Abstract

Here we present new observations of Spiniferites alaskensis, a relatively rare species described from the Eemian of the Gulf of Alaska. We show that the species shows a gonyaulacacean tabulation: Po, 4´, 6´´, 6c,? s, 6´´´, 1p, 1´´´´. The surface is finely granulate to scabrate. The species bears characteristic processes: these are exclusively gonal, membranous, perforated and end distally in platforms with stumpy ends. We provide more detail as how this species compares to closely related species belonging to the genus Spiniferites.

Introduction

Spiniferites alaskensis Marret et al. 2001 ex Marret in Fensome and Williams (2004) was first identified in the North East Pacific Ocean, in the Eemian interval that was recovered during the ODP Leg 145, site 887B (54°21’ N – 148°23’ W, 3647 m water depth) (Marret et al. 2001). The name was validated by Fensome and Williams (2004) because Marret et al. (2001) did not indicate which of the illustrations represented the holotype. The original description of this taxon mentioned a chorate cyst of ovoid shape with an apical boss, thin cyst wall, a finely granulate surface, gonal and broad terminally trifurcate processes, low sutural septa between the processes and a gonyaulacacean tabulation. This taxon was described as differing from other known Spiniferites only by the shape of the processes and their pointed-end termination.

New observations have been carried out, using a combination of light-transmitted and scanning electron microscopy, enabling to fully characterise the morphology of this relatively unknown species.

Material and methods

Permanent slides made from residues prepared by Marret et al. (2001) from the type locality (ODP Leg 145 core 887B, section 2H5 at 65 cm in section, Gulf of Alaska) were examined using a light microscope at Geotop, Montreal, Canada (Leica DMR equipped with a Leica DFC490 digital camera). Single specimens were picked under an inverted microscope with a micropipette and observed using a scanning electron microscope (Hitachi S-3400N SEM) at Geotop, Montreal, Canada. Kofoid’s nomenclature is used to designate the plates.

Results

Division DINOFLAGELLATA (Bütschli 1885) Fensome et al. 1993, emend. Adl et al. 2005

Class DINOPHYCEAE Pascher 1914

Subclass PERIDINIPHYCIDAE Fensome et al. 1993

Order GONYAULACALES Taylor 1980

Suborder Gonyaulacineae autonym

Family Gonyaulacaceae Lindemann 1928

Subfamily Gonyaulacoideae autonym

Genus Spiniferites Mantell 1850, emend. Sarjeant 1970

Spiniferites alaskensis Marret et al. 2001 ex Marret in Fensome and Williams 2004

Plate 1, Figures 1–10; Plate 2, Figures 1–6.

Synonymy. None.

Holotype. Marret et al. 2001, their Plate 1, Figures 7–9.

Locus typicus. ODP core 887B, section 2H5 at 65 cm in section, Gulf of Alaska.

Stratum typicum. Sediments deposited during isotope stage 5e in the Gulf of Alaska (ODP Leg 145, site 887) northeastern North Pacific.

Etymology. Named alaskensis from its type locality in the Gulf of Alaska, NE Pacific (Marret et al. 2001).

Distinguishing characters. Ovoid to pear shaped cysts with an apical boss (Plate 1, Figures 4–6) that touches all the apical plates (Plate 1, Figure 1). The cyst wall is thin (less than 1 µm) and has a finely granulate to scabrate wall surface, which is confirmed by SEM observation (Plate 2, Figures 1–4). This surface texture continues on the bases of processes and the bases of the connecting crests of the processes (Plate 2, Figure 2), but not on the more distal part, which is smooth to shagreenate (Plate 2, Figures 5–6). Processes are exclusively gonal, stout, membranous, with perforated polygonal platforms with stumpy distal ends (Plate 2, Figures 5–6). Processes at the junctions of the apical plates are shorter compared to others, and those along 1´´´´ are the longest. The processes do not bear granules, as opposed to the sutural septa connecting the processes. These sutural septa define a gonyaulacacean tabulation: Po, 4´, 6´´, 6c,? s, 6´´´, 1p, 1´´´´ (Plate 1, Figures 1, 3). The tabulation is expressed with a generally low sutural arrangement, with slightly undulating sutures (Plate 1, Figure 7), except being high where they connect cingular processes (arrow “a”), between 1´, 4´ and as (arrow “b”), between 6´´´ and 1´´´´ (arrow “c”), and between 1p and 1´´´´ (arrow “d”) (Plate 1, Figure 10). Observation of the epicyst shows an arrangement of four apical and six precingular plates (Plate 1, Figure 1), and for the hypocyst, six postcingular plates although 1´´´ is not well expressed, 1p, and an asymmetrical 1´´´´. The cingular arrangement shows six plates, with a typical displacement of one cingular width, without overhang. In the sulcal area, a pronounced suture is observed above ps and below as. The other sulcal plates are not well reflected. The archeopyle has a pentagonal shape, corresponding to the third precingular plate (3´´), with rounded angles, and is reduced and free (Plate 1, Figure 8).

Dimensions. Central body diameter length 26.3 (31.4) 36.8 µm and width 23.6 (29.3) 31.5 µm with length of processes 7.5 (10.1) 12.5 µm (Marret et al. 2001). Number of specimen measured: 11

Biological affiliation. Unknown.

Comparison to other taxa.Spiniferites alaskensis shows some similarities to a number of Spiniferites species, such as Spiniferites ludhamensis Head 1996 which has a similar shape and stout processes, but Spiniferites ludhamensis has hollow processes, and the cyst has a thicker wall and no apical boss (Head 1996). Spiniferites ristingensis Head 2007 and Spiniferites delicatus Reid 1974 also have membranous processes with petaloid distal ends.

However, Spiniferites ristingensis has small, densely distributed blisters and hollow undulations over the surface (comparable to “bubble–wrap”) (Head 2007). Spiniferites delicatus has a granular surface, with high sutural crests (Reid 1974). Spiniferites bentorii (Rossignol 1964) Wall & Dale 1970 also has a pear shaped body, with an apical boss, but has processes often with claustra at their base and these processes are not membranous.

Spiniferites belerius Reid 1974 can also have an oval to pear shaped body, but has a shorter apical boss, its wall surface is not as granular and there is a larger cingulum displacement, and has box-like processes (Reid 1974). Spiniferites alaskensis also differs from Spiniferites falcipedius Warny and Wrenn 1997, as the latter has hollow processes, no apical boss and high crests between the antapical processes (Warny and Wrenn 1997). Lastly, Spiniferites alaskensis is distinguished from Spiniferites lazus Reid 1974 as the latter has a clearly elongated ovoidal shape and claustra at the base of the processes (Reid 1974).

Acknowledgements

We like to thank Anne de Vernal for use of microscope facilities at GEOTOP. Maryse Henry and Raynald Lapointe are acknowledged for help with SEM preparations at GEOTOP. We also are very grateful for the constructive comments from reviewers Laurent Londeix and André Rochon that helped to improve the manuscript.

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