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Aulacodiscus kittonii. A, F-M, Scanning Electron Microscopy; B-E, Light Microscopy. A. Frustule in conectival view. B-E. Valves with four, six, eight and ten labiate processes respectively. F-G. External and internal views of valves with four labiate processes. H. Internal view of valve with six labiate processes. I-J. External and internal views of valves with five labiate processes. K. External view of areolae in radial rows and lacking velum. Central rosette with angular areolae. Submarginal labiate process. L. External velum of areolae. M. Papillae on the marginal walls of each areola. Scale bars: A, F-J = 20 μm; B-E = 40 μm; K = 10 μm; L = 5 μm; M = 1 μm.
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The so-called “surf diatoms” constitute a small group of species that are present with great abundance in the surf zones of some sandy beaches where often the accumulations are dominated only for one of these species. They adhere to air bubbles generated by wave action forming green or brown patches that float in the surf zone, remaining as long st...
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... cells of A. kittonii are solitary, circular in outline with diameters ranging from 66 to 170 μm, truncated oblong in girdle view with the submarginal processes protruding ( Fig. 3. A). The green-brown chloroplasts are discoid, numerous and large, 5.5-9.0 μm in diameter ( Fig. 2. D). The valves present a flat central surface, rising at the submarginal processes and concave between them ( Fig. 3. F-J). The labiate processes are normally four ( Fig. 3. B, F-G), occasionally five ( Fig. 3. I-J; Fig. 4. F), and rarely ...
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... in outline with diameters ranging from 66 to 170 μm, truncated oblong in girdle view with the submarginal processes protruding ( Fig. 3. A). The green-brown chloroplasts are discoid, numerous and large, 5.5-9.0 μm in diameter ( Fig. 2. D). The valves present a flat central surface, rising at the submarginal processes and concave between them ( Fig. 3. F-J). The labiate processes are normally four ( Fig. 3. B, F-G), occasionally five ( Fig. 3. I-J; Fig. 4. F), and rarely six ( Fig. 3. C, H; see comment in Discussion, third paragraph), expanded into large hyaline hood-like structures (Fig. 3. A). Valves are strongly areolated, arranged in radial rows ( Fig. 3. I, K). The loculate ...
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... truncated oblong in girdle view with the submarginal processes protruding ( Fig. 3. A). The green-brown chloroplasts are discoid, numerous and large, 5.5-9.0 μm in diameter ( Fig. 2. D). The valves present a flat central surface, rising at the submarginal processes and concave between them ( Fig. 3. F-J). The labiate processes are normally four ( Fig. 3. B, F-G), occasionally five ( Fig. 3. I-J; Fig. 4. F), and rarely six ( Fig. 3. C, H; see comment in Discussion, third paragraph), expanded into large hyaline hood-like structures (Fig. 3. A). Valves are strongly areolated, arranged in radial rows ( Fig. 3. I, K). The loculate areolae are hexagonal, but those on the central area are ...
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... the submarginal processes protruding ( Fig. 3. A). The green-brown chloroplasts are discoid, numerous and large, 5.5-9.0 μm in diameter ( Fig. 2. D). The valves present a flat central surface, rising at the submarginal processes and concave between them ( Fig. 3. F-J). The labiate processes are normally four ( Fig. 3. B, F-G), occasionally five ( Fig. 3. I-J; Fig. 4. F), and rarely six ( Fig. 3. C, H; see comment in Discussion, third paragraph), expanded into large hyaline hood-like structures (Fig. 3. A). Valves are strongly areolated, arranged in radial rows ( Fig. 3. I, K). The loculate areolae are hexagonal, but those on the central area are angular and larger; some areolae ...
