Labiate Process Research Articles

Shionodiscus karianus sp. nov. (Thalassiosirales, Thalassiosiraceae), a new planktonic diatom from the Kara Sea and notes on some morphological characters of Shionodiscus taxa

The genus Shionodiscus (Thalassiosirales, Thalassiosiraceae) includes species that have strutted processes with long inward but reduced outward extensions, a labiate process typically located on the valve face, distant from the margin. Shionodiscus species inhabit the marine environment, and the genus includes both living and fossil species. In the course of our study of plankton samples from the Kara Sea, we found specimens belonging to Shionodiscus. Based on LM, SEM, and TEM investigations, a new species, Shionodiscus karianus sp. nov., is described. This species is distinguished from others in the genus based on areola densities, as well as the fine structure and location of the rimoportula and the central fultoportula and the ultrastructure of the areolae and cingulum. In this paper, we provide a morphological description of this taxon as well as a comparison with similar taxa. Previous records of Shionodiscus species in the Russian Arctic seas are discussed. Finally, we summarize and evaluate information on the important morphological characters, such as rimoportula position and fultoportula structure, for Shionodiscus.

Genome-enabled phylogenetic and functional reconstruction of an araphid pennate diatom Plagiostriata sp. CCMP470, previously assigned as a radial centric diatom, and its bacterial commensal

Diatoms are an ecologically fundamental and highly diverse group of algae, dominating marine primary production in both open-water and coastal communities. The diatoms include both centric species, which may have radial or polar symmetry, and the pennates, which include raphid and araphid species and arose within the centric lineage. Here, we use combined microscopic and molecular information to reclassify a diatom strain CCMP470, previously annotated as a radial centric species related to Leptocylindrus danicus, as an araphid pennate species in the staurosiroid lineage, within the genus Plagiostriata. CCMP470 shares key ultrastructural features with Plagiostriata taxa, such as the presence of a sternum with parallel striae, and the presence of a highly reduced labiate process on its valve; and this evolutionary position is robustly supported by multigene phylogenetic analysis. We additionally present a draft genome of CCMP470, which is the first genome available for a staurosiroid lineage. 270 Pfams (19%) found in the CCMP470 genome are not known in other diatom genomes, which otherwise does not hold big novelties compared to genomes of non-staurosiroid diatoms. Notably, our DNA library contains the genome of a bacterium within the Rhodobacterales, an alpha-proteobacterial lineage known frequently to associate with algae. We demonstrate the presence of commensal alpha-proteobacterial sequences in other published algal genome and transcriptome datasets, which may indicate widespread and persistent co-occurrence.

Fluorescent nanoplastic particles: synthesis and influence on diatoms

A method for obtaining fluorescent labeled polyvinyl chloride nanoparticles of 60-110 nm by deposition of plastic and dye solution into water has been developed. These nanoparticles are suitable for testing effect of nanoplastic on living organisms. We have cultivated diatom algae Ulnaria ferefusiformis in the presence of polyvinyl chloride nanoparticles and revealed that the suppression of the vital activity in diatoms is not due to the penetration of nanoparticles into the cell but arises from their association with the outer surface of the cells near the labiate process (rimoportula).

Shionodiscus gaarderae sp. nov. (Thalassiosirales, Thalassiosiraceae), a bloom-producing diatom from the southwestern Atlantic Ocean, and emendation of Shionodiscus bioculatus var. bioculatus

The recently established diatom genus Shionodiscus is characterized as possessing a labiate process on the valve face and strutted processes with long internal and reduced, or no, external extensions. Many Thalassiosira species with these features were transferred to this new genus, as well as some with short internal, strutted process extensions. Examination of samples from the Argentine continental shelf and slope waters, and from the Beagle Channel, revealed the presence of a small centric diatom that formed an extensive bloom in slope waters during spring 2005 and 2006. Analysis by light and electron microscopy revealed high similarity to specimens previously referred as Thalassiosira bioculata var. raripora. This name was never effectively published; nevertheless, the name has been adopted and observations referring to it have been reported on several occasions. Here we trace the usage of the (nomenclaturally invalid) name Thalassiosira bioculata var. raripora in the literature, and formally describe the species as Shionodiscus gaarderae, based on our observations and comparison with previous reports. A morphological comparison of this and similar taxa is also provided. In addition, we offer an emended description of S. bioculatus var. bioculatus from Ostenfeld material sampled from the ‘Färöer Island Naströ Fjord Plankton (16.9.1902)’, held in the Hustedt collection. Finally, we propose the transfer of Thalassiosira rosulata to Shionodiscus.

