 6.

Rouxia heteropolara Gombos; Gombos, 1977, p. 597, pl. 7, figs. 14, 15.

Rouxia isopolica Schrader, 1976, pp. 635, 636, pl. 5, figs. 9, 14, 15, 20.

Rouxia leventerae Bohaty, Scherer, and Harwood, 1998, pp. 444, 445, pl. 1, figs. 1-6; Zielinski and Gersonde, 2002, p. 261, pl. 2, figs. 1-7.

Rouxia naviculoides Schrader, 1973, p. 710, pl. 3, figs 27-32; Zielinski and Gersonde, 2002, p. 261, pl. 2, figs. 8, 9.

Rouxia peragalli Brun and Héribaud sensu Baldauf and Barron, 1991, p. 590, pl. 5, figs. 7, 8.

Rouxia sp. 1 (Pl. P2, fig. 14; Pl. P3, figs. 7, 8).

Description and Remarks: Rouxia sp. 1 is small (~40 µm in length) with a linear valve outline and rounded ends. The length of each raphe covers approximately one-fourth of the apical length of the valve. This form was noted in three upper Pliocene samples from Hole 1138A.

Spumorbis annulifer Komura, 1998, pp. 5, 6, figs. 17-19, 69-86.

Stellarima microtrias (Ehrenberg) Hasle and Sims; Hasle et al., 1988, pp. 196-198, figs. 1-25.

Stellarima stellaris (Roper) Hasle and Sims; Hasle et al., 1988, pp. 198-200, figs. 26-38.

Synedropsis sp. B

Synonym: "Tigeria" sp. B of Scherer et al., 2000, p. 440, pl. 2, fig. 15 (Pl. P2, fig. 12).

Thalassionema nitzschioides (Grunow) Mereschkowsky; Hasle, 2001, pp. 9-16, figs. 1-3, 5-25, 27.

Thalassionema nitzschioides var. parvum Heiden; Hasle, 2001, pp. 9-16, figs. 4, 26.

Thalassionema nitzschioides var. 1

Description and Remarks: Thalassionema nitzschioides var. 1 has one apical end that is inflated. This form is present in the upper Miocene-lower Pliocene section of Hole 1138A.

Thalassiosira antarctica Comber; Krebs, 1983, p. 286, pl. 5, fig. 4a-f; Johansen and Fryxell, 1985, p. 158, figs. 15-17, 37-39.

Thalassiosira bipora Shiono, 2000b, pp. 139-143, figs. 25-44 (Pl. P1, fig. 1).

Remarks: See discussion under Thalassiosira tetraoestrupii.

Thalassiosira complicata Gersonde, 1991, pp. 150, 151, pl. 1, figs. 1, 2; pl. 5, figs. 18-20; pl. 6, figs. 1-6; pl. 7, figs. 1-5.

Thalassiosira sp. cf. T. eccentrica (Ehrenberg) Cleve; Fryxell and Hasle, 1972, p. 300, figs. 1-18 (Pl. P1, fig. 6).

Thalassiosira elliptipora (Donahue) Fenner ex Mahood and Barron, 1996b, pp. 292-294, pl. 4, fig. 3; pl. 5, figs. 4a-7c; pl. 8, fig. 6.

Thalassiosira fasciculata Harwood and Maruyama, 1992, p. 707, pl. 15, figs. 4-6; Mahood and Barron, 1996a, p. 287, figs. 15-24, 27, 28.

Thalassiosira gracilis (Karsten) Hustedt; Johansen and Fryxell, 1985, pp. 168-170, figs. 8, 58, 59.

Remarks: T. gracilis var. gracilis and T. gracilis var. expecta are grouped together in the present study.

Thalassiosira insigna (Jousé) Harwood and Maruyama, 1992, p. 707, pl. 14, figs. 3-5; Zielinski and Gersonde, 2002, p. 264, pl. 5, figs. 14, 15 (Pl. P1, fig. 4).