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... 3. A). The green-brown chloroplasts are discoid, numerous and large, 5.5-9.0 μm in diameter ( Fig. 2. D). The valves present a flat central surface, rising at the submarginal processes and concave between them ( Fig. 3. F-J). The labiate processes are normally four ( Fig. 3. B, F-G), occasionally five ( Fig. 3. I-J; Fig. 4. F), and rarely six ( Fig. 3. C, H; see comment in Discussion, third paragraph), expanded into large hyaline hood-like structures (Fig. 3. A). Valves are strongly areolated, arranged in radial rows ( Fig. 3. I, K). The loculate areolae are hexagonal, but those on the central area are angular and larger; some areolae located at the hyaline rays are pentagonal (Fig. ...
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... The valves present a flat central surface, rising at the submarginal processes and concave between them ( Fig. 3. F-J). The labiate processes are normally four ( Fig. 3. B, F-G), occasionally five ( Fig. 3. I-J; Fig. 4. F), and rarely six ( Fig. 3. C, H; see comment in Discussion, third paragraph), expanded into large hyaline hood-like structures (Fig. 3. A). Valves are strongly areolated, arranged in radial rows ( Fig. 3. I, K). The loculate areolae are hexagonal, but those on the central area are angular and larger; some areolae located at the hyaline rays are pentagonal (Fig. 3. K). Areolae number five in 10 μm at the center, being barely denser towards the margin, six to seven in 10 ...
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... and concave between them ( Fig. 3. F-J). The labiate processes are normally four ( Fig. 3. B, F-G), occasionally five ( Fig. 3. I-J; Fig. 4. F), and rarely six ( Fig. 3. C, H; see comment in Discussion, third paragraph), expanded into large hyaline hood-like structures (Fig. 3. A). Valves are strongly areolated, arranged in radial rows ( Fig. 3. I, K). The loculate areolae are hexagonal, but those on the central area are angular and larger; some areolae located at the hyaline rays are pentagonal (Fig. 3. K). Areolae number five in 10 μm at the center, being barely denser towards the margin, six to seven in 10 μm. A central rosette (5.7-9.0 μm in diameter), without a hyaline ...
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... six ( Fig. 3. C, H; see comment in Discussion, third paragraph), expanded into large hyaline hood-like structures (Fig. 3. A). Valves are strongly areolated, arranged in radial rows ( Fig. 3. I, K). The loculate areolae are hexagonal, but those on the central area are angular and larger; some areolae located at the hyaline rays are pentagonal (Fig. 3. K). Areolae number five in 10 μm at the center, being barely denser towards the margin, six to seven in 10 μm. A central rosette (5.7-9.0 μm in diameter), without a hyaline area, is present in all observed external valves ( Fig. 3. I, K). The outer velum of each areola has pores arranged in more or less parallel lines and lacks a raised ...
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... but those on the central area are angular and larger; some areolae located at the hyaline rays are pentagonal (Fig. 3. K). Areolae number five in 10 μm at the center, being barely denser towards the margin, six to seven in 10 μm. A central rosette (5.7-9.0 μm in diameter), without a hyaline area, is present in all observed external valves ( Fig. 3. I, K). The outer velum of each areola has pores arranged in more or less parallel lines and lacks a raised central papilla (Fig. 3. L-M). However, two to seven small papillae are present on the external marginal walls of each areola (Fig. 3. M). The foramina are internal, large (Fig. 4. C, D) with an eccentric location in the central ...
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... number five in 10 μm at the center, being barely denser towards the margin, six to seven in 10 μm. A central rosette (5.7-9.0 μm in diameter), without a hyaline area, is present in all observed external valves ( Fig. 3. I, K). The outer velum of each areola has pores arranged in more or less parallel lines and lacks a raised central papilla (Fig. 3. L-M). However, two to seven small papillae are present on the external marginal walls of each areola (Fig. 3. M). The foramina are internal, large (Fig. 4. C, D) with an eccentric location in the central areolae, and in those areolae bordering the hyaline rays, lying in the internal side of the valves between the center and the processes ...
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... rosette (5.7-9.0 μm in diameter), without a hyaline area, is present in all observed external valves ( Fig. 3. I, K). The outer velum