Heterotrophic flagellates and centrohelid heliozoans from marine waters of Curacao, the Netherlands Antilles
Introduction
Heterotrophic flagellates and centrohelid heliozoans are the smallest and least studied groups of protists at both the morphological and molecular levels. Heterotrophic flagellates – the collective name for an extremely diverse “hodgepodge” of polyphyletic, colorless protists moving or feeding with flagella at least in one stage of their life cycle (Patterson and Larsen 1991) – are characterized by a significant variety of metabolism and ecology. At the same time, centrohelid heliozoans (Centroplasthelida Febvre-Chevalier and Febvre, 1984) is a monophyletic group of predatory protists, related to haptophyte algae within the supergroup Haptista Cavalier-Smith, 2003 (Burki et al. 2016). Centrohelids are characterized by the presence of surface cytoskeletal structures – siliceous scales or organic spicules, having an important diagnostic value. Heterotrophic flagellates and heliozoans are widespread in different types of freshwater and marine biotopes and play an important role in the functioning of the microbial food webs, thus providing effective pathways for the transformation of matter and energy in aquatic ecosystems (Arndt et al. 2000; Domaizon et al. 2003; Kiss et al. 2009).
Faunistic investigations of heterotrophic flagellates and heliozoans supported with morphological descriptions were especially common in protistological literature in the 90 s – early 2000s (Larsen and Patterson 1990; Lee and Patterson 2000; Lee et al. 2003; Mikrjukov 2001; Patterson and Simpson 1996; Patterson et al. 1993; Tong 1997b, c; Vørs 1992). At present, such studies are relatively rare and have been largely replaced by molecular surveys from bulk microbial community DNA (Geisen et al., 2019; Pawlowski et al., 2016). However, several recent advances in the study of eukaryotic evolution have been specifically tied to morphological identification of flagellates and heliozoans in natural samples, their isolation into culture, and genomic and ultrastructural investigations of such cultures. Morphological recognition and identification (sometimes approximate) of these protists in samples is precisely based on such “classical” studies, and would not have been possible without these. For example, recent recognition, isolation, and investigation of previously understudied or unknown heterotrophic flagellates was essential in addressing major evolutionary problems, such as the origins of photosynthesis and parasitism and the trajectory of plastid spread (Gawryluk et al. 2019; Janouškovec et al. 2015; Tikhonenkov et al. 2020b), the origin of multicellular animals (Hehenberger et al. 2017; Tikhonenkov et al. 2020a), the evolution of mitochondrial genomes, and the rooting of the tree of eukaryotes and clarification of their relationships (Janouškovec et al. 2017; Lax et al. 2018; Strassert et al. 2019). Identification and establishing of clonal cultures of centrohelids was crucial for transcriptomic research and untangling the early diversification of eukaryotes (Burki et al. 2016).
Descriptions of many flagellates and heliozoans were made in the late XIX and early XX centuries using imperfect light microscopy. Many of these species lack type material, ultrastructural, and molecular data, and the taxonomy of many species and groups is in need of revision (Lee et al. 2003; Schoenle et al. 2020). Currently, the described diversity of these protists represents only a small fraction of their total species richness in nature (Cavalier-Smith and von der Heyden 2007; Corliss 2002). Metagenomic and metabarcoding sequencing of environmental samples has revealed several lineages representing high levels of hidden diversity: e.g., ribogroups MALV, MAST, MAOP, MAFO, deep‐sea pelagic diplonemids (DSPD), or eupelagonemids (del Campo and Ruiz-Trillo, 2013; del Campo et al., 2015; Guillou et al. 2008; Massana and Pedrós-Alió 2008; Okamoto et al. 2019; de Vargas et al., 2015), as well as a great variety of small new phylogenetic lineages associated with almost all large eukaryotic groups (del Campo et al., 2016; Keeling and Campo, 2017). New species of flagellates and centrohelids are being discovered constantly, which is indicative of a poor state of exploration and insufficient sampling.
At the same time, the issues of the geographical distribution of protists are subject to lively, but stubbornly unresolved debate (Azovsky et al. 2016). Are protists species widespread around the globe, or is their distribution, like those of macroorganisms, more governed by the rules of historical biogeography? There are two alternative points of view on this issue: the Ubiquity Model (Fenchel and Finlay 2004; Finlay et al. 1996) and Moderate Endemicity Model (Foissner 2004, 2008). Additional data are needed to resolve this issue, especially in those regions on the planet that remain unexplored.