Remarks: The current usage of "Thalassiosira insigna" for Pliocene specimens from the Southern Ocean is incorrect (D. Harwood, pers. comm., 2002). The basionym for this taxon, Cosmiodiscus insignis Jousé, was described from the North Pacific samples (Jousé, 1977) and is better placed within the family Hemidiscaceae, not Thalassiosiraceae, based on the presence of a marginal ring of labiate processes and the absence of strutted processes. The Southern Ocean forms, however, possess strutted processes and, therefore, should be given a separate name within the Thalassiosiraceae (pers. comm. I. Makarova to D. Harwood, 1999). In the current study, we apply the taxonomy of Harwood and Maruyama (1992) and continue the (incorrect) usage of T. insigna. Only specimens with an entirely hyaline central area (i.e., nonperforated) are included here as T. insigna. Morphologies with a perforated central area are recorded as Thalassiosira sp. 1 (see below).

Thalassiosira inura Gersonde, 1991, p. 151, pl. 6, figs. 7-14; pl. 8, figs. 1-6; Gersonde and Burckle, 1990, p. 782, pl. 3, figs. 15-17; pl. 5, fig. 14; Harwood and Maruyama, 1992, p. 707, pl. 14, figs. 12-16.

Thalassiosira jacksonii Koizumi and Barron in Koizumi; Baldauf and Barron, 1991, p. 591, pl. 6, fig. 7.

Thalassiosira kolbei (Jousé) Gersonde, p. 793, pl. 1, fig. 2; pl. 5, figs. 3, 5, 6; Fenner, 1991, p. 108, pl. 1, figs. 1, 4; pl. 2, figs. 3, 4; Mahood and Barron, 1996b, p. 294, pl. 4, figs. 1, 2; pl. 8, fig. 1a, b.

Thalassiosira lentiginosa (Janisch) Fryxell; Mahood and Barron, 1996b, p. 294, pl. 4, figs. 4a, b, 5; pl. 8, fig. 2a, b.

Remarks: The first occurrence of T. lentiginosa could not be determined with certainty in Hole 1138A. Early forms of this taxon appear to intergrade with Thalassiosira striata. Both T. lentiginosa and T. striata possess strutted processes that are scattered across the valve face, and some lower to middle Pliocene specimens of T. striata possess a large labiate process that is radially oriented on the valve margin—a diagnostic feature of T. lentiginosa. SEM work is needed to clarify the taxonomic differences between T. lentiginosa and T. striata.

Thalassiosira lentiginosa var. obovatus (Castracane) Fryxell

Synonym: Coscinodiscus lentiginosus f. obovatus (Castracane) Ciesielski, 1983, p. 653, pl. 4, figs. 6-8.

Thalassiosira miocenica Schrader; Barron, 1985a, p. 445, pl. 5, fig. 6; Barron, 1985b, p. 792, fig. 11.11; Gersonde and Burckle, 1990, p. 782, pl. 3, figs. 4, 5; Baldauf and Barron, 1991, p. 591, pl. 6, fig. 2.

Thalassiosira nansenii Scherer and Koç, 1996, p. 89, pl. 4, figs. 1-5.

Thalassiosira oliverana (O'Meara) Makarova and Nikolaev; Mahood and Barron, 1996b, pl. 5, figs. 1-3; pl. 8, figs. 3-5.

Remarks: Specimens identified as T. oliverana in the present study represent a complex group of morphologies with both coarse and fine areolation. Forms with a central "dimple" (see Harwood and Maruyama, 1992, pl. 14, figs. 11, 17) and small diameter (40 µm) are also included here as T. oliverana. Specimens of T. oliverana var. sparsa (see Harwood and Maruyama, 1992, p. 708, pl. 16, fig. 13) were recorded separately (Table T1).

Thalassiosira oliverana var. sparsa Harwood and Maruyama, 1992, p. 708, pl. 16, fig. 13; Censarek and Gersonde, 2002, p. 353, pl. 5, figs. 1, 2.

Thalassiosira praefraga Gladenkov and Barron, 1995, pp. 30, 31, pl. 2, figs. 3-6, 9; Scherer et al., 2000, p. 440, pl. 2, figs. 3, 7.

Thalassiosira ritscheri (Hustedt) Hasle; Johansen and Fryxell, 1985, p. 176, figs. 14, 56, 57.