Diversity and taxonomic identification of Shionodiscus spp. in the Australian sector of the Subantarctic Zone

Diatoms are siliceous phytoplankton that play a major role in global carbon fixation, as well as forming the basis of most marine food webs. In the Southern Ocean, diatoms are responsible for significant volumes of carbon export and sequestration in the deep sea. Diatoms are unicellular and microscopic, thus diatom taxonomy has naturally progressed as imaging and molecular technologies have developed. Despite recent advancements, some aspects of diatom taxonomy remain unclear. The genus Shionodiscus was separated from Thalassiosira in 2006, and possesses, as a group, internal extensions of the marginal strutted processes as well as a labiate process on the valve face, usually distant from the margin. The features distinguishing Shionodiscus from Thalassiosira, and Shionodiscus spp. from each other, are difficult to examine under light microscopy, and most taxonomists will group similar Shionodiscus species together when encountered, rather than discriminating species. As a result, the full extent of Shionodiscus diversity is rarely examined in individual studies. In this study, sediment trap material captured in the Australian sector of the Subantarctic Zone was examined using both light and scanning electron microscopy, and compared to known measurements on Shionodiscus species and varieties. This study had two aims; to catalogue for the first time the diversity of Shionodiscus spp. within the Australian sector, and to create a formalized set of criteria for grouping Shionodiscus species, when only light microscopy analysis is possible. By documenting Shionodiscus diversity in the Australian sector and establishing a standard identification protocol, researchers will be better able to determine the ecological significance of the genus in diatom assemblages.

Fideliacyclus wombatiensis gen. et sp. nov. – a Paleocene non-marine centric diatom from northern Canada with complex frustule architecture

Marine diatoms began colonizing freshwater habitats in the early Cenozoic, or possibly earlier, becoming well established by the Eocene. However, because of a sparse fossil record, little is known about the earliest diatom representatives that signalled this important ecological and evolutionary event. We describe a new centric diatom genus, Fideliacyclus, from lake sediments deposited during the Paleocene in the Canadian Arctic. This organism, one of the oldest known freshwater diatoms reported to date, has a unique, highly complex wall structure composed of areolae with large, bulbous, spherical shaped chambers that are open to the external environment but rest on a solid siliceous surface referred to as the solum, and are surrounded by an open space, or hypocaust. The solum is only perforated by marginal labiate processes, which largely isolates the protoplast from ambient conditions hence limiting exchange; this may have represented an adaptive response to living in freshwater. Given the complement of microfossils found in the fossil locality, the lake was an unambiguously softwater, slightly acidic, limnic system of moderate nutrient content. Although the exact taxonomic position of Fideliacyclus remains uncertain, it appears to be most closely allied to Actinocyclus (Class: Coscinodiscophyceae) or possibly Spumorbis given the range of synapomorphies.

Diversity of the marine diatom Chaetoceros (Bacillariophyceae) in Thai waters – revisiting Chaetoceros compressus and Chaetoceros contortus

:Chaetoceros is one of the most species-rich phytoplankton genera, and its known diversity can be expected to increase significantly when additional material from tropical and other less studied areas has been examined by a combination of molecular and morphological methods. We have succeeded in culturing and examining a pair of very characteristic Chaetoceros species, Chaetoceros compressus and Chaetoceros contortus, from a number of geographically separate localities. The pair is easily recognizable as such because of the heavy setae characteristic of the section Compressa but morphological similarities between the two species have caused considerable taxonomic confusion since the second species, C. contortus, was described nearly one hundred years ago. Critical studies exploring species delineation are therefore needed to determine whether C. compressus and C. contortus should be considered separate species. A combination of phylogenetic analyses based on large subunit rDNA and detailed morphological studies using light microscopy, scanning electron microscopy and transmission electron microscopy on strains of both species showed them to make up separate species and found that the variety C. compressus var. hirtisetus should be raised to species level as C. hirtisetus comb. & stat. nov. We describe two varieties of C. contortus: the temperate cf. var. contortus and the tropical var. ornatus var. nov. Characters for species delineation comprise a combination of light microscopically visible features, such as valve size and shape and number of chloroplasts. Furthermore, resting spore morphology and the number of labiate processes on the terminal valve seen in electron microscopy (EM) can be used to separate the two species, as well as molecular characters.