Here we describe a microscopical investigation of the species diversity of heterotrophic flagellates and centrohelid heliozoans in marine waters of the coast of Curacao, which has not specifically been investigated previously. Only one species (Choanoeca flexa Brunet et al., 2019) was described from the coastal waters of Curacao (Brunet et al. 2019). Thirty six species of heterotrophic flagellates and one centrohelid heliozoan (Heterophrys myriopoda Archer, 1869) are known from the Caribbean Sea in general (Thomsen and Østergaard 2019; Thomsen et al. 2020; Vørs, 1993b) until recently. We find the diversity of heterotrophic protists on Curacao to be rich and intriguing, including the presence of species potentially important for clarifying previously puzzling evolutionary and ecological questions. We describe a survey of light and electron microscopical studies of the diversity of heterotrophic flagellates and centrohelid heliozoans from marine waters of several locations on Curacao, and provide micrographs and morphological descriptions of observed species, as well as discussing their distribution and potential importance.
Section snippets
Material and methods
Marine water samples were taken from eight locations around the island of Curacao in April 2018. Samples came from several biotopes (from the surface of corals and sponges, Sargassum algae wrings, sand, coral sand, and water column) both nearshore and at depths of 12–25 m (detailed descriptions of sampling points are given in Table 1). From each biotope, several replicates were taken, which were subsequently summarized. A total of 52 samples were investigated microscopically. Water temperature
Results
Eighty-six species and forms of heterotrophic flagellates and three species of centrohelid heliozoans were observed (Table 2) and listed systematically according to the system of eukaryotes by Adl et al. (2019). This system operates hierarchical nameless ranks that ignore endings of clade names. Thus, genera grouped into a clade represent a family (Adl et al., 2019). A system of asterisks was used to identify levels of taxonomic ranks from high to low (the more asterisks, the lower the rank of
Discussion
The morphology of many of the observed species was slightly different from previous descriptions of any protist. Seven flagellate species were identified only to genus level: Thecamonas sp., Colpodella sp., Cyranomonas sp., Goniomonas sp., Petalomonas sp., Ploeotia sp. 1, and Ploeotia sp. 2. These organisms may represent not yet described species of these genera, but further studies are needed. Among the 86 heterotrophic flagellates and 3 centrohelids encountered in this survey (Table 2), five
Author contributions
Light and electron microscopy, species identification, preparation of species descriptions and illustrations, writing of the original draft (KIP, DVT); statistical analysis (DVT); fieldwork and supervision (DVT, PJK); funding acquisition (DVT, PJK); manuscript review and editing (PJK).
Acknowledgments
This work was supported by grant from the Russian Foundation for Basic Research (grant no. 20-34-70049) and carried out within the framework of the project no. АААА-А18-118012690098-5 of the Ministry of Education and Science of the Russian Federation. We thank The Gordon and Betty Moore Foundation for travel support, Mark Vermeij and CARMABI research station for field sampling support, Emma George for help with sample collection, and the anonymous reviewers for their careful reading of our
References (153)
- et al.
An estimation of the global diversity and distribution of smallest eukaryotes: biogeography of marine benthic heterotrophic flagellates
Protist.
(2016) - et al.
Observations on Petalomonas cantuscygni, n. sp., a new halo-tolerant strain
Arch. Protistenk.
(1986) - et al.
Phylogeny and evolution of Apusomonadida (Protozoa: Apusozoa): new genera and species
Protist.
(2010) - et al.
Molecular phylogeny, scale evolution and taxonomy of Centrohelid Heliozoan
Mol. Phylogenet. Evol.
(2007) - et al.
Ultrastructure, life cycle and molecular phylogenetic position of a novel marine sand-dwelling cercozoan: Clautriavia biflagellata n. sp
Protist.
(2010) - et al.
Ecological and evolutionary significance of novel protist lineages
Eur. J. Protistol.
(2016) - et al.
Taxon-specific and seasonal variations in flagellates grazing on heterotrophic bacteria in the oligotrophic Lake Annecy – importance of mixotrophy
FEMS Microbiol. Ecol.
(2003) Electron microscopic observations on scales of species of the genus Acanthocystis (Centrohelidia, Heliozoa) from Chile
I. Arch. Protistenk.
(1985)An electron microscopical study of freshwater Heliozoa (genus Acanthocystis, Centrohelidia) from Chile, New Zealand, Malaysia and Sri Lanka. II. Arch
Protistenk.
(1987)- et al.
The novel marine gliding zooflagellate genus Mantamonas (Mantamonadida ord.n.: Apusozoa)
Protist
(2011)
Novel cultured protists identity deep-branching environmental DNA clades of Cercozoa: new genera Tremula, Micrometopion, Minimassisteria, Budifila, Peregrinia
Protist
Phylogenomics supports the monophyly of the Cercozoa
Mol. Phylogenet. Evol.
Colponemids represent multiple ancient alveolate lineages
Curr. Biol.
Marine protists are not just big bacteria
Curr. Biol.
