STRUCTURE AND PHYSIOLOGY OF THE HAPTONEMA IN CHRYSOCHROMULINA (PRYMNESIOPHYCEAE). II. MECHANISMS OF HAPTONEMATAL COILING AND THE REGENERATION PROCESS1

The axoneme in the free part of the haptonema in Chrysochromulina acantha Leadbeater & Manton and C. simplex Estep et al. consists of seven single microtubules, except in the extreme distal swelling where, in C. simplex, there are only three microtubules. In the extended haptonema, the microtubules are arranged in a ring though they are not evenly spaced, the gap between two of the microtubules being larger than that between any other neighboring pairs. In the coiled haptonema, rearrangement of the microtubules occurs so that the ring becomes distorted and the microtubules form two superposed arcs. A sliding microtubule mechanism is considered as a means by which haptonematal movement might be affected, and this is discussed in relation to the fine structure of both embedded material and negatively stained demembranated cells. We show that haptonematal coiling is dependent on the presence of calcium ions and that an external concentration of between 10^?6 and 10^?7 M Ca²⁺ is the threshold below which the frequency of coiling on cell death is reduced. The results of experiments using ethylene bis-(oxyethylenenitrilo)-tetracetic acid (EGTA) and lanthanum ions to control extracellular and intracellular Ca²⁺ concentrations are discussed in terms of both external free calcium and intracellular pools. We also show that haptonematal regeneration following excision begins with a short lag phase. This is followed by a period of rapid growth, decreasing after approximately 4 h. Full haptonematal regrowth is not achieved until after 12–15 h. The rate of haptonematal regeneration is strongly affected when the flagella are regenerating simultaneously. These observations are interpreted in terms of competition for intracellular precursors.     

THE FLAGELLAR APPARATUS OF CHRYSOCHROMULINA SP. (PRYMNESIOPHYCEAE)1

The flagellar apparatus of an undescribed species of Chrysochromulina Lackey that bears “eyelash” scales is reconstructed. The transitional region consists of two transitional plates each with an axosome, with no stellate pattern between them. Fine osmiophilic rings lie between the flagellar membrane and the outer doublets in the transitional region. The two jagella and the haptonema are inserted in a subapical depression that is lined ventrally by a spine-like projection formed by one of the parietal chloroplasts. The angles of insertion are similar to those of some other Chrysochromulina species in that both the haptonema and the right basal body lie at an extreme angle to the left basal body. The connectives of the apparatus consist of a striated distal band with a dorsal extension to the R1 and a ventral extension overlying the R2, a striated distal accessory band, an auxiliary connective from the right basal body to the adjacent ventral chloroplast, a well-developed intermediate band, two striated proximal bands, and a striated proximal accessory band. Of the microtubular roots in this Chrysochromulina species, three are associated with the left side of the cell (an R1 of 8+3; a small crystalline compound root, the R1C, associated with the R1; an R2 of three micro-tubules), and two are associated with the right basal body (an R3 of 2/2 microtubules with which the single-stranded R4 converges to form a 2/2+1 and then a 2/3 tiered arrangement). Comparisons are drawn with other species in the genus and related genera, particularly Prymne-sium.     

CHRYSOCHROMULINA BREVITURRITA SP. NOV., A NEW FRESHWATER MEMBER OF THE PRYMNESIOPHYCEAE1

Chrysochromulina breviturrita sp. nov. is described as a new haptonema-bearing member of the freshwater Prymnesiophyceae. It is ca. three times larger than the only other known freshwater member of the genus (C. parva Lackey)and possesses a haptonema only ca. 0.2–0.3 as long as the haptonema of C. parva. Two equal flagella (1.5–2 as long as the haptonema), a large contractile vacuole, two parietal plasties, a single pyremid, nucleus, Chrysolaminarin-like droplets and a food vacuole are features readily observed with the light microscope. Dried and shadoweast whole mounts examined with the electron microscope reveal the cell surface covered with two types of small, delicate scales: outer spined scales with a clubshaped terminus and with the spine anchored to a circular to oval base-plate by 2–6 (7) branching arms; and, spineles oval plate scales with concentric lines and radiating ridges on one face and parallel ridges on the other. C. breviturrita has been found in nine lakes in Ontario (Canada). Pereliminary observations suggest that it is an important component of lake plankton and has probably not been delected in previous work, more because of its fragility than because of its scarcity. Living specimens are a prerequisite for initial identification, since cells frequently rupture and haptonemata are often lost when the organisms are killed with the commonly used fixatives.     