Thalassiosira sundarbana sp. nov. (Bacillariophyta), an estuarine diatom from Sundarbans mangrove ecoregion based on morphology and molecular phylogeny

SummaryA new species of diatom, Thalassiosira sundarbana, is described based on light and scanning electron microscopy along with molecular phylogeny. The specimen was collected from Chemaguri creek of the Indian part of Sundarbans mangroves, and subsequently a clonal culture was established. Thalassiosira sundarbana possess variable numbers of occluded processes, and one labiate process on the valve face. Valve margin is ribbed and areolae are fasciculated on the valve face. Two rings of strutted processes are present on valve face. Strutted processes are also scattered on the valve face apart from the presence of two rings. Valvocopula and copula have rows of pore, and pleurae are hyaline. Bayesian analyses of nuclear encoded small subunit (SSU) rDNA and plastid encoded rbcL gene confirmed that T. sundarbana is phylogenetically novel. Salinity tolerance experiment with the clonal culture of T. sundarbana showed that this isolate can grow in salinity ranging from 10–35 psu. The maximum growth rate was observed in 15 psu salinity (0.5 divisions 24 h−1). On the basis of morphological features and molecular phylogeny, this clonal isolate is considered as a new estuarine species of Thalassiosira.

Morphological features and new description of the fossil species Thalassiosira dolmatovae (Bacillariophyceae)

Specimens of the Neogene marine diatom Thalassiosira dolmatovae have been studied with a scanning electron microscope for the first time. The observations revealed the morphological features typical of this species including arrangement of different kinds of processes. T. dolmatovae has one single subcentral strutted process, a ring of marginal strutted processes, a labiate process located at the margin and enclosed by two strutted processes. Marginal strutted processes with outward extensions and without inward extensions have internal openings surrounded by 4 satellite pores. The location of a labiate process not on the valve face and the presence of marginal strutted processes with outward extensions indicate that the studied species really belongs to genus Thalassiosira not to genus Shionodiscus. A valid description of T. dolmatovae is given.

A study on the fine structure of marine diatoms in Korean coastal waters: Genus Thalassiosira 5

Thalassiosira species were collected from October 2007 to January 2009 in an attempt to better understand species diversity of the genus Thalassiosira in Korean coastal waters. A total of 5 Thalassiosira species (T. concaviuscula, T. oceanica, T. partheneia, T. simonsenii and T. nanolineata) were identified here. Most species in this study were of small size, and 5 species were recorded for the first time in Korean coastal waters. Using a scanning electron microscope (SEM), we described distinctive characteristics of fine structure that proved to be important diagnostic characteristics for the identification of each species. The most important diagnostic characteristics for Thalassiosira species identification were the marginal strutted processes, the position of labiate processes, and the areolation. The differential characteristics of the species studied were: T. concaviuscula has a double layered external tubes on the marginal strutted processes; T. oceanica shows marginal ridges that are interlinked between the marginal strutted processes; the valve face of T. partheneia is fairly convex and its labiate process is positioned midway between two strutted processes; T. simonsenii is characterized by two labiate processes and somewhat coarse areolae; and, T. nanolineata has several central strutted processes and linear areolation.

A Study on the Fine Structure of the Marine Diatoms of Korean Coastal Waters - Genus Thalassiosira 3

A study on the fine structure of the marine diatom Thalassiosira has been carried out during the periods from January 2007 to March 2008 in Korean coastal waters. As the third series of the Thalassiosira species, a fine structure, description, distribution and taxonomic remarks of the six Thalassiosira species were observed by means of light microscope and scanning electron microscope. The critical features of Thalassiosira species were a shape of external tubes of marginal strutted processes and labiate process. Six species showed each different shape of external tubes, marginal strutted processes and labiate process. The shape of external tube was divided into five types: T shape of Thalassiosira curviseriata, small-rounded shape of T. lundiana, double-layer form and flame shape of T. nordenskioeldii, tulip shape of T. punctigera and tooth-shape of T. tenera. This external character may be able to key character for positive identification of the Thalassiosira species. Of these Thalassiosira lundiana, T. minuscula and T. tenera were new records for Korean coastal waters.

