A new marine prasinophyte genus alternates between a flagellate and a dominant benthic stage with microrhizoids for adhesion

Prasinophytes (Chlorophyta) are a diverse, paraphyletic group of planktonic microalgae for which benthic species are largely unknown. Here, we report a sand‐dwelling, marine prasinophyte with several novel features observed in clonal cultures established from numerous locations around Australia. The new genus and species, which we name Microrhizoidea pickettheapsiorum (Mamiellophyceae), alternates between a benthic palmelloid colony, where cell division occurs, and a planktonic flagellate. Flagellates are short lived, settle and quickly resorb their flagella, the basal bodies then nucleate novel tubular appendages, termed “microrhizoids”, that lack an axoneme and function to anchor benthic cells to the substratum. To our knowledge, microrhizoids have not been observed in any other green alga or protist, are slightly smaller in diameter than flagella, generally contain nine microtubules, are long (3–5 times the length of flagella) and are not encased in scales. Following settlement, cell divisions result in a loose, palmelloid colony, each cell connected to the substratum by two microrhizoids. Flagellates are round to bean‐shaped with two long, slightly uneven flagella. Both benthic cells and flagellates, along with their flagella, are encased in thin scales. Phylogenies based on the complete chloroplast genome of Microrhizoidea show that it is clearly a member of the Mamiellophyceae, most closely related to Dolichomastix tenuilepsis. More taxon‐rich phylogenetic analyses of the 18S rRNA gene, including metabarcodes from the Tara Oceans and Ocean Sampling Day projects, confidently show the distinctive nature of Microrhizoidea, and that the described biodiversity of the Mamiellophyceae is a fraction of its real biodiversity. The discovery of a largely benthic prasinophyte changes our perspective on this group of algae and, along with the observation of other potential benthic lineages in environmental sequences, illustrates that benthic habitats can be a rich ground for algal biodiscovery.     

Search for Clues to the Evolutionary Meaning of Ciliate Phylogeny*†

SYNOPSIS. Progress in ciliatology and in allied fields may demystify ciliate phylogenetics. Concentration on hymenostomes (mainly Tetrahymena and Paramecium) may have obscured directional features of ciliate physiology in phylogenetic problems. Therefore, means are suggested for “domesticating” the presumptively primitive, predominantly marine, sand-dwelling gymnostomes having nondividing diploid macronuclei. The prize quarry is the marine psammophile Stephanopogon whose homokaryotic condition may mark it as a living fossil. Eventual axenic cultivation of these “primitive” ciliates may be aided by use as food of easily grown photosynthetic prokaryotes, some isolated from the marine sulfuretum or adjacent aerobic muds and sands where “karyorelictid” ciliates flourish. We assume that: (a) the macronucleus evolved as a coordinator of chemical and physical signals, for efficient detection of food and toxins; (b) oral structures evolved meanwhile as sensors as well as mechanical food-gatherers. This conjunction enabled complexity of adaptive behavior and evolutionary success. Ciliate origins cannot be considered apart from origin(s) of phagotrophy and its underlying versatile heterotrophy. Because of the well developed heterotrophy in some photosynthetic prokaryotes (including several proposed as food organisms), they are viewed as alternatives to blue-green algae as forebears of eukaryotes. Nor can ciliate origins be considered apart from origin(s) of eukaryotes. A check of these assumptions—that Stephanopogon and gymnostomes with nondividing macronuclei are primitive—may be forthcoming from sequencing amino acids in certain key enzymes, given an adequate sampling of ciliates, flagellates (especially dinoflagellates and cryptomonads), lower fungi, and photosynthetic prokaryotes other than blue-green algae.     

Antennal sensory organs in the millipede Eurypauropus ornatus: Fine structure of the flagella and globulus

On the antennal tip of Eurypauropus ornatus are 3 threadlike sensilla—the flagella, and a single spheroid sensillum—the globulus. Each of the 3 flagella is innervated by 2 groups of sensory cells. One group contains 4 cells, the other, 5. All cells of the “four group” and 3 of the “five group” are comprised of single cilia and unbranched dendrites which extend along the lumen of the flagellum. Two cells of the “five group” have double cilia and pairs of unbranched dendrites. One pair also enters the flagellum and the other pair terminates beneath the flagellar base to form a concentric array of lamellae. No pores are present in the cuticular wall. Eight sensory cells innervate the globulus. They are arranged in 3 groups, one triplet and 2 pairs, in addition to a single cell. The single cell contains a pair of cilia whose unbranched dendrites differentiate into tubular bodies that are inserted into the base of the globulus. Each of the other 7 sensory cells has a single cilium. Their unbranched dendrites penetrate into the globulus in 3 groups as described for the sensory cells. The dendrites in each group terminate in an individual pore channel at the globulus tip and completely fuse with the electron-dense material that plugs the pore channel. Based on structural similarities to sensilla having known functions, it is probable that the flagella and the globulus are chemoreceptors, the former responding to odors, the latter sensitive to substances in aqueous solution.     