ULTRASTRUCTURE OF THE FLAGELLA OF THE COLORLESS PHAGOTROPH PERANEMA TRICHOPHORUM (EUGLENOPHYCEAE).II. FLAGELLAR ROOTS1

Peranema trichophorum (Ehrenberg) Stein, a colorless phagotrophic euglenoid flagellate, has a typically euglenoid microtubular root complement. Striated root components, relatively uncommon in euglenoids, are connected to the basal bodies and to a microtubular root. The flagellar system of Peranema consists of three unequal microtubular roots which extend anteriorly beneath the reservoir membrane, and narrow-band striated roots (periodicity = 29–33 nm) which connect one of the four basal bodies to the movable rodorgan of the feeding apparatus. An inter basal body striated fiber forms a three-way connection between one particular microtubular root, a flagellar basal body, and the striated roots. A striated fibril (periodicity = 18–25 nm), which may be an extension of the striated root system, extends beneath the reservoir membrane. Associated with the striated fibril and the striated roots are cisternae of smooth endoplasmic reticulum.     

PLOIDY ANALYSIS OF THE TWO MOTILE FORMS OF CHRYSOCHROMULINA POLYLEPIS (PRYMNESIOPHYCEAE)1

In some cultures of the flagellate Chrysochromulina polylepis Manton et Parke, established from cells isolated from the massive bloom in Skagerrak and Kattegat in 1988, we observed, two motile cell types. They were termed authentic and alternate cells and differed with respect to scale morphology. To investigate whether or not the two cell forms were joined in a sexual life cycle, the relative DNA content per cell and relative size of cells of several clonal cultures of C. polylepis were determined by flow cytometry. Percentages of authentic and alternate cells in the cultures were estimated by transmission electron microscopy. Pure authentic cultures (α) contained cells with the lowest level of DNA and were termed haploid. Two pure alternate cultures (β) contained cells with double the DNA content of authentic cells and were termed diploid. Other pure alternate cultures contained haploid cells only, or both haploid and diploid cells. Three cell types were observed, each capable of vegetative propagation: authentic haploid, alternate haploid, and alternate diploid cells. Both the haploid and diploid alternate cells were larger than the haploid authentic cells. Cultures containing diploid cells appeared unstable: cell type ratio and ploidy ratio changed during the experiment where this cell type was present, particularly when grown in continuous light. In contrast, cultures with only haploid cells remained unchanged at all growth conditions tested. Light condition may influence cell type ratio and ploidy ratio. Our attempt to induce syngamy by mixing different authentic haploid clones did not result in mating. Assuming that the authentic and alternate cell types are of the same species, the life cycle of C. polylepis includes three flagellated scale-covered cell forms. Two of the cell types are haploid and may function as gametes, and the third is diploid, possibly being the result of syngamy.     

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF DINOBRYON CYLINDRICUM (CHRYSOPHYCEAE)1