우리나라 황해의 해산 돌말류 Ditylum brightwellii (West) Grunow의 형태학적 특징에 의한 두 유형

This study deals with the taxonomy of the marine diatom Ditylum brightwellii (West) Grunow: shape, size and ratio, marginal ridge, labiate process, areolation, and seasonal distribution are all considered. Ditylum brightwellii were divided into two type; prism- and cylinder-shaped. Comparisons between specimens from the Yellow Sea were made on, (1) shape- prism types are prismatic-shaped and/or regular square or right-angled tetragon, cylinder types are cylinder-shaped and/or long right-angled tetragon in the girdle view, respectively; (2) size and ratiodiameters of prism types are 82.1 ± 2 µm, while those of cylinder types are 21.2 ± 5 µm and ratio of pervalvar axis/diameter- prism types cells are 1.0-1.5, but cylinder types are 3.9-5.5; (3) marginal ridges- prism types have dotted, while those of the cylinder-type cells have piece, slotted or fimbriated on the marginal ridge; (4) labiate process- both prism- and cylinder-types are central part in valve face, but length of labiate processes of prism types are longer than those of cylinder types; (5) cell margin- the girdle margin show many shallow furrows in prism type and smooth in cylinder type; (6) areolation- both prism- and cylinder-types are a radial pattern in the valve center, but areolae of prism types are larger than those of cylinder types; (7) seasonal distribution- cylinder types are dominated in summer and prism types in the other seasons.

REVISION OF ODONTELLA ATLANTICA (FRENGUELLI) SAR COMB. ET STAT. NOV. WITH COMPARISON TO TWO RELATED SPECIES, O. RHOMBUS (EHRENB.) KÜTZ. AND O. RHOMBOIDES R. JAHN ET KUSBER

Biddulphia rhombus var. atlantica was erected by Frenguelli from waters of the South Atlantic Ocean. A revision of its syntype series was carried out with light microscopy, a lectotype was chosen and compared with the lectotype of Odontella rhomboides (= Zygoceros rhombus), and with the lectotype of Odontella rhombus (= Denticella rhombus), designated in this paper. As there is no unmounted material available in the Frenguelli Collection, a SEM study was carried out on material collected in Buenos Aires Province coastal waters, Argentina. Differences in pattern of striation and distribution of labiate processes were established as the striking features to distinguish Frenguelli's taxon from the other two species. Based on the analysis of the fine structure the placement of Frenguelli's var. atlantica in the genus Odontella according to the modern concept of generic limits within the biddulphioid diatoms was confirmed and the taxon raised to species rank as Odontella atlantica, comb, et stat. nov.

CELL WALL MORPHOLOGY AND SYSTEMATIC IMPORTANCE OF THALASSIOSIRA RITSCHERI (HUSTEDT) HASLE, WITH A DESCRIPTION OF SHIONODISCUS GEN. NOV.

The centric diatom order Thalassiosirales includes all diatoms with a fultoportula (strutted process), a feature now recognized as a synapomorphy for the lineage. Within Thalassiosirales, Thalassiosira is perhaps the most taxonomically and morphologically diverse genus, and at least two distinct morphological groups have been recognized within it. Group “A” Thalassiosira species, which include the type species, T. nordenskioeldii, have short inward and long outward extensions of the strutted processes and a labiate process on the valve mantle. Group “B” species have exceptionally long inward and reduced outward extensions of the strutted processes, and a labiate process on the valve face. We collected and cultured Thalassiosira ritscheri, which has a combination of group A and B characters. It has a labiate process on the valve face and reduced outward extensions of the strutted processes. We show for the first time that T. ritscheri has short inward, A-type extensions of the strutted processes. A phylogenetic interpretation of these conditions suggests a close relationship between T. ritscheri and the traditionally held group “B” species. Species diagnosed by the autapomorphic condition of a labiate process away from the valve mantle, including many group “B” Thalassiosira species, are transferred into Shionodiscus gen. nov.

MOTILITY OF NON-RAPHID DIATOMS

The araphid diatom Licmophora hyalina's motility was observed in cultured material. Gliding movement was nearly straight and only towards the broader pole, and the colonies rotated. Although mucilage secretion was not observed with the light microscopy, the links between motility and the labiate process and/or the multiscissura are suggested. Other motile members in non-raphid (centric and araphid) diatoms are briefly reviewed. Several non-raphid species exhibit motility, suggesting that there might be more motile araphid diatoms.

