Uncovering hidden structures: previously undescribed pseudopodia and ectoplasmic structures in planktonic foraminifera

Abstract

The trophic strategies of cold-water planktonic foraminifera are not well understood due to the challenge of culturing them in polar conditions. Here, we identify previously unknown ectoplasmic and cytoplasmic projections in three species of planktonic foraminifera thriving in polar and subpolar marine environments: Globigerina bulloides, Neogloboquadrina incompta and Neogloboquadrina pachyderma. These structures were observed during routine monitoring of cultured specimens sampled from the Norwegian coast, Greenland Sea and Baffin Bay. Two types of projections were discovered, including permanent and non-permanent structures such as ectoplasmic roots, twigs and twig-like projections, similar to those observed in benthic taxa Cibicides and Cibicidoides. Additionally, a previously undescribed filopodia-like projection was observed in N. pachyderma. We discuss the function, the ecological significance and the potential impact on pelagic processes of the presence of these structures in foraminifera species that occupy diverse niches in the water column. Our findings suggest that these structures may play an important role in the trophic strategies of cold-water planktonic foraminifera, and further research and observations are necessary to fully comprehend their significance in the carbon cycle.

Large-scale culturing of the subpolar foraminifera Globigerina bulloides reveals tolerance to a large range of environmental parameters associated to different life-strategies and an extended lifespan

“…Their onset was first noted on day 16 with small particles being retained on the spines/rhizopods (seen in inset). Over the following months they developed into twig-like permanent structures This specimen is also shown in Greco et al. (2023) , labeled GcLow_18.…”

“…Ectoplasmic structures, or twigs as described by Greco et al. (2023) , were first noted as the aggregation of food particles along the rhizopods and spines of specimen CI77_18 on day 16 ( Fig.…”

“…The implication of different feeding regimes on cultured specimens has not been investigated despite it likely having a large role to play in a specimen’s adaptation to life in culture and subsequent tolerance to different environmental parameters. Recent findings of previously undescribed behaviors, such as ectoplasmic structures ( Greco et al., 2023 ) further underscore the necessity for comprehensive reportage of G. bulloides behaviour in culture.…”

Continuous reproduction of planktonic foraminifera in laboratory culture

“…The observation of such a high number of events for N. pachyderma allowed us to image specimens before and after their reproductive event (Figure 4). Before the event, the specimens present a bright red cytoplasm occupying most chambers of the calcite shell despite a large rhizopodial network, sometimes displaying long ectoplasmic structures (Greco et al, 2023; Figure 4). Specimens were observed to feed in large quantities (Greco et al, 2023; Figure 2) until very shortly before the reproductive event.…”

“…Before the event, the specimens present a bright red cytoplasm occupying most chambers of the calcite shell despite a large rhizopodial network, sometimes displaying long ectoplasmic structures (Greco et al, 2023; Figure 4). Specimens were observed to feed in large quantities (Greco et al, 2023; Figure 2) until very shortly before the reproductive event. They all bear the morphological traits identified during previous culture work and described in the method section: a very thin and translucent shell displaying almost perfect spherical chambers (Figure 4).…”