Costal Strip Accumulation and Lorica Assembly In the Marine Choanoflagellate Diplotheca Costata Valkanov

ABSTRACT The lorica of the tectiform choanoflagellate D. costata contains five categories of costal strips distinguishable from each other on the basis of morphology and patterning. Categories of strips include those forming the anterior transverse costa; the anterior, intermediate, and posterior costal strips, respectively, of the longitudinal costae and those constituting the posterior transverse costa. the distinctive morphology of each class of strips makes it possible to observe their location and orientation within the overall accumulation of strips at the top of the parent cell collar. In Diplotheca costata the orientation and positioning of the different categories of strips in an accumulation anticipates their orientation and imbrication in the mature lorica. Assembly of the lorica from an accumulation of strips involves lateral sliding of costal strips to constitute transverse costae and longitudinal sliding of strips to constitute longitudinal costae. the motive force for lorica assembly is provided by extension of the anterolateral tentacles.     

Choanoflagellate lorica construction and assembly: the nudiform condition. I. Savillea species

The lorica of Savillea spp. (Choanoflagellida) comprises a two layered arrangement of siliceous costae, the inner layer consists of helical costae and the outer layer longitudinal. In Savillea micropora, the helical costae, in a left-handed conformation, undergo 1.5 turns and extend from a short distance above the base of the lorica to the anterior opening. In S. parva the helical costae undergo two turns from base to anterior opening. Ratios of the numbers of helical to longitudinal costae vary from 1:1 in S. parva to 1:1-1:4 in S. micropora. Cell division in Savillea is of the nudiform type, whereby a cell divides to produce a 'naked' flagellated juvenile that swims away from the parent lorica, settles on to a surface and produces a complete set of costal strips. The first formed strips are those that will form the longitudinal costae, this is followed by the slightly thicker strips which will form the inner helical costae. Lorica assembly occurs as a single continuous process and is mediated by the forward movement of the collar tentacles and a rotational movement by the cell. The longitudinal and helical costae are thereby moved in this one combined movement to their respective positions. The longitudinal costae must rotate freely during assembly whilst the helical costae are held at their front end by the respective longitudinal costae and their rear end on the surface of the cell sheath. The concluding inference, based on lorica construction, that there must be a rotational as well as the observed forward movement during lorica assembly is of seminal importance to understanding the basic pattern of lorica construction and the mechanism of lorica assembly in all choanoflagellates.     

Developmental studies on the loricate choanoflagellateStephanoeca diplocostata ellis

Summary Cells ofStephanoeca diplocostata comprise a colourless, flagellated, protoplast lodged in a lorica made of siliceous costae. The single anterior flagellum creates a water current from which bacteria and other food particles are filtered by the collar and ingested by linguiform pseudopodia that arise from the protoplast at the base of the collar. A waist divides the lorica into two chambers, the anterior of which contains three transverse and 17–20 longitudinal costae whereas the posterior chamber comprises two systems of spirally deflected costae and on some cells a pedicel at the hind end. Between 150–185 costal strips of similar length form the lorica. A thin investment covers the inner surface of the posterior chamber and lower part of the anterior chamber and joins with the protoplast at the level of the waist. Costal strips are produced within membrane-bounded vesicles in the peripheral cytoplasm and, although the origin of these vesicles is unknown, there is usually a close association with the Golgi apparatus. Once complete, strips are apparently released sideways through the plasmalemma into the cavity of the posterior lorica chamber. Later, bundles of strips are transferred to the top of the inner surface of the collar where they collectively form a horizontal ring. When sufficient strips to form a lorica have been accumulated at the top of the collar, cell division proceeds.     

