Trilobatus sacculifer
Creators: name: Poole, Christopher R.
name: Wade, Bridget S.
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Chromista
Foraminifera
Globothalamea
Rotaliida
Globigerinidae
Trilobatus
Trilobatus sacculifer

description: Trilobatus sacculifer (Brady, 1877)   
(Figs 8L–P, 9, 10, 11A–J, 12D, E, 14A, 16A–D, 17D, H)  
 1862 Globigerina helicina d’ Orbigny; Carpenter, Parker & Jones: pl. 12, fig. 11 [note: not valid species name as ‘ Globigerina helicina ’ was used by d’ Orbigny for a different species concept; see remarks].   
 1877 Globigerina sacculifera Brady: 535 [original description but not illustrated].   
 1884 Globigerina sacculifera Brady: 604, pl. 80, figs 11–17 and pl. 82, fig. 4 [numerous samples from the Challenger Expedition; illustrations reproduced in Jones (1994)].   
 1940 Globigerinoides sacculifera (Brady); Coryell & Rivero: 340, pl. 42, figs 24, 25, 32.   
 1954 Globigerinoides sacculifera (Brady); Cushman, Todd & Post: 369, pl. 91, fig. 7.   
 1957 Globigerinoides triloba sacculifer (Brady); Bolli: 113, pl. 25, figs 5a–6.   
 1959 Globigerinoides triloba sacculifera (Brady); Blow: 188, pl. 11, fig. 63a, b.   
 1964 Globigerinoides triloba sacculifera (Brady); LeRoy: F42, pl. 14, fig. 18.   
 1967 Globigerinoides quadrilobatus sacculifer (Brady); Closs: 340, pl. 1, fig. 21.   
 1970 Globigerinoides trilobus sacculifer (Brady); Bolli: 626, pl. 1, fig. 5.   
 1983 Globigerinoides sacculifer (Brady); Pujol & Duprat: 612, pl. 4, figs 4, 5.   
 1983 Globigerinoides sacculifer (Brady); Kennett & Srinivasan: 66, pl. 14, figs 4–6.   
 1994 Globigerinoides sacculiferus (Brady); Loeblich & Tappan: 107, pl. 205, figs 1–3, 7–9   
 2006 Globigerinoides sacculifer (Brady); Williams, Schmidt, Wilkinson, Miller & Taylor: 154, pl. 1, figs 1–11.   
 Description. Type of wall: spinose, normal perforate, coarsely cancellate (often termed polygonal or honeycomb) ‘ sacculifer -type’ wall texture. Test morphology: low trochospire, initially involute, later more evolute coiling, coiling direction random, three to four chambers in the final whorl, rapidly enlarging, adult chambers typically globose, near-spherical, until the last chamber, which is a flattened, sac-like shape exhibiting extreme variation in size and shape; sutures distinct, depressed, straight to slightly curved on both sides; umbilicus narrow to moderate; primary aperture umbilical, sometimes umbilical-extraumbilical, a low–medium arch, often broad and/or asymmetrical, with bordering imperforate lip; numerous supplementary apertures on spiral side, one per chamber, placed at the sutures of the preceding chamber and third-previous chamber.   
Note: description is based on the original description and species concept of Brady (1877, p. 535), and also those of Brady (1884, p. 604), Banner & Blow (1960, p. 22) and Kennett & Srinivasan (1983, p. 65), but is here emended and extended.  
 Remarks. Trilobatus sacculifer is distinguished from T. trilobus, T. immaturus and T. quadrilobatus by the presence of a distinctive flattened, sac-like chamber which is often elongate or lobate; the other three morphospecies possess only globose, (near-)spherical chambers throughout all adult chambers. It also differs from these morphotypes by the presence of a distinct lip bordering the primary aperture. Trilobatus sacculifer differs from G. fistulosa by the lack of clear protuberances on any of the final chambers, although the final chamber may be lobate.   
 Type locality. The type material for T. sacculifer is from a loose ‘chalk’ block, from New Ireland, Papua New Guinea (Brady 1877). The ‘chalk’ block was in fact a fragment of a carved figure, made by local inhabitants of the island and obtained by missionary Reverend G. Brown (Brown 1877; pp. 140–141; see also Liversidge 1877; Parker 1967). Rather than being sourced from the mainland itself, the ‘chalk’ block was actually derived from seafloor deposits, where it had been extruded, apparently by earthquakes (Brown 1877) and/or volcanic activity (Brady 1884), onto the shore and then used by local inhabitants for a carved figure. The surrounding seafloor deposits off New Ireland indeed contain such ‘chalk’ material (e.g. Exon et al. 1986), and are likely the source of the type material for T. sacculifer.   
 Taxonomic history. Brady (1877) observed that despite a specimen with a sac-like final chamber having been previously illustrated by Carpenter et al. (1862, pl. 12, fig. 11) under the name Globigerina helicina d’ Orbigny, the helicina form had actually been described to represent a very different morphology (typically viewed as a morphological variant of Globigerinoides ruber). Hence, Brady (1877) erected the new species, Globigerina sacculifera, and provided a brief description. Though not illustrated by Brady (1877), a more detailed description and accompanying illustrations of ideotypic specimens were provided subsequently in Brady (1884, pl. 80, figs 11–17 and pl. 82. fig. 4; see also corresponding figures in Jones 1994). The subsequent illustrations were from North Pacific ‘Challenger Expedition’ material, rather than from the original type material of New Ireland, Papua New Guinea. However, the syntypic suite of specimens of Brady (1877) were subsequently examined by Banner & Blow (1960), including description and designation of a lectotype. Interestingly, the line drawings (pl. 4, fig. 1a, b) of their selected lectotype showed no lip or rim bordering the primary aperture, and their description specifically states its absence (Banner & Blow 1960, p. 22), despite this being a diagnostic character of the morphospecies (e.g. Kennett & Srinivasan 1983; this study). Williams et al. (2006) presented the first SEM images of Banner & Blow’ s lectotype (reproduced here in Fig. 17). Their SEM images of the lectotype and paralectotypes clearly resolve the matter, as each possesses a lip.   