The three-dimensional structure of the flagellar apparatus of Dinobryon cylindrioum Imhof. (UTEX no. LB 2266) was determined using serial section reconstruction. Four microtubular rootlet systems (R₁, R₂, R₃, and R₄)and a rhizoplast are present, following the general pattern found in other chrysophytes. The R₁ rootlet, containing seven microtubules, originates at the basal body of the long flagellum that bears mastigonemes (F₁). The R₁ rootlet forms an arc which curves in clockwise direction (when viewed from the anterior end of the cell) approximately halfway around the pit from which the short smooth flagellum (F₂) emerges. Numerous microtubules cascade from the exterior-facing side of this rootlet to the tail of the cell. The R₂ rootlet originates between the F₁ and F₂ basal bodies, is attached to the F₁ basal body by a fibrous connection, and forms a clockwise arc above the R₁ rootlet. This rootlet extends approximately one quarter of the way around the pit. The R₃ rootlet system originates as a trough-shaped band of six microtubules spanning the distance between the proximal ends of the F₁ and F₂ basal bodies. The six-membered rootlet splits into two parts, designated R₃ and R₃. Both parts circle the pit in counter-clockwise direction, pass beneath the F₂ basal body, and descend into the cell alongside the chloroplast. The R₄ rootlet originates in fibrous material, passes diagonally over the top of the F₂ basal body, forms a clockwise loop at least three quarters of the way around the pit to the interior of the R₃ and R₃ rootlets, and ends in the cytoplasm. Similarities of rootlet origins and other details of the flagellar apparatus of D. cylindricum with those of other heterokont organisms reinforce the idea that these organisms are phylogenetically related.     

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF UROGLENA AMERICANA (CHRYSOPHYCEAE)1

The three-dimensional structure of the flagellar apparatus of Uroglena americana Calkins (Uroglenopsis americana [Calkins] Lemmerman) was determined using serial section reconstruction. The three microtubular rootlet systems (R₂, R₃, and R₄) follow the general pattern found in other chrysophytes. The R₂ rootlet originates between the basal bodies of the mastigoneme-bearing long flagellum (F₁) and the short smooth flagellum (F₂) and is attached to the former by a fibrous connection. The R₃ rootlet system originates as a trough-shaped band of six microtubules spanning the distance between the proximal ends of the F₁ and F₂ basal bodies. The six-membered rootlet splits into two parts (designated R₃ and R₃) which circle the depression from which the F₂ flagellum emerges in counter-clockwise direction. These two rootlets pass beneath the F₂ basal body and descend into the cell alongside the chloroplast. The R₄ rootlet originates in fibrous material which passes diagonally over the F₂ basal body, forms a clockwise loop about three-quarters of the way around the depression, and ends in the cytoplasm. In place of a typical chrysophyte R₁ rootlet, U. americana has a different array of microtubules attached to the F₁ basal body which we have designated the descending rootlet (DR). This rootlet is a hairpin-shaped structure lying just below the surface of the cell; its longitudinal axis is predominantly parallel to the longitudinal axis of the cell. The DR resembles the bypassing rootlet which occurs in phaeophyte zoospores. Other chrysophytes may possess rootlets which are similar to the DR found in Uroglena.     

FLAGELLAR ROOTS AND THE RESERVOIR CYTOSKELETON OF COLACIUM LIBELLAE (EUGLENOPHYCEAE)1

The three flagellar roots of Colacium Ehrenberg give rise to the three microtublar bands of the reservoir cytoskeleton. The dorsal root (DR) originates at the basal body (bb1) of the emergent flagellum. It is initiated on the left side of the cell, runs toward the right side under the posterior end of the reservoir and thence anteriorly in a spiral path over the dorsal surface of the reservoir until it terminates on the left side of the eyespot. Along its length, it appears to initiate a dorsal band (DB) which forms the major dorsal portion of the reservoir cytoskeleton—the dorsal microtubules (DMT). Two roots originate at the basal body (bb2) of the non-emergent flagellum. The ventral root (VR) runs up the left side of the cell and initiates the band of microtubules which forms part of the presumptive vestigial cytopharynx. Therefore, it forms the reinforcing microtubules (MTR) of Colacium. The intermediate root (IR) forms the para-reservoir microtubules (PMT). Flagellar root correlation with the reservoir cytoskeletal bands strengthens their homologies with the bodonid bands and further supports the hypothesis that the euglenoids are derived from the kinetoplastid flagellates.     

