Description of Armaparvus languidus n. gen. n. sp. Confirms Ultrastructural Unity of Cutosea (Amoebozoa, Evosea)

Abstract

The American Type Culture Collection (ATCC) PRA-29 isolate has a publicly available transcriptome, which has led to its inclusion in recent phylogenomic analyses. The ATCC PRA-29 isolate was originally identified and deposited as "Pessonella sp." This taxon branches robustly within the recently discovered clade Cutosea, very distantly related to the clade in which the genus Pessonella is believed to branch based on morphological data. Using detailed light and electron microscopy, we studied the morphology and ultrastructure of ATCC PRA-29 as well as other cutosean amoebae to better elucidate the morphological affinity of ATCC PRA-29 to other amoebozoans. Here, we show that ATCC PRA-29 was misidentified by the original depositor as Pessonella and name it Armaparvus languidus n. gen. n. sp. We show that a cell coat of microscales separated from the cell membrane is a unique trait found in all known cutosean amoebae. As Cutosea represents a clade at the deepest bifurcation in the amoebozoan group Evosea and because this clade is currently taxon-poor, but likely represents a major understudied group it will be important to isolate and describe more cutosean amoebae in the future.

The amoebae of Idionectes vortex (Cutosea, Amoebozoa): Motility, cytoskeleton architecture and extracellular scales

“…This indicates that the extracellular envelope is flexible and dynamic and has the ability to transiently open for pseudopodial protrusions and attachment zones. Similar scaly cell coats have been documented for the other members of the Cutosea and are considered a common and characteristic trait of this amoebozoan lineage (discussed in Cavalier-Smith et al, 2016;Schuler & Brown, 2019). The different cutosean species show some variation in scale ultrastructure (shape, size, and appendages), but the overall morphology, arrangement, and topology of the scales in these amoebae are rather uniform, including those of I. vortex (Figure 4E).…”

“…1d in Hess et al, 2019 and fig. 3B, D, F in Schuler & Brown, 2019) and deserves some future analyses.…”

“…The different cutosean species show some variation in scale ultrastructure (shape, size, and appendages), but the overall morphology, arrangement, and topology of the scales in these amoebae are rather uniform, including those of I. vortex (Figure 4E). All known cutosean cell coats show a marked distance to the plasma membrane and lack visible attachment structures in ultrathin sections (Hess et al, 2019;Kudryavtsev & Pawlowski, 2013;Lahr et al, 2015;Schuler & Brown, 2019), raising some questions about how these coats move and reassemble during amoeboid locomotion. Yet, results from scanning electron microcopy suggest that there might be amorphous material between the scales, potentially an matrix that is not well preserved or easily contrasted during the preparation for transmission electron microscopy (only in Sq.…”

“…Despite the fact that the Cutosea represent a relatively deep branch in the amoebozoan phylogeny, this group is still poorly sampled and understood from the point of the cellular organization (Schuler & Brown, 2019). The discovery of I. vortex , a parasitoid freshwater cutosean with a flagellate life history stage and an exceptional mode of flagellar motility, raises some questions concerning the evolution of cellular traits in the Cutosea.…”

“…The discovery of the parasitoid amoeboflagellate Idionectes vortex revealed that flagellate cells are also present in the Cutosea (Hess et al, 2019). Based on our current knowledge, Idionectes represents the deepest-branching member of that group and deviates strongly from the other known cutoseans, which are relatively small (< 10 µm), bacterivorous, marine amoebae without any known flagellar stages (Kudryavtsev & Pawlowski, 2013;Lahr et al, 2015;Schuler & Brown, 2019). Idionectes is a freshwater amoeboflagellate with a complex life history comprising flagellate swarmers and trophic amoebae.…”