Kakoeca antarctica gen. et sp.n., a loricate choanoflagellate (Acanthoecidae, Choanoflagellida) from Antarctic sea ice with a unique protoplast suspensory membrane

A new genus and species of loricate choanoflagellate, Kakoeca aniarctica Buck & Marchant gen. et sp.n. grown in rough culture from an Antarctic sea ice innoculum is described. This organism has a distinctive lorica morphology consisting of more than 200 costal strips arranged in transverse and longitudinal costae that arc perpendicular to one another in the posterior portion of the lorica. The transverse costae show declination with respect to the lorica axis in the anterior part of the lorica. The cell is suspended in the lorica by a robust protoplast suspensory membrane. This membrane blocks water flow from the posterior of the lorica necessitating water entry through the side of the lorica, an area where the maximum sized apertures in the lorica are found. Terminology (lorica lining and protoplast suspensory) is suggested for the two types of lorica membranes which have been found associated with loricas.     

Developmental studies on the loricate choanoflagellateStephanoeca diplocostata Ellis

Summary Cell division inStephanoeca diplocostata follows the accumulation of a large number of costal strips in horizontal bundles at the top of the parent collar. Prior to nuclear division the flagellum is lost and the protoplast is large and rectangular. Nuclear division takes place whilst the protoplast undergoes vigorous metabolic movements and subsequent cytokinesis is achieved by equatorial constriction. The anterior of the two daughter protoplasts is the juvenile and is inverted with respect to the sister which remains attached to the parent lorica. The two protoplasts are joined by a cytoplasmic strand that consists of two threads both of which are initially attached to the daughter protoplasts at one side of the collar. Cell separation involves elongation of the strand and after each thread has broken contact with one of the daughter cells the two threads slide over each other until the juvenile is released. The juvenile takes the accumulation of supernumerary strips as it leaves the parent lorica and after release of the juvenile the strips are mobilised to form a new lorica. The collar tentacles of the parent are thought to play a significant role in the movement of strips during division and certain selected tentacles on the juvenile are associated with lorica assembly. Cell separation takes between 9–12 minutes and lorica assembly by the juvenile 2–3 minutes.     

Role of the cytoskeleton in choanoflagellate lorica assembly

ABSTRACT. Cell division in Acanthoeca spectabilis produces a "naked" motile daughter cell (juvenile) that settles onto a surface and deposits siliceous costal strips that are stored extracellularly in bundles. When complete, the bundles of strips are assembled in a single continuous movement to form a basket-like lorica. Assembly can be divided into four overlapping stages. Stage 1 entails the left-handed rotation of strips at the anterior end while the posterior end remains stationary. Stage 2 includes the posterior protrusion of the cell to form a stalk. Stage 3 involves the anterior extension of the spines, and Stage 4 the dilation of the lorica chamber and deposition of the organic investment. Scanning electron microscopic images reveal a one-to-one association between the moving bundles of strips and the anterior ring of lorica-assembling tentacles. Treatment with microtubule inhibitors produces "dwarf" cells that lack stalks, have their spines extended, and possess collars but lack flagella. Treatment with microfilament (actin) inhibitors prevents extension of the anterior spines. These experiments demonstrate that posterior cell extension is primarily mediated by microtubules whereas extension of the spines is controlled by the actin cytoskeleton. The processes of cytoskeletal rotation and extracellular costal strip movement are compared, respectively, with rotation of nuclei in animal embryos and movement of mammalian cells over surfaces.     

Choanoflagellates (Sarcomastigophora, Protozoa) from the Coastal Waters of Taiwan and Japan. I. Three New Species

Three new acanthoecidaean species collected from the coastal waters of Taiwan and Japan are described: Acanthocorbis camarensis n. sp. resembles Acanthocorbis unguiculata in lorica morphology, but differs in having regularly arranged longitudinal and transverse costae at the anterior lorica chamber, and in lacking a nail at the apical end of anterior spine; Diaphanoeca spiralifurca n. sp. is characterized by the spiral arrangement of the costal strips in the posterior half of the lorica chamber and is closely related to Diaphanoeca grandis; Stephanoeca supracostata n. sp. is closely related to Stephanoeca elegans, but differs in having an additional transverse costa at the anterior lorica chamber.     