TWO MOTILE STAGES OF CHRYSOCHROMULINA POLYLEPIS (PRYMNESIOPHYCEAE): MORPHOLOGY,GROWTH, AND TOXICITY1

Eight months after the 1988 bloom of Chrysochromulina polylepis Manton et Parke in Skagerrak and Kattegat, off the coasts of Norway, Sweden, and Denmark, an alternate cell type carrying a scale complement different from that of authentic C. polylepis appeared in some clones isolated from the bloom. The cultures were recloned, and the development of the new clones was monitored. In clones with 100% cells of the alternate type, authentic cells reappeared, suggesting that the alternate cell type is a stage in the life cycle of C. polylepis and that transition between cell types occurs in both directions. Growth rates of clone cultures (termed a cultures) producing exclusively authentic cells, and of clone cultures (termed β cultures), capable of producing the alternate cell type, were compared at various combinations of temperature and photon fluence rate. The β cultures were less tolerant of high temperatures and photon fluence rates (≤20° C, 570 μmol photons·m^?2·s^?1) than were the α cultures. At lower temperatures and photon fluence rates (≤16° C, ≤90 μmol photons·m^?2·s^?1ss), β cultures grew better than α cultures. Relative abundance of the two cell types in β cultures changed in an apparently random manner during these experiments. Preliminary results from flow cytometric analyses indicated that cells of the alternate type were about twice the size and contained an equal or smaller amount of DNA per cell compared to the authentic cells. The β cultures were less toxic to Artemia nauplii than were the a cultures. Three other Chrysochromulina species tested were apparently nontoxic.     

STRUCTURE AND SIGNIFICANCE OF THE CRYPTOMONAD FLAGELLAR APPARATUS. I. CRYPTOMONAS OVATA (CRYPTOPHYTA)1

The absolute configuration of the flagellar apparatus in Cryptomonas ovata has been elucidated and found to be similar to that reported for Chilomonas paramecium. Variations apparent in the flagellar apparatus of Cryptomonas ovata include the presence of striations in the mitochondrion associated lamella, a rhizostyle which does not bear wing-like extensions from the microtubules and does not lie close to the nucleus, and a striated fibrous anchoring structure associated with one basal body which has not hitherto been described. The flagellar apparatus also includes a four stranded microtubular root which traverses into the anterior dorsal lobe of the cell, a striated fibrous root which is associated with a five stranded microtubular root, and a two stranded Cr root. The homologous nature of these roots to those in the larger cryptomonads is discussed in relation to the apparent reduction in flagellar apparatus size and complexity among the smaller cryptomonads. A diagrammatic reconstruction of the flagellar apparatus of Cryptomonas ovata is also presented.     

DEVELOPMENT OF THE FLAGELLAR APPARATUS AND FLAGELLAR POSITION IN THE COLONIAL GREEN ALGA PLATYDORINA CAUDATA (CHLOROPHYCEAE)1

The ultrastructure of the flagellar apparatus in pre-inversion and inversion stages of Platydorina resembles that of Chlamydomonas in having 180° rotational symmetry and clockwise absolute orientation. Basal bodies are in a “V” configuration and connected by one distal and two proximal fibers. Alternating two- and four-membered microtubular rootlets are cruciately arranged. During maturation, the basal bodies rotate and separate, and 180° rotational symmetry is lost. Simultaneously, each proximal fiber detaches from one of the functional basal bodies, and the distal fiber detaches from both. The mature apparatus has widely separated and nearly parallel basal bodies. Flagellar orientation in Platydorina is completed just after inversion and a flattening of the colony called intercalation, resulting in the pairs of flagella of neighboring cells extending from the colony in opposite directions in an alternating fashion. Flagellar orientation and separated basal bodies minimize the interference between the flagella of neighboring cells. Basal bodies and rootlets of the two intercalated halves of a colony rotate, resulting in the effective strokes of the flagella of every cell being towards the colonial posterior. The flagella of each cell beat with an effective stroke in the direction of the two inner rootlets. The flagella have an asymmetrical ciliary type beat. The rotated, separated, and parallel basal bodies, together with the nearly parallel rootlets probably are adaptations for movement of this colonial volvocalean alga. The flagellar apparatus in immature stages of Platydorina lends support to the suggestion that the alga has evolved from a Chlamydomonas-like ancestor.     