Structure and seasonal dynamics of the protozoan community (heterotrophic flagellates, ciliates, amoeboid protozoa) in the plankton of a large river (River Danube, Hungary)
Eur. J. Protistol.
Strains of the heterotrophic flagellate Bodo designis from different environments vary considerably with respect to salinity preference and SSU rRNAgene composition
Protist.
Choanoflagellate lorica construction and as-sembly: the nudiform condition. II. Acanthoeca spectabilis Ellis
Protist.
Unveiling new microbial eukaryotes in the surface ocean
Curr. Opin. Microbiol.
Microscopical atudies on Ministeria vibrans Tong, 1997 (Filasterea) highlight the cytoskeletal structure of the common ancestor of Filasterea, Metazoa and Choanoflagellata
Protist.
Comparison of similar Arctic and Antarctic morphotypes of heterotrophic protists regarding their genotypes and ecotypes
Protist.
Heterotrophic flagellates from coastal marine and hypersaline sediments in Western Australia
Eur. J. Protistol.
Protist metabarcoding and environmental biomonitoring: time for change
Eur. J. Protistol.
Revisions to the classification, nomenclature, and diversity of eukaryotes
J. Eukaryot. Microbiol.
Flagellates from stromatolites and surrounding sediments in Shark Bay, Western Australia
Acta Protozool.
Functional diversity of heterotrophic flagellates in aquatic ecosystems
Free-living heterotrophic flagellates from intertidal sediments of Saros Bay, Aegean Sea (Turkey)
Acta Protozool.
Does size really matter in biogeography? Patterns and drivers of global distribution of marine micro- and meiofauna
J. Biogeogr.
DNA evidence for global dispersal and probableendemicity of protozoa
BMC Evol. Biol.
Rhizarian ‘novel clade 10’ revealed as abundant and diverse planktonic and terrestrial flagellates, including Aquavolon n. gen
J. Eukaryot. Microbiol.
Nanoflagellates from coastal waters of Southern Brazil
Bot. Mar.
Light-regulated collective contractility in a multicellular choanoflagellate
Science.
Untangling the early diversification of eukaryotes: a phylogenomic study of the evolutionary origins of Centrohelida, Haptophyta and Cryptista
Proc. R. Soc. B: Biol. Sci.
Biodiversity and biocomplexity of the protists and an overview of their significant roles in maintenance of our biosphere
Acta Protozool.
Observations of the heliozoean genera Pinaciophora and Acanthocystis (Heliozoea, Sarcodina, Protozoa) from Ellis Fjord, Antarctica
Polar Biol.
Environmental survey meta-analysis reveals hidden diversity among unicellular Opisthokonts
Mol. Biol. Evol.
Diversity and distribution of unicellular Opisthokonts along the European coast analyzed using high-throughput sequencing
Environ. Microbiol.
Heterotrophic flagellates from coral reef sediments (Great Barier Reef, Australia)
Arch. Protistenk.
“Protist X” Is a Predatory Anaerobe That Represents a Novel Deep Lineage of Eukaryotes. Abstracts of the 5th Joint Meeting of PSA / ISOP, July 29–Aug. 2, 2018
Meteora sporadica represents a new major lineage of eukaryotes
Book of Abstracts of 15th International Congress of Protistology, 30th July – 4th August 2017, Prague, Czech Republic. 2017
Die Flagellaten Der Kochsalzteiche zu torda und szamosfalva
Természetrajzi Fuzetek.
Ecology of Centrohelid Heliozoa in the Southern Urals reservoirs
Bull. Orenburg State Univ.
The ubiquity of small species: patterns of local and global diversity
Bioscience.
The diversity of microbes: resur-gence of the phenotype
Philos. Trans. Biol. Sci.
Biodiversity at the microbial level: the number of free-living ciliates in the biosphere
Q. Rev. Biol.
Ubiquity and cosmopolitanism of protists questioned
SIL News.
Protist diversity and distribution: some basic considerations
Biodivers. Conserv.
Der Organismus Der Craspedomonaden
Single-cell transcriptomics using spliced leader PCR: evidence for multiple losses of photosynthesis in polykrikoid dinoflagellates
BMC Genomics
Non-photosynthetic predators are sister to red algae
Nature.
A user guide to environmental protistology: primers, metabarcoding, sequencing, and analyses
BioRxiv
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2022, European Journal of ProtistologyCitation Excerpt :Morphological descriptions of species and taxonomic diagnoses of new centrohelids Acanthocystis tyrasiana sp. nov., Pterocystis borysthenica sp. nov., and Khitsovia mutabilis gen. et sp. nov. are listed below. Information on the distribution of the observed species is provided in Supplementary Table S1. DIAPHORETICKES Adl et al., 2012.