REVIEW: Is the “flagellate” pattern of spermatogenesis plesiomorphic in Metazoa?

Summary

The phenomenon of “flagellate spermatogenesis” typically known among marine invertebrates with “primitive” sperm and external or external-internal fertilization is discussed. It is suggested that “flagella bearing” in early germinative cells might be explained by plesiomorphic similarity between these cells and flagellate somatic epithelial cells. The early germ cells of more apomorphic multicellular animals using internal fertilization with “modified” and “aberrant” sperm typically have no flagella and this organelle, as the sperm tail, first appears in spermatids. It is speculated that the “flagellate” pattern typifies the basal level and that the transition between “flagellate” and “specialized” spermatogenesis constitutes a significant step in evolution.     

Spatial and numerical regulation of flagellar biosynthesis in polarly flagellated bacteria

Control of surface organelle number and placement is a crucial aspect of the cell biology of many Gram‐positive and Gram‐negative bacteria, yet mechanistic insights into how bacteria spatially and numerically organize organelles are lacking. Many surface structures and internal complexes are spatially restricted in the bacterial cell (e.g. type IV pili, holdfasts, chemoreceptors), but perhaps none show so many distinct patterns in terms of number and localization as the flagellum. In this review, we discuss two proteins, FlhF and FlhG (also annotated FleN/YlxH), which control aspects of flagellar assembly, placement and number in polar flagellates, and may influence flagellation in some bacteria that produce peritrichous flagella. Experimental data obtained in a number of bacterial species suggest that these proteins may have acquired distinct attributes influencing flagellar assembly that reflect the diversity of flagellation patterns seen in different polar flagellates. Recent findings also suggest FlhF and FlhG are involved in other processes, such as influencing the rotation of flagella and proper cell division. Continued examination of these proteins in polar flagellates is expected to reveal how different bacteria have adapted FlhF or FlhG with specific activities to tailor flagellar biosynthesis and motility to fit the needs of each species.     

Paraphyly,ancestors, and the goals of taxonomy: A botanical defense of cladism

Cronquist (1987) criticizes cladism for its rejection of paraphyletic groups, which he would retain if he feels they are “conceptually useful.” We argue that paraphyletic higher taxa are artificial classes created by taxonomists who wish to emphasize particular characters or phenetic “gaps,” and that formal recognition of such taxa conveys a misleading picture of common ancestry and character evolution. In our view, classifications should accurately reflect the nested hierarchy of monophyletic groups that is the natural outcome of the evolutionary process. Such systems facilitate the study of evolution and provide an efficient summary of character distributions. Paraphyletic groups, such as “prokaryotes,” “green algae,” “bryophytes,” and “gymnosperms,” should be abandoned, as continued recognition of such groups will only serve to retard progress in understanding evolution. Contrary to Cronquist’s (1987) assertions, cladistic theory is not at odds with standard views on speciation and the existence of ancestors. Groups of interbreeding organisms can continue to exist after giving rise to descendant species, and there are several ways in which such groups, whether extant or extinct, can be incorporated into cladistic classification. In contrast, paraphyletic higher taxa are neither cohesive (integrated by gene flow) nor whole, do not serve as ancestors, and are unacceptable in the phylogenetic system. Fossils may be of great value in assessing phylogenetic relationships and are readily accommodated in cladistic classification. Cladistic studies are helping to answer major questions about plant evolution, and we anticipate increased efforts to develop a truly phylogenetic system.     

Ultrastructure of the scale-covered zoospores of the green alga Chaetosphaeridium, a possible ancestor of the higher plants and bryophytes

The zoospores of the green alga Chaetosphaeridium globosum are covered on all surfaces with tiny diamond-shaped scales similar to those of the prasinophycean flagellates and the Charales. The flagella also bear striated hairs (hair scales) so far considered to be a characteristic of the Prasinophyceae. The flagellar apparatus differs from that observed in the Prasinophyceae, shows many similarities to that of the Charales, and is identical with the "Vierergruppe" of the pteridophytes, cycads and bryophytes.
The zoospores are opisthokont, with two flagella inserted subapically. There is a lateral chloroplast containing typical grana and intergranal lamellae, but no eyespot. The very complicated Golgi body/contractile vacuole system comprises 10–20 contractile vacuoles. A microbody occupies a characteristic position in the cell, and in a young germling contains a crystalline inclusion.
The ultrastructure of the zoospore supports the old theory that the ancestors of the higher plants may well be found among Coleochaete and its relatives, past and present.     