SOME PRYMNESIACEAE (HAPTOPHYTA,PRYMNESIOPHYCEAE) FROM THE MEDITERRANEAN SEA,WITH THE DESCRIPTION OF TWO NEW SPECIES: CHRYSOCHROMULINA LANCEOLATA SP. NOV. AND C. PSEUDOLANCEOLATA SP. NOV.1

Five species belonging to the family Prymnesiaceae (one Prymnesium and four Chrysochromulina) have been identified in cultures obtained from water collected in the Bay of Banyuls‐sur‐Mer (Mediterranean Sea, France) using LM, SEM, and TEM. Two are described as new species, Chrysochromulina lanceolata sp. nov. and C. pseudolanceolata sp. nov. Both species are large and lanceolate with an acute posterior and two anterior arms. They are easily detectable with LM but difficult to distinguish to species level with live cells, without experience. EM reveals two completely different scale patterns in the two species. Cells of C. lanceolata are 21–38 μm long, 7–12 μm wide, and 3–7 μm thick. They possess two subequal flagella (30–51 and 29–44 μm), and the haptonema is shorter than the flagella (23–37 μm). The cell body is covered by plate and spine scales. Cells of C. pseudolanceolata sp. nov. are slightly smaller (15–18 × 6–8 μm) with more rounded extremities, two subequal flagella (19–26 and 17–24 μm), and the haptonema is longer than the flagella (about 35 μm). Three types of plate scales are observed in this species. Other findings are C. alifera Parke et Manton and C. throndsenii Eikrem (a new record for the Mediterranean Sea). Prymnesium faveolatum Fresnel, a new toxic species recently described, is illustrated with both LM and SEM.     

STRUCTURE AND ABSOLUTE CONFIGURATION OF THE FLAGELLAR APPARATUS IN THE ISOGAMETES OF BATOPHORA (DASYCLADALES,CHLOROPHYTA)1

The overall appearance of the flagellar apparatus in the isogametes of Batophora oerstedii. J. Ag. is most like that which occurs in motile cells of the Ulvophyceae. Like other Ulvophyceae, the basal bodies overlap and are arranged in the 11/5 configuration, microtubular roots are arranged in a cruciate pattern and system II striated fibers are present. The basal body connective which generally lacks striation in the Ulvophyceae is clearly different in Batophora, being composed of two large non-striated halves which connect to the anterior surface of each basal body and are then connected to one another by a distinctly fibrous centrally striated region. This variation in the basal body connective and the presence of two posteriorly directed system II striated fibers is clearly different from homologous structures reported in siphonous green algae of the Caulerpales. Based upon these variations and similarities among flagellar apparatus components in siphonous green algae, it is suggested that the Dasycladales and Siphonodadales are more closely related to one another than to the Caulerpales.     

ULTRASTRUCTURE OF PRYMNESIUM NEMAMETHECUM SP. NOV. (PRYMNESIOPHYCEAE)1

Based on material collected from Cape Town, a new sand-dwelling, marine species of Prymnesium is described. Using light and electron microscopy, Prymnesium nemamethecum sp. nov. has been found to resemble other species of the genus in size, organelle arrangement, and swimming behavior. It differs from other described species in that it has three types of scales, one of which is confined to the region of appendage insertion and forms a sheath of simple plate scales over the haptonema. In addition, the scales constituting the proximal body scale layer(s) are unusual because they are not simple plate scales but are specifically ornamented.     

