THALASSIONEIS SIGNYENSIS (BACILLARIOPHYCEAE) FROM NORTHWEST WEDDELL SEA ICEBERGS, AN EMENDATION OF THE GENERIC DESCRIPTION¹

Abstract

We offer an emended description of the genus Thalassioneis based on new observations of the type species, T. signyensis Round, from material sampled in the northwest Weddell Sea. Specimens from algal communities attached to submerged flanks of several icebergs were collected with a remote-operated vehicle (ROV-Phantom DS 2). The analyses were carried out by LM and SEM. Fresh material and frustules without organic matter allowed us to observe details not included in the original description such as type and structure of colonies and chloroplasts. The frustule shows an asymmetry with respect to the location of the apical pore fields, one of them situated on the valvar face and the other one displaced toward the mantle; the former is involved in joining contiguous cells to form long chains. Furthermore, we present details on the ultrastructure of the cingulum that consists of three to four open copulae with one or more rows of poroids. A brief discussion on the habit and ecology of this taxon, which may be endemic to the northwest Weddell Sea, is also presented. A comparison with similar genera, such as Brandinia, Creania, Fossula, Fragilaria, Rimoneis, Synedropsis, and Ulnaria, is included with an evaluation of morphological characteristics useful to differentiate them.

Diatoms (Bacillariophyceae) associated with free-drifting Antarctic icebergs: taxonomy and distribution

“…Beyond its influence on ocean physics, sea ice provides diverse habitats for countless organisms (Horner 1995;Knox 2007). Recent studies by Smith et al (2007), Robison et al (2011) and Ferrario et al (2012) have also reported diatom communities living on submerged vertical walls of free-drifting Antarctic icebergs, as introduced previously by Whitaker (1977) for grounded icebergs. These diatoms are believed to feed the krill population in the vicinity .…”

“…Similarly, the pennate Thalassioneis signyensis was reported by Robison et al (2011) and Ferrario et al (2012) as the dominant diatom species associated with free-drifting icebergs.…”

“…punctata and Nitzschia aff. decipiens by light microscopy (Smith et al 2007) were later conclusively identified as T. signyensis by Ferrario et al (2012) using scanning electron microscopy. This species shows a large range of cell shapes and sizes, with the apical axis varying from 12.5 to 60.0 lm and the transapical axis from 5.0 to 9.5 lm (Ferrario et al op.…”

“…Likewise, various terms and criteria have been used to describe both the organisms that integrate these communities as well as their habitats (Horner et al 1988(Horner et al , 1992Garrison 1991). Particularly for the diatom T. signyensis associated with icebergs, Ferrario et al (2012) used the term ''sympagic'' (=''with ice''), also proposed by Whitaker (1977).…”

“…The analysis of living cells attached to sand grains or minerals removed from submerged flanks of several icebergs gave the possibility to enhance and emend its original description (Ferrario et al 2012). Other diatoms have been sighted for the walls of free-floating Antarctic icebergs: Biddulphia aff.…”