Pirsonia guinardiae,gen. et spec. nov.: A parasitic flagellate on the marine diatomGuinardia flaccida with an unusual mode of food uptake

Pirsonia guinardiae gen. et spec. nov. was discovered as a parasite onGuinardia flaccida in the North Sea near List/Sylt during a bloom of this centric planktonic diatom. It is a colourless, small flagellate with an oblique cell apex and two subapically inserting flagella of different length and different orientation. The flagellates attach to a host cell and form an antapical process which pierces the diatom frustule and develops inside into a “trophosome”, consisting of a proximal digestion vacuole and distal pseudopodia which phagocytise host cytoplasm. The main body, the “auxosome”, remains outside the host cell. The trophosome persists for some time after the detachment of the auxosome or its derivatives. There are two types ofPirsonia guinardiae. Type A attaches to the valvae as well as to the girdle region, the auxosome remains flagellated and generally detaches after the feeding process to divide twice (seldom 3 times). Thick-walled (resting?) cysts are formed. Occasionally, a fusion of two sister cells has been observed. Type B attaches only to the valvae; the auxosome lacks flagella; it divides during the feeding process to give rise to a bouquet of 8 to more than 50 daughter cells which become flagellated when they detach. The taxonomical position of the flagellate is discussed. Diagnoses of genus and species are given.     

Ultrastructure and identification of the predatory flagellateColpodella pugnax Cienkowski (Apicomplexa) with a description ofColpodella turpis n. sp. and a review of the genus

A flagellated predator of the chlorophyte algaDunaliella spp. was examined by light and electron microscopy. Although this predator had previously been identified as a species of the kinetoplastid genusBodo, the present study revealed the flagellate to be indistinguishable fromColpodella pugnax, the type-species for its genus. The flagellate lacks a kinetoplast, a microtubule supported cytopharynx and paraxial rods in the flagella — characters universally found in kinetoplastid flagellates. The cell has mitochondria with vesicular cristae. Multiple membranes surround the cell and are underlain by longitudinal microtubules not originating from the flagellar region. Most notably, the flagellate has micropores and an apical complex including a conoid, sacculate rhoptries and, apparently, a polar ring. This study hs confirmed thatColpodella is the genus with free-living species most closely related to the apicomplexan parasites (i.e. the “Euapicomplexa” andPerkinsus). No unambiguous synapomorphy supports an “apicomplexan parasites” clade: Inclusion ofColpodella is necessary to secure the Apicomplexa as a monophyletic (=holophyletic) taxon. A new family, the Colpodellidae, is erected for this genus. Colpodella turpis, a previously undescribed species that also consumesDunaliella spp., was isolated from the same samples asC. pugnax. A diagnosis for this species is presented together with a brief review of the genus, in which we recognise seven species. The generic namesAlphamonas Aléxéieff,Nephromonas Droop andDingensia Patterson & Zölffel are rendered into synonomy withColpodella.     

Tarsiers,adapids and the integrity of Strepsirhini

Although strepsirhine primates can be described by their narial configuration, this and most other definable features are probably primitive retentions; only the development of a grooming claw of the second pedal digit and of a toothcomb (the latter of which has been lost in Daubentonia) emerge as potential apomorphies of the group. Within this assemblage lemurids, Lepilemur, the indriids, and Daubentonia can be argued to constitute a monophyletic group whose relationships cladistically are in the sequence listed; Lemuridae and Indriidae can themselves be delineated as monophyletic groups. The remaining strepsirhine primates—the cheirogaleids, galagids, and lorisids—also appear to constitute a definable clade, with the former group representing the sister taxon of the latter two families; cach family can be united on the basis of distinct synapomorphies. Although there are features—especially of the ear region—which present themselves as potentially reflective of the sister relationship of Tarsius + Anthropoidea, other characters, including the possession of the grooming claw, are suggestive of an alternative scheme: Tarsius may be the sister of the extant lorisiform group, thereby reconstituting, albeit in a novel form, the primate suborder Prosimii. It also appears that fossil “tarsioids” may in fact be more closely related to the extant lorisiforms than to Tarsius. A reconsideration of the so-called fossil lemurs, the adapids, leads to the conclusion that Adapis-like primates are a clade apart from Pelycodus, Notharctus, Smilodectes and their most immediate relatives, and may themselves constitute a clade that is related as the primitive sister to all other “prosimians” by virtue of the development of the so-called free intrabullar tympanic ring.     

