Spiniferites cruciformis,Pterocysta cruciformisandGaleacysta etrusca: morphology and palaeoecology

Abstract

Miocene to modern sediments of the Ponto-Caspian basins and Mediterranean Sea are uniquely distinguished by presence of gonyaulacacean cysts with ellipsoid to cruciform endocysts and highly variable ectocystal features, including pterate (wing-like) and galeate (helmet-like) outer wall layers. The term cruciform is defined to indicate cysts with concave epicyst and hypocyst surfaces and moderate dorsoventral flattening. These features may be morphological responses to salinity stress and some biometrical studies conclude that the cruciform Ponto-Caspian species Spiniferites cruciformis of Wall and Dale 1973 and Pterocysta cruciformis Rochon et al. 2003 are morphotypes of the ellipsoidal-subpentagonal Miocene-Holocene species Galeacysta etrusca Corradini and Biffi 1988. We show that the holotypes of these cruciform and rhomboid-subpentagonal galeate taxa differ in endocyst shape, ectocyst structure and attachment points, process morphology, and sulcal plate expression, and we present new data on morphological variations, modern distribution and ecology. We list multiple criteria for distinguishing these taxa from Paratethyan dinoflagellates with shared features, including Thalassiphora spp., Lophocysta, Romanodinium, and Seriliodinium. Log transforms of endocyst:ectocyst (EN:EC) dimensions cannot fully capture cruciformness or galeate and pterate wall characteristics that distinguish the genera, and at DSDP Site 380, EN:EC values for Pleistocene populations of Spiniferites cruciformis and Galeacysta etrusca are significantly different. Re-examination of the history of studies on the Galeacysta etrusca complex and comparison with new studies of Pleistocene to recent cysts leads to the conclusion there is insufficient evidence to justify combining the cruciform species with Galeacysta etrusca and we provide criteria for distinguishing among the main components of the complex. Using multiple morphological features, it appears there is a replacement of large Palaeogene marine-brackish water camocavate-circumcavate taxa with elliptical endocysts first by the Miocene rhombo-subpentagonal galeate species Galeacysta etrusca and then by the Pliocene-Holocene semi-marine-brackish cruciform species Spiniferites cruciformis and stenohaline Pterocysta cruciformis.

The dinoflagellate cyst generaAchomosphaeraEvitt 1963 andSpiniferitesMantell 1850 in Pliocene to modern sediments: a summary of round table discussions

“…There was general agreement that this is not a Spiniferites species and therefore we retain it in Thalassiphora. Mudie et al (2018) found no intergradation in morphology between Thalassiphora balcanica and Galaecysta etrusca other than possibly some overlap at the upper end of their endocyst-ectocyst size and these authors agree to retain Thalassiphora balcanica. PJM stated that the location of the holotype (Balteş's specimen L/C.…”

“…PJM added a note after the workshop that there is agreement among herself, AR, LL and Shannon Ferguson that the species Spiniferites cruciformis, Pterocysta cruciformis and Galeacysta etrusca belong to separate genera and do not intergrade; AG notes during drafting that he agrees. This species and related taxa are further discussed by Mudie et al (2018), who provide definitions for the terms cruciform, galeate and pterate, as well as a table of characteristics distinguishing these and other taxa grouped in the so-called Galeacysta etrusca complex of Popescu et al (2009). MJH in draft provided the following information: Although preserved as a single grain mount, the holotype is desiccated making any detailed observations impossible.…”

“…Balteş described the central body as having a vaguely outlined cingulum, and a trapezoidal cingular archeopyle, but otherwise lacking tabulation. However, S€ ut} o-Szentai (2000, p. 162) transferred Thalassiphora balcanica to Spiniferites as S. balcanicus, based on specimens from Upper Pannonian deposits in boreholes from Hungary, some of which are illustrated as having highly reduced, undecipherable ornamentation and others with fenestrate luxuria and attachments like those of Galeacysta etrusca (see Mudie et al 2018). The emended diagnosis of S€ ut} o-Szentai 2000for Spiniferites balcanicus describes an ovoid or spheroidal central body with two membranes "fixed both on the right and left side of the sulcus" and sometimes with two winglike membranes that are "differently perforated", one of them being arched in the apical area and being partially connected except in the ventral area.…”

Palynology and micropalaeontology of the Pliocene - Pleistocene transition in outcrop from the western Caspian Sea, Azerbaijan: Potential links with the Mediterranean, Black Sea and the Arctic Ocean?

“…Bobrov et al, 1983;Alyoshina, 1972, 1978). Dinocysts and NPP were identified from numerous sources including Bakrač et al (2012), Baltes (1971), Evitt et al (1985), Marret et al (2004), Mudie et al (2011) , Mudie et al (2017Mudie et al ( , 2018, Richards et al (2014Richards et al ( , 2017, Soliman and Riding (2017), Sütő-Szentai (1982, 2010 and Wall et al (1973).…”

Introduction toSpiniferitesMantell 1850 special issue

“…The genera Galeacysta Corradini and Biffi 1988, Seriliodinium Eaton 1996and Pterocysta Rochon et al 2002 are closely related to the cruciform species Spiniferites cruciformis Wall and Dale in Wall et al 1973 and form a peculiar group of morphologies. These are discussed in more detail by Mudie et al (2018).…”