FINE STRUCTURE OF THE ZOOSPORE OF OEDOCLADIUM CAROLINIANUM (CHLOROPHYTA) WITH SPECIAL REFERENCE TO THE FLAGELLAR APPARATUS1, 2

Ultrastructure of the motile zoospore has been investigated in Oedocladium catolinianum & Hoffman. An unwalled zoospore is usually produced from the contents of a terminal vegetative cell and consists of two principal regions: a small anterior dome and a larger body region; a ring of flagella marks the juncture of these two areas. Chloroplast inclusions consist of thylakoids, mature and incipient pyrenoids, starch and striated microtubules; no eyespot has been observed. Zoospores appear to possess permanent contractile vacuoles with numerous accessory vacuoles, coated vesicles and occasionally coated tubules. The cytoplasm of the dome contains numerous mitochondria ER and golgi bodies, as well as two distinct types of vesicles. The first contains an electron-dense; granular core and is surrounded by a loose, sinuate membrane. The second vesicle is electron-opaque and is found at the apex of the dome: it contains mucopolysaccharides employed during zoospore adhesion. A complex flagellar apparatus encircles the lower region of the dome. It consists of ca. 30–65 flagella, a ring-shaped fibrous band, flagella roots and additional supporting material. The flagella and roots alternate with one another beneath the fibrous band. The compound flagellar roots consist of two superimposed components: an outer ribbon-like unit composed of three microtubular elements and a single striated inner component. A band of support material lies beneath the proximal end of the basal bodies. It is a continuous fibrous band, although it often appears as three distinct, repetitive units.     

THE OCCURRENCE AND STRUCTURE OF FLAGELLAR SCALES IN SOME FRESHWATER CRYPTOPHYTES1

Flagellar scales were found in seven out of eleven fresh-water cryptophytes investigated by shadowing whole cells. All scales examined were 140 to 170 nm in diameter and had a basic seven-sided rosette pattern with delicate interlacing. The results of this study indicate that flagellar scales are common in cryptophytes .     

DEVELOPMENT OF THE FLAGELLAR APPARATUS AND FLAGELLAR ORIENTATION IN THE COLONIAL GREEN ALGA GONIUM PECTORALE (VOLVOCALES)1

Vegetative cells of Gonium pectorale have a fine structure similar to that of Chlamydomonas. In addition, three zones comprise an extracellular matrix; a fibrillar sheath and tripartite boundary surround individual cells, and a fragile capsule zone surrounds the entire colony. Cytokinesis is accomplished by a phycoplast and cleavage furrow. The flagellar apparatus of the immature vegetative cell of this colonial alga is similar to that of Chlamydomonas, but the basal bodies are slightly separated at their proximal ends. The four microtubular rootlets alternate between two and four members. During development, the basal bodies become further separated and nearly parallel. The distal fiber is stretched, but it remains attached to both basal bodies. At maturity, the basal bodies of peripheral cells of the colony have rotated in opposite directions on their longitudinal axes resulting in a displacement of the distal fiber to one side, an asymmetrical orientation of the rootlets and loss of 180° rotational symmetry. Central cells remain similar to Chlamydomonas in that basal bodies do not rotate, rootlets are cruciate, the distal fiber remains medially inserted and 180° rotational symmetry is conserved. A “pin-wheel” configuration of flagellar pairs and the orientation of parallel rootlets toward the colony perimeter probably accounts for the rotation of the colonies during forward swimming. In addition, these ultrastructural features support the traditional placement of G. pectorale as an intermediate between the unicellular Chlamydomonas and the more complex colonial volvocalean genera.     

COMPARATIVE ANALYSIS OF THE FINE STRUCTURE OF YOUNG AND ADULT INDIVIDUALS OF DUNALIELLA SALINA (POLYBLEPHARIDACEAE,CHLOROPHYCEAE) WITH EMPHASIS ON THE FLAGELLAR APPARATUS1