Enzyme distribution in "naturally-decapitated" bull spermatozoa: acetylcholinesterase, adenylpyrophosphatase and adenosinetriphosphatase

Naturally-decapitated spermatozoa were separated into motile flagella and head and immotile flagella by differential and density gradient centrifugation. In preparations microscopically free of cross-contamination after repeated centrifugation, the heads appeared to be enzymatically inert, while there was virtually no change in the specific activity of the immotile flagella which had been subjected to as much manipulation as the heads. The non-motile flagella had almost twice the acetylcholinesterase and about one-third the apyrase activity of the motile flagella. The flagella appear to contain a structurally-bound adenosinetriphosphatase which may be identical with the “spermosin” extracted from bull sperm.     

The Mode of Attachment of Trypanosoma vivax in the Proboscis of the Tsetse Fly Glossina fuscipes: an Ultrastructural Study of the Epimastigote Stage of the Trypanosome*

SYNOPSIS. The ultrastructure of attached Trypanosoma vivax epimastigote clusters in the proboscis of the tsetse fly Glossina fuscipes is described from electron micrographs of thin sections. Some flagellates are attached directly to the lining of the insect's labrum by their flagella, most of which are aligned along the long axis of the proboscis. Other trypanosomes are attached indirectly, their flagella adhering to those of flagellates which are directly attached. Junctional complexes similar to those described from metazoan epithelia are found on the flagellar membrane. A long zonular hemidesmosome attaches the flagellum to the proboscis wall and a series of closely set macular desmosomes link the flagellar membranes of adjacent flagellates. Unlike the trypomastigote stages of T. vivax, more than one row of macular desmosomes may be present along the flagellum-body junction of the trypanosome. It is suggested that all these Junctional complexes serve to buttress the flagellate's attachment to its insect host and so maintain anchorage of the parasite during the fly's blood meals. The ability of the flagellum of trypanosomatids to form Junctional complexes may be a factor contributing to their success as parasites, this adaptation enabling them to multiply while attached to host surfaces.     

Selektion und Evolutionstheorie: Müssen »altdarwinistische Dogmen« durch eine kritische Evolutionstheorie ersetzt werden?

Some authors (mainlyBonik, Gutmann, andPeters) have tried to revise current evolutionary concepts, fraught — in their opinion — with “1paleodarwinistic dogmas”. Some points of their theories are reviewed critically in the present paper: (1) Evolution is of course inimaginable without selection, but an “internal selection” eliminating misshaped embryos has nothing to do with evolution. This is stabilizing selection which reduces genetic variation and would even block evolutionary change completely if it was perfect. When this kind of internal selection was “neglected” by earlier authors, this cannot be qualified as paleodarwinistic dogmatism being in contradiction with the premises of evolutionary theory. — (2) Energetic rationalisation of organisms is certainly an important factor in selection but not an absolute law explaining everything about evolution. There are many adaptive processes resulting in less “economic” formations; e.g. heavy armors like those of tortoises, ankylosaurs, and stegosaurs. Among others, protective functions justify a certain waste of energy. — (3) Comparing organisms with technical machines provides an interesting analogy, but again this cannot be considered as the only possible approach for evolutionary models. »Maschinenanalogie« combined with a generalized »internal selection« (i.e. with the nature of adaptive changes determined by the internal construction of organisms) leads inevitably to an underestimation of selective pressures resulting from the ecologic and biocoenotic context. The simple fact of diverging evolutionary lineages shows that the same species (“machine”) can be improved in different ways under the influence of different external factors.     

Desmosomes and hemidesmosomes in the flagellate Crithidia fasciculata

Summary The flagellum of the trypanosomatid flagellate Crithidia fasciculata expands asymmetrically as it emerges from the reservoir. Where the flagellar memhrane approaches the membrane lining the reservoir, desmosomes are found. These structures are arranged in several slightly curved lines and have many features in common with vertebrate desmosomes.In cultures, the flagellates stick to each other by their flagella and form rosettes. In these bundles of cells, probable sites of adhesion between flagella, or between flagella and pieces of debris, are marked by a dense filamentous tract which passes posteriorly along the flagellum and by a thick band lying just below the flagellar membrane. It is suggested that similar adhesions are found in the insect host where the flagellate attaches itself to the gut wall.     