남극 호냉성 미세조 Porosira pseudodenticulata의 형태와 분자적 자료

We have cultured more than 100 Arctic and Antarctic cryophilic microalgal strains in KOPRI culture collections of polar microorganisms (KCCPM). Among them, we tried to identify an Antarctic strain, KOPRI AnM0008 by morphological and molecular analysis. Nuclear SSU rDNA and plastid rbcL sequences were used to identify the strain. It was identified as Porosira pseudodenticulata based on SSU sequence data showing 99% identity with GenBank X85398. This result was supported by morphological features like solitary labiate process, external foramina and internal cribra by optical and scanning electron microscope. Morphological identification and molecular analysis on polar cryophilic microalgae will be accomplished to construct the databases for KCCPM.

Valve development in the diatom family Asterolampraceae H. L Smith 1872

Seven extant and two fossil species within the family Asterolampraceae were studied with light and electron microscopy. The sequence of stages in valve morphogenesis was determined for those species where presumably developing valves were found. Occasionally valves from sibling cells were found still attached to one another, as they had been within the mother frustule during the process of cell division, giving evidence that forming, not eroding valves were being observed. Hollow rays are the most distinctive feature of genera in this family and appear to be formed by the marginal fusion of “tuning fork”-like structures emanating from a central or eccentric annulus. Rimoportulae, formerly termed labiate processes because of their lip-like internal structure, form at the marginal end of the rays where the “tines” of the forks apparently fuse. The structure of cribra, coverings over the loculate areolae, is very different in the species studied and we show the mode of development also varies.

Étude biostratigraphique et paléoenvironnementale des diatomées pyritisées de l'intervalle Paléocène supérieur–Éocène inférieur du sondage de Saint-Josse (France)

Resume La presente etude analyse le contenu en diatomees pyritisees de l'intervalle Paleocene–Eocene du sondage CC82 de Saint-Josse. Saint-Josse est localise en France, dans le nord du bassin de Paris et a les coordonnees suivantes : X = 555 000, Y = 307 324 et Z = 56,9 m. Normalement constituees d'un frustule siliceux, les diatomees des sediments concernes ont ete pyritisees, d'une part, par epigenie transformant le squelette d'opale-A en pyrite ; d'autre part, par cristallisation de pyrite au sein de la cavite interne des diatomees ou dans le vide laisse dans le sediment apres dissolution du frustule formant ainsi des moules internes de celles-ci (steinkerns). Les cristaux de pyrite ont developpe differentes formes : cubes (parfois a troncature des sommets), pyritohedres, octahedres, framboides,… L'epigenie preserve toutes les ornementations des diatomees (velum, areoles, processus labies,…) tandis que le moule ne conserve que la forme globale ainsi que certaines structures du frustule telle la ceinture. Cependant, la pyrite est alterable et destructible par oxydation ce qui justifie l'etude d'un sondage et non d'une coupe soumise aux agents atmospheriques et aux eaux de percolation. Le sondage de Saint-Josse a l'avantage de montrer une succession des facies du Paleocene superieur et de l'Eocene basal jusque l'Ypresien. Il comporte plusieurs unites marines, saumâtres et continentales. Parmi celles-ci, l'unite de Sorrus, appartenant au Groupe de Thanet, revele un paleoenvironnement a cachet continental marque par la Paralia siberica var. laevis caracteristique de milieux estuariens. L'unite de Saint-Aubin contient des diatomees franchement saumâtres ( Actinoptychus senarius , Coscinodiscus commutatus et Stellarima microtrias ) ainsi que des diatomees marines ( Coscinodiscus morsianus var. morsianus , Coscinodiscus morsianus var. moelleri , Fenestrella antiqua , Odontella heibergii , Rhizosolenia sp. 1 et Trinacria regina ). L'etude de l'abondance de ces taxons montre que l'unite de Saint-Aubin est caracteristique d'un paleoenvironnement lagunaire saumâtre avec des influences marines et dont le caractere saumâtre augmente vers son sommet. Deux assemblages distincts de diatomees sont definis. L'assemblage D1 est caracterise par la presence de rares T. regina et, principalement, par l'abondance de C. morsianus var. morsianus et C. morsianus var. moelleri . En revanche, l'assemblage D2, se situant dans la partie superieure de l'Unite de Saint-Aubin, est caracterise par l'abondance et l'acme de F. antiqua ainsi que la nette diminution jusqu'a disparition de C. morsianus var. morsianus et Coscinodiscus var. moelleri . La zone NSP4 de King (1983) est delimitee a la base par la premiere apparition de la F. antiqua et au sommet par l'acme de cette espece. L'intervalle etudie du sondage de Saint-Josse, a l'exception des unites du Mont-Hulin et du Château de la Bruyere, correspond a cette zone NSP4. Les sous-zones NSP4a et NSP4b, definies par Mitlehner (1996), sont egalement observees dans l'intervalle etudie. La zone NSP4a est attribuee aux Unites de Sorrus, La Calotterie, Bois Gorguette, Le Goulet et la partie inferieure de Saint-Aubin ; en revanche, la partie superieure de l'Unite de Saint-Aubin correspond a la sous-zone NSP4b. Dans le bassin de Paris, il est possible de correler les biozonations de diatomees a la biozonation de Martini (1971) du moins pour les zones NP9 et NP10. Tenant compte de l'abondance elevee de la F. antiqua et de son pic d'abondance a 46 % (echantillon 17,87), la partie superieure de l'unite de Saint-Aubin (intervalle 17,87–16,20) peut etre correlee par l'intermediaire des biozonations de King (1983), adaptees par Mitlehner (1996), a la zone NP10 de Martini. L'intervalle 34,60–18,75, par l'abondance relative elevee de C. morsianus var. moelleri , peut etre correlee a la zone NP9 de Martini. De plus, les assemblages de diatomees observes dans le sondage de Saint-Josse sont plus ou moins identiques a ceux du bassin de la Mer du Nord et permettent des correlations lithostratigraphiques. D'une part, les unites de Sorrus, La Calotterie, Bois Gorguette, Le Goulet et la partie inferieure de Saint-Aubin sont correlees a la Formation Sele du bassin de la Mer du Nord. D'autre part, la partie superieure de l'Unite de Saint-Aubin correspond a la Formation Balder.