Thalassiosira striata Harwood and Maruyama, 1992, p. 708, pl. 15, figs. 7-9; Zielinski and Gersonde, 2002, p. 264, pl. 4, fig. 7.

Remarks: See discussion under Thalassiosira lentiginosa.

Thalassiosira tetraoestrupii Bodén, 1993, p. 63, pl. 1, figs. A-G; pl. 2, figs. A, B, H, J; Mahood and Barron, 1995, figs. 9-19, 25, 26, 28-46.

Remarks: The occurrence chart for the Neogene section of Hole 1138A includes a column identified as the "Thalassiosira tetraoestrupii group" (Table T1). This group most likely includes several species that possess a central strutted process and a labiate process on the valve face. Thalassiosira tetraoestrupii var. reimeri was recorded separately. Several similar species from the broadly defined "Thalassiosira trifulta group" have been recently described from Pliocene-Pleistocene sediments of the North Pacific (Shiono, 2000b, 2001). These taxa have not yet been identified in Southern Ocean, but several within this group are most likely present in upper Miocene-lower Pleistocene sediments on the Kerguelen Plateau. Common specimens in Section 183-1138A-8R-5 (see Pl. P1, fig. 1) are tentatively identified as Thalassiosira bipora (Shiono, 2000b, pp. 139-143, figs. 25-44), but SEM observations are required to confirm this identification.

Thalassiosira tetraoestrupii var. reimeri Mahood and Barron, 1995, p. 2, figs. 1-8, 20-24, 27.

Remarks: T. tetraoestrupii var. reimeri has a narrow, consistent range in the upper Pliocene of Hole 1138A (Table T1). A few rare specimens, however, were also identified in the lower Pleistocene; these occurrences may indicate a longer total range for this taxon, or they may be reworked.

Thalassiosira torokina Brady, 1977, p. 123, figs. 1-5; Scherer, 1991, pl. 2, fig. 4; Mahood and Barron, 1996b, p. 296, pl. 6, figs. 1-3; pl. 8, fig. 8.

Remarks: Bohaty et al. (1998) describe and illustrate a "late form" of T. torokina with a reduced number of central processes from Pleistocene strata recovered in McMurdo Sound, Ross Sea. "Early forms" of T. torokina with numerous central processes (Scherer, 1991; Mahood and Barron, 1996b) were observed only in the Pliocene interval of Hole 1138A. "Late forms" of T. torokina were not observed in Hole 1138A and, thus, may have been restricted to colder shelf and shelf margin areas during the Pleistocene. It is also possible that these two forms represent separate species.

Thalassiosira trifulta Fryxell in Fryxell and Hasle; Johansen and Fryxell, 1985, p. 176, figs. 12, 65, 66.

Thalassiosira tumida (Janisch) Hasle in Hasle et al.; Fenner et al., 1976, p. 780, pl. 10, figs. 6, 7; Johansen and Fryxell, 1985, pp. 176, 177, figs. 28-32.

Thalassiosira vulnifica (Gombos) Fenner, 1991, p. 108, pl. 2, fig. 2; Mahood and Barron, 1996a, pp. 285-287, figs. 1-14, 25, 26.

Thalassiosira sp. 1 (Pl. P1, fig. 5)

Description and Remarks: Thalassiosira sp. 1 is an intermediate form between T. insigna and T. oliverana. It is characterized by a perforated hyaline central area and the valve diameter is generally smaller than T. insigna. A distinctive process between the hyaline area and valve margin is also present on some specimens (Pl. P1, fig. 5). A similar specimen with a perforated hyaline are was referred as Cosmiodiscus intersectus (Brun) Jousé by Gersonde and Burckle (1990, p. 780, pl. 4, fig. 13). The Antarctic specimens of "C. intersectus," however, have been put in synonymy with T. oliverana var. sparsa by Harwood and Maruyama (1992). It is possible that "Thalassiosira sp. 1" identified in Hole 1138A is referable to T. oliverana var. sparsa, but a prominent strutted process outside of the central hyaline area has not been previously documented on T. oliverana var. sparsa specimens.

Trinacria excavata Heiberg; Gombos and Ciesielski, 1983, p. 605, pl. 17, fig. 8.