Individuals of Dunaliella salina (Dunal.) Teod. change their shape during ontogenesis. Here we describe the fine structure of this species with emphasis on distinctions between young and adult individuals. The cell coat is present at early stages of cell development and may be synthesized by vesicles of nuclear membrane-associated endoplasmic reticulum. Scanning electron microscopical observations show differences in the surface pattern of the cell coat in young and adult cells. The nucleus of young cells is more or less spherical, whereas that of adult cells is pyriform. The Golgi apparatus is positioned immediately under the basal bodies and consists of three dictyosomes in young cells and six to eight dictyosomes in adult cells. The flagellar apparatuses of young and adult cells have a 1/7 o'clock (i.e. clockwise) displacement of basal bodies and are grossly similar, but there are subtle differences between specific components. Two non-axonemic basal bodies (1′, 2′) appear in a plane perpendicular to that determined by the flagella-bearing basal bodies (1, 2). The cruciate microtubular rootlet system has a 4–2–4–2 alternation pattern. In adult cells, rhizoplasts emerge from each terminal body and run parallel to the four rootlets.     

FINE STRUCTURE OF THE MALE AND FEMALE GAMETES OF ATRACTOMORPHA PORCATA (SPHAEROPLEACFAE,CHLOROPHYTA) WITH EMPHASIS ON THE DEVELOPMENT AND ABSOLUTE CONFIGURATION OF THE FLAGELLAR APPARATUS1

Gametogenesis in Atractomorpha porcata Hoffman was initiated b the synchronous mitotic division of nuclei within a multinucleate gametangium. Uninucleate gametes were subsequently produced following two series of cytokinetic divisions. The first series involved the formation of phycoplast microtubules (phycoplastic cytokinesis), whereas the second series did not (nonphycoplastic cytokinesis). Centrioles were connected by a rudimentary striated distal fiber by the time they migrated to the planes of division preceding the first series of cytokinetic division. These first divisions produced binucleate gametocytes. A well-developed flagellar apparatus lay near the cell surface in close proximity to each nucleus of the gametocyte prior to the second series of cytokinetic divisions that produced the uninucleate gametes. As seen in apical view, the paired basal bodies were directly opposed, with no lateral displacement of their longitudinal axes. In lateral view, the paired basal bodies diverged from one another at an angle of 130–180° (female) or 170–180° (male) and were connected by an arched, distal striated fiber about 670–750 nm long and 600 nm at its widest part. Four electron-opaque, pyramid-shaped lateral bodies flanked the basal bodies in close contact with their undersurfaces. The flagellar roots demonstrated a cruciate arrangement, with s = 6–9 over 1 (female gametes) or 7–10 over 1 (male gametes) microtubules and d= 2 microtubules. In male gametes, one of the multistranded roots was located close to the eyespot, and a second system of cytoskeletal microtubules was detected internally. Based on gamete ultrastructure, Atractomorpha porcata appears to be the most undifferentiated member of the genus.     

LOCALIZATION OF CA2+-STIMULATED ATPASE IN THE COCCOLITH-PRODUCING COMPARTMENT OF CELLS OF PLEUROCHRYSIS SP. (PRYMNESIOPHYCEAE)1

Cell homogenates of Pleurochrysis sp. (CCMP299) were fractionated by means of sucrose gradients. Ca²⁺-stimulated ATPase (EC 3.6.1.3., ATP phosphohydrolase) was associated primarily with the plasma membrane, Golgi, and high density (1.21 g·cm^?3) membranous structures. Ca²⁺-stimulated ATPase was highly enriched in the latter. Based on treatments with Triton X-100 and NBD ceramide, we conclude that the high-density structures were membrane-delimited organelles. These vesicle-like organelles contained complex polysaccharides, a high concentration of calcium, and, upon microscopic examination, structures resembling coccoliths. These findings are consistent with observations on the known composition of coccoliths and the presumed mineralizing function of the sub-cellular coccolith-producing compartment. The high-density vesicles were linked to the Golgi by means of colchicine-sensitive materials, presumably microtubules. These data and prior ultrastructural observations by other investigators indicating vectorial assembly and secretion suggest that the subcellular movement of the newly formed coccoliths may be directed and/or powered by colchicine-sensitive cytoskeletal elements. We interpret the data to mean that the high-density vesicles represent the coccolith-producing compartment previously observed by others in electron micrographs.