Membrane organisation and dynamics in the marine diatom Coscinodiscus wailesii (Bacillariophyceae)

The membrane dye FM1-43 was used to visualise membrane internalisation in living cells of the marine centric diatoms Coscinodiscus wailesii and Thalassiosira punctigera . The results revealed dynamic and selective membrane trafficking and several cellular structures which have not been described in light microscopical studies. Intimate and regular contacts were found between the plasma membrane and the labiate processes and the inner face of the frustule in C. wailesii . The central cytoplasmic region close to the tonoplast and growing parts of the silica deposition vesicles became labelled, indicating that they were involved in membrane recycling. We never observed labelling of chloroplasts, nucleus or the vacuolar contents. These studies also revealed a novel perinuclear region that appeared not to show significant membrane turnover. When the cytoplasm was impaled with a micropipette, membranous material rapidly accumulated at the tip of the micropipette, presumably expelling it from the protoplast. This could be an effective defence mechanism against certain invasive pathogens, and further illustrates the highly dynamic nature of the endomembrane system.

Spatial determinants in morphogenesis: Recovery from plasmolysis in the diatom Ditylum

Ditylum cells are enclosed in a rigid wall consisting of two "valves" (end walls) connected by "girdle bands." A hollow spine, the Labiate Process (LP), extends from each valve and a stable cytoplasmic strand connects its base with the nucleus. We investigated whether cells might possess "spatial determinants" for controlling their internal organization and wall morphogenesis. Upon plasmolysis, cells contracted into a spherical protoplast detached from the wall. Recovery was initiated by growing filopodia that "searched" the inside of the wall. Some attached to the inside corners, generating tension that could temporarily displace the protoplast. Others consolidated into the strand connecting nucleus with the LP. The protoplasts soon expanded and cells recovered: some divided immediately, the rest within 24 h. When recently divided cells were plasmolysed, their nascent valves were exocytosed. These were ignored by the filopodia during recovery. Later, protoplasts secreted a new valve, while the nascent valves were discarded. The interphase microtubule (MT) cytoskeleton radiates from a central Microtubule Center. A thicker bundle connects the nucleus to each LP. Plasmolysis destroyed the MT cytoskeleton; its re-establishment matched growth of the filopodia. The anti-MT drug oryzalin prevented filopodial extension while existing filopodia retracted, except those stabilized by attachment to the corners of the cell and the LP. Several anti-actin agents had relatively little effect. However, one, mycalolide B, caused the nucleus to be extruded from the protoplast by a bundle of MTs. We conclude that the geometry of the wall could provide spatial information to which the MT-cytoskeleton/filopodia respond.