 After Cushman (1927) erected Globigerinoides, sacculifer was accordingly placed in this genus by subsequent authors because it exhibits multiple supplementary apertures, although see various nomenclatural combinations in the synonymy list. Following Spezzaferri et al. (2015), sacculifer has been transferred to the new genus, Trilobatus, and we adhere to this designation.   
 The large morphological variation in the sac-like final chamber of T. sacculifer has been widely acknowledged, including kummerform (similar to the T. subsacculifer Cita, Premoli Silva & Rossi morphospecies), lobate, tapering and pointed morphologies. Todd (1964, p. 1073) recognized not only the biostratigraphical potential of G. fistulosa, but also the lack of biostratigraphical value in forms with simply lobate chambers (i.e. ‘incipient protuberances’). Sac-like chambers that are lobate and/or have incipient protuberances have little biostratigraphical value as they have approximately the same stratigraphical range as T. sacculifer sensu stricto, which extends from the lower Miocene to Recent (see also Belford 1988). However, we observe that forms with incipient protuberances do increase in abundance during the stratigraphical range of G. fistulosa (mid-Pliocene to early Pleistocene). Irregular final chambers and aberrant morphologies are common to all morphospecies of planktonic foraminifera (Mancin & Darling 2015), but are generally not treated any differently to ‘normal’ specimens in terms of taxonomy. For example, incipient protuberances also occur in unrelated morphospecies such as Globigerina bulloides (Mancin & Darling 2015, pl. 3, fig. 3) and Globigerinoides ruber (Hanagata & Nobuhara 2015, fig. 20.9), but are not considered distinct morphospecies.   
 Although there is morphological gradation between T. quadrilobatus and T. sacculifer (i.e. forms with final chambers of intermediate morphology between spherical and flattened sac-like chambers), all T. sacculifer sensu stricto possess a distinct lip on the primary aperture (see description) even if it is a kummerform specimen.   
 Wall cross-sections: although the spine holes and primary wall texture are often obscured by gametogenic calcite, cross-sectional views of the wall of T. sacculifer show relict spines present. The specimens in this study are relatively large planktonic foraminifera, particularly some T. sacculifer specimens and virtually all Globigerinoidesella fistulosa, which are regularly more than 1 mm in size. These large specimens produce walls which can be at least 40 Lm thick (Fig. 9Q, R), even those with thin or no gametogenic calcite.   
  Notes on the ‘ subsacculifer’ morphospecies.  Globigerinoides sacculifer subsacculifera Cita, Premoli Silva & Rossi, 1965 was erected for specimens of similar gross morphology to T. sacculifer, but possessing a smaller test and less-developed sac-like final chamber. The last chamber is elongated, but not as pointed and protruding as in T. sacculifer (Cita et al. 1965). Spezzaferri et al. (2015) transferred subsacculifer to the new genus Trilobatus.   
 However, subsequent to the original description, T. subsacculifer has only been rarely recorded despite its apparent biostratigraphical utility, as the stratigraphical range was reported as early Miocene to early–middle Miocene by Spezzaferri (1994). Few succeeding observations of T. subsacculifer exist, but reported occurrences include Bizon & Bizon (1972, p. 242, figs 1–4), Rogl (1975), Poignant & Pujol (1978, p. 673, pl. 12, figs 11, 12), Fordham (1986), Spezzaferri (1994, pl. 13, fig. 3a–c), Coccioni et al. (1997), Odin et al. (1997), Spezzaferri et al. (2002) and Gennari et al. (2013). Spezzaferri et al. (2002, p. 245) listed T. subsacculifer as a warm-water planktonic indicator. Their supposition receives support from the stable isotope analyses of T. subsacculifer by Bicchi et al. (2003), which show that T. subsacculifer probably had a similar depth ecology to modern T. sacculifer. Cita et al. (1965) suggested T. subsacculifer may represent the ancestral stock for T. sacculifer.   
 Here, we report examples similar in morphology to T. subsacculifer, but from the Pliocene–Pleistocene (i.e. considerably later than the highest occurrence reported by Spezzaferri 1994). Although T. sacculifer is far more common in the same samples, smaller forms akin to the T. subsacculifer morphology are present in each site investigated (ODP Sites 871, 926, 1115, and GLOW samples). The final chamber is generally diminutive (regularly kummerform), with a less-developed sac-like shape, and the specimens are smaller than typical T. sacculifer. We regard these specimens simply as phenotypic variants of T. sacculifer, forming an end member of the large intraspecific variability in this morphospecies. Even the small sac-like chambers have an imperforate lip that borders the aperture, which is a characteristic property of T. sacculifer. Thus T. subsacculifer may be a junior synonym of T. sacculifer, but further work from Miocene samples is required.
description: Published as part of Poole, Christopher R. & Wade, Bridget S., 2019, Systematic taxonomy of the Trilobatus sacculifer plexus and descendant Globigerinoidesella fistulosa (planktonic foraminifera), pp. 1989-2030 in Journal of Systematic Palaeontology 17 (23) on pages 2013-2017, DOI: 10.1080/14772019.2019.1578831, http://zenodo.org/record/10883327