Aboriginal New World epidemiology and medical care,and the impact of Old World disease imports

Various workers, including T. D. Stewart, claim that the aboriginal Americas were relatively disease-free because of the Bering Strait cold-screen, eliminating many pathogens, and the paucity of zoonotic infections because of few domestic animals. Evidence of varying validity suggests that precontact Americans had their own strains of treponemic infections, bacillary and amoebic dysenteries, influenza and viral pneumonia and other respiratory diseases, salmonellosis and perhaps other food poisoning, various arthritides, some endoparasites such as the ascarids, and several geographically circumscribed diseases such as the rickettsial verruca (Carrion's disease) and New World leishmaniasis and trypanosomiasis. Questionably aboriginal are tuberculosis and typhus. Accordingly, virtually all the “crowd-type” ecopathogenic diseases such as smallpox, yellow fever, typhoid, malaria, measles, pertussis, polio, etc., appear to have been absent from the New World, and were only brought in by White conquerors and their Black slaves. My hypothesis is that native American medical care systems—especially in the more culturally advanced areas—were sufficiently sophisticated to deal with native disease entities with reasonable competence. But native medical systems could not cope with the “crowd-type” disease imports that struck Indian and Eskimos as “virgin field” populations. Reanalysis of native population losses through a genocidal combination of disease, war, slavery and attendant cultural disruption by Dobyns, Cook and others strongly suggest that traditional estimates underplayed the death toll by a factor of the general order of ten. This would make for an immediately pre-contact Indian population of some 90–111 million instead of the traditional 8–11 million. Evidence is growing that Indians may have been no more susceptible to new pathogens than are other “virgin soil” populations, and thus their immune systems need not be considered less effective than those in other people. Present-day high mortality rates in Indians of both continents from infectious disease imports may be more socioeconomic than anything else.     

A light and electron microscopical study of the green flagellateSpermatozopsis similis spec. nova

The green flagellateSpermatozopsis similis spec. nova has been studied in culture by light and electron microscopy. The flagellate bears two flagella, is naked and has a characteristic crescent and spirally twisted cell shape. The two flagella are of subequal length, each with a prominent hair-point. Each cell contains two contractile vacuoles, a single chloroplast with an anterior eyespot but lacking a pyrenoid, an anteriorly located nucleus, a single dictyosome associated with the posterior end of the nucleus, a single mitochondrion posterior to the nucleus and associated with a small microbody, some conspicuous vacuoles, and a greater number of secondary cytoskeletal microtubules which probably are responsible for maintaining the peculiar shape of this species. SinceS. similis in culture is only biflagellate, it cannot be accommodated within the quadriflagellate, but otherwise very similar speciesS. exsultans. Spermatozopsis similis is compared with other green flagellates and is shown to share common ultrastructural characters withChlamydomonas-type green algae.     

Fine structure and taxonomic position of the giant amoeboid flagellate Pelomyxa palustris

Specimens of Pelomyxa palustris from five collecting sites had numerous nonmotile flagella. The structures are called flagella because of morphological similarities to flagella and because P. palustris has affinities with amoeboid flagellates. Flagella were photographed on living cells and studied by transmission and scanning electron microscopy. From 64 to 742 flagella per cell were estimated from scanning electron microscopy of ten cells 204 to 1269 micron in length. The nonmotile flagella arise from basal granules which were, in one strain, surrounded by radiating electron-dense microtubules. This strain also had excess axonemal microtubules. Abundant cytoplasmic microtubules were arranged in several different patterns. In about half of the P. palustris cells in which nuclei were studied, microtubules were either apposed to the nuclear membrane in a parallel alignment (with some also radiating) or radiating from the nuclear membrane (with none parallel). Bacteria associated with nuclei were of three characteristic types: Gram-negative rods, Gram-positive rods, and large rods. All nuclei within a given trophozoite had similar perinuclear features. Recent proposals for separation of Pelomyxa to its own phylum (based on its proposed primitive, unique nature) can not be justified. Pelomyxa is a complex, highly specialized organism adapted to live in a specific fresh-water environment. Mastigamoebid amoeboid flagellates of the genera Mastigamoeba, Mastigella, Mastigina, and possibly Dinamoeba are placed with Pelomyxa within the order Pelobiontida Page, 1976, emend., containing two families. Pelomyxidae Schulze, 1877, and Mastigamoebidae Goldschmidt, 1907.