Developmental studies on the loricate choanoflagellateStephanoeca diplocostata Ellis VI. Effects of silica replenishment on silica impoverished cells

Summary Stephanoeca diplocostata has a facultative requirement for silica in that silica starvation does not inhibit growth as measured by increase in cell numbers. In spite of the absence of a lorica silica impoverished protoplasts still divide in the characteristic tectiform manner and a juvenile protoplast, when released from the parent cell, still extends its lorica assembling tentacles despite the absence of costal strips with which to produce a lorica. Replenishment of silica to silica starved cells in mid to late exponential phase cultures results in a decrease in the growth rate but at the same time silica is taken up and utilised for the deposition of costal strips. Mature costal strips are extruded and accumulated in bundles of 5–8 on the surface of the protoplast but are not passed to the top of the collar as would be expected in silica enriched loricate cells. Eventually silica replenished protoplasts use the bundles of costal strips to assemble loricae for themselves. In early exponential phase cultures naked protoplasts are capable of division whilst at the same time depositing costal strips in preparation for subsequent lorica assembly. An undamaged protoplast deprived of its lorica by ultrasonic treatment also ultimately replaces the lost lorica. The manner in which the tectiform mode of costal strip accumulation and lorica assembly is modified to allow a cell to produce its own lorica is discussed.Abbrevations SDV silica deposition vesicle     

Choanoflagellate lorica construction and assembly: the nudiform condition. II. Acanthoeca spectabilis Ellis

Acanthoeca spectabilis is one of the most common loricate choanoflagellates found in marine biofilms everywhere. However, it is special for two reasons; firstly, it is probably the most distinctive member of the small nudiform clade of loricate choanoflagellates. Secondly, the lorica chamber of Acanthoeca comprises a closely wound left-handed coil of costae that is unique amongst choanoflagellates. Mathematical analysis of the lorica chamber shows that the helical costae undergo two turns. This species, more than any, demonstrates that the helical coiling of costae can only be achieved by a rotational movement generated by the cell during lorica assembly. Comparison of the lorica morphology of Acanthoeca with that of the closely related genus Polyoeca indicates that the helical costae of Acanthoeca are probably homologous with the outer longitudinal costae of Polyoeca. This is unusual because helical costae are usually the innermost layer of costae. However, since there is no 'true' inner layer in the chamber of Acanthoeca the outer layer of costae are adjacent to the cell surface and therefore available for coiling. In contrast to tectiform choanoflagellates, which number more than one hundred species and inhabit a wide variety of microniches, the six known extant nudiform species must either represent a minor evolutionary development or be the remnants of a previously more extensive radiation.     

Stephanoeca arndti spec. nov. – First cultivation success including molecular and autecological data from a freshwater acanthoecid choanoflagellate from Samoa

Until recently acanthoecid choanoflagellates have been described only from marine and brackish waters. Here I describe a distinct, strictly freshwater acanthoecid species from Samoa based on its morphology, ecology and molecular biological data (partial Small Subunit rDNA). The lorica of the species is characterised by two extensions at the posterior chamber which are used for attachment to the substratum. The posterior chamber is constructed of irregularly arranged costae. The anterior chamber consists of four transverse costal rings and 14–18 longitudinal costae. Despite its sturdy appearance, the lorica was extremely sensitive to water turbulence and movements of the water. The species showed a salinity tolerance of 0.5 practical salinity units with reduced growth rates and a temperature tolerance range of 20–34 °C. According to the morphology, phylogenetic analysis, and autecology of the species it was classified as a member of the genus Stephanoeca.     

Developmental and ultrastructural observations on two stalked marine choanoflagellates, Acanthoecopsis spiculifera Norris and Acanthoeca spectabilis Ellis.

Acanthoecopsis spiculifera and Acanthoeca spectabilis are stalked, loricate choanoflagellates found in littoral sea water pools. The two taxa are distinguished from each other by the arrangement of costae forming the lorica chamber. In addition, Acanthoecopsis spiculifera usually has a longer stalk and may be colonial, consisting of two or more attached individuals. Division in Acanthoeca results in the production of a juvenile, flagellated, protoplast without a lorica. After separation, the juvenile protoplast swims away, settles down and produces an accumulation of costal strips. When sufficient strips have been produced the lorica is rapidly assembled.     

A Light and Electron Microscopical Investigation of Loricate Choanoflagellates (Choanoflagellida, Acanthoecidae) from the Andaman Sea, SW Thailand and Denmark: Species of Cosmoeca gen. n.

The choanoflagellate genus Cosmoeca gen.n. is characterized by a very regular arrangement of rod-shaped costal strips, forming 9–12 longitudinal costae (each composed of 34 costal strips) and 2–3 transverse costae. Anteriorly the longitudinal costae attach the transverse costae at the joints between neighbouring transverse costal strips. Five species of Cosmoeca are described: norvegica sp.n. (type species; previously referred to as sp. "N"), C. ventricosa sp.n., (C. phuketensis sp.n., C. subulata sp.n. and C. ceratophora sp.n. Cosmoece ventricosa sp.n. is obviously part of from complex, the extent of which has not yet been fully explained. In this paper, three groups of specimens clearly related to C. ventricosa sp.n. are illustrated and briefly described ( C. ventricosa forms A. B, C). Form A appears to be identical to Pleurasiga orculaeformis Schiller, 1925, sensu Leadbeater.     

Three-dimensional images of choanoflagellate loricae

Choanoflagellates are unicellular filter-feeding protozoa distributed universally in aquatic habitats. Cells are ovoid in shape with a single anterior flagellum encircled by a funnel-shaped collar of microvilli. Movement of the flagellum creates water currents from which food particles are entrapped on the outer surface of the collar and ingested by pseudopodia. One group of marine choanoflagellates has evolved an elaborate basket-like exoskeleton, the lorica, comprising two layers of siliceous costae made up of costal strips. A computer graphic model has been developed for generating three-dimensional images of choanoflagellate loricae based on a universal set of 'rules' derived from electron microscopical observations. This model has proved seminal in understanding how complex costal patterns can be assembled in a single continuous movement. The lorica, which provides a rigid framework around the cell, is multifunctional. It resists the locomotory forces generated by flagellar movement, directs and enhances water flow over the collar and, for planktonic species, contributes towards maintaining cells in suspension. Since the functional morphology of choanoflagellate cells is so effective and has been highly conserved within the group, the ecological and evolutionary radiation of choanoflagellates is almost entirely dependent on the ability of the external coverings, particularly the lorica, to diversify.     

Loricate choanoflagellates (Acanthoecida) from warm water seas. II. Bicosta,Apheloecion, Campyloacantha,Crucispina, Calliacantha and Saroeca

The main outcome of this and subsequent papers is to provide a baseline survey of heterotrophic protist diversity from warm water marine ecosystems, exemplified by loricate choanoflagellates (Acanthoecida). Genera in focus here (i.e. Bicosta, Apheloecion, Campyloacantha, Crucispina, Calliacantha and Saroeca) possess anterior spines or projections and a posterior pedicel, and have 0, 1 or 2 transverse costae. Longitudinal costae are, with the exception of Campyloacantha, external to transverse costal elements across all genera examined here. We describe here Apheloecion eqpacia sp. nov. and Calliacantha magna sp. nov., both of which are so far distributionally confined to warm water habitats. A ‘form A’ of Bicosta minor is introduced to facilitate the distinction between B. minor sensu stricto and a presumed warm water adapted variant with a posterior lorica chamber twist of the longitudinal costae.     

Acanthocorbis mongolica nov. spec.: description of the first freshwater loricate choanoflagellate (Acanthoecida) from a Mongolian lake

A new acanthoecid choanoflagellate species, Acanthocorbis mongolica sp. nov. was found in preserved phytoplankton samples from the freshwater lake Bayan Nuur (Uvs Nuur Basin, NW Mongolia) in concentrations of up to 1.8×10(5)cellsL(-1). It is the first well-documented species of the mainly marine order Acanthoecida to be found in a freshwater lake. The lorica structures were studied with scanning electron microscopy. Key morphological features of the vase-shaped lorica are spine bases that are composed of multiple (2-4) parallel costal strips, and the existence of two transverse costae. The ecological implications of this find are discussed.     

Some critical qualitative details of lorica construction in the type species of Calliacantha Leadbeater (Choanoflagellata).

Qualitative structural details, amplifying or correcting previous accounts in the literature on this species have been compiled by means of light and/or electron microscopy of dry whole mounts, prepared in situ from freshly gathered wild material mainly from temperate sources in Denmark, Britain and south Alaska. The more important findings are summarized diagrammatically. These include elaborate and constant details of assembly at the anterior end of the lorica, combined with much greater variability at the hind end. The absence of continuity between the three anterior spines and any of the six longitudinal costae present at the front end of the lorica chamber is confirmed, but a range of conditions involving numerical reduction in costal numbers at the hind end is illustrated. The overall size range encountered in the three temperate localities listed is illustrated photographically, but the large cells characteristic of arctic sources are represented, for a qualitative purpose only, by means of a single photograph recording a specimen collected beneath sea ice in N. Alaska, a source which will be considered more fully on a later occasion.     

Ultrastructural observations on marine choanoflagellates (Choano-flagellida, Acanthoecidae) from the coast of Thailand: species of Apheloecion gen.nov

Three species of loricate choanoflagellates (Choanoflagdlida,Acanthoecidae), collected from the Andaman Sea near Phuket Island(SW Thailand), have been described and referred to Apheloeciongen.nov. (holotype: A. quadrispinum sp.nov.). All species possessa single-chambered lorica composed of one transverse costs overlaidby a limited number of longitudinal costae which converge posteriorly.Anteriorly the longitudinal costae protrude above the transversecosta as sharp pointed spines. In A. quadrispinum sp.nov. andA. pentacanthum sp.nov. the lorica is terminated by a shortposterior spine, whereas in A. articulatum sp.nov. the pedicelis much more prominent, consisting of several costal stripswhich are joined end-to-end. The species of Apheloecion appearto be most closely related to species of Calliacantha and Monocosta.None of the species described are so far known from localitiesoutside the Andaman Sea.     

A new choanoflagellate species from Taiwan: morphological and molecular biological studies of Diplotheca elongata nov. spec. and D. costata

A new species of acanthoecid choanoflagellate isolated from brackish waters of the Danshui estuary in North Taiwan has a mineralized lorica that consists of two chambers with a total length of 19-36microm. It shares with Diplotheca costata the features of a posterior lorica chamber formed from broad and flattened costal strips and an anterior chamber with spatula-shaped costal strips. The new species has therefore been placed in the same genus and named Diplotheca elongata. A phylogenetic analysis of partial SSU rDNA sequences from Diplotheca costata and D. elongata supports this taxonomic affiliation. This is a large and distinctive choanoflagellate which has not been reported in any previous study, suggesting that it may be an endemic species of restricted distribution.     

Developmental studies on the loricate choanoflagellateStephanoeca diplocostata Ellis. V. The cytoskeleton and the effects of microtubule poisons

Summary InStephanoeca diplocostata microtubules are located in four positions namely: within the flagellar axoneme; just beneath the plasmalemma; associated with the silica deposition vesicles (SDVs) during early stages of costal strip deposition; and in the mitotic spindle. At the anterior end of the cell the 50–60 peripheral microtubules, which are organized more or less parallel to the long axis of the cell, converge around the base of the emergent flagellum. A short second flagellar base is positioned between the nucleus and the base of the emergent flagellum. Developing costal strips are located individually within SDVs in the peripheral cytoplasm. During the early stages of silica deposition each SDV is curved and subtended longitudinally on its concave side by two microtubules. When a costal strip has achieved sufficient rigidity to withstand bending the SDV-associated microtubules are depolymerized. Treatment of exponentially growing cells with sublethal concentrations of microtubule poisons, such as colchicine, podophyllotoxin, griseofulvin andVinca alkaloids depresses growth. Treatment with these drugs also affects the length and morphology of developing costal strips perhaps by interfering with the shaping and supporting functions of SDV-associated microtubules. Instead of being long and crescentic with a standard radius of curvature, costal strips of treated cells are usually short and misshapen, with irregular bends. After drug treatment, juveniles produced as a result of cell division do not develop flagella but can still assemble a lorica although it is usually misshapen. The role of microtubules and microfilaments in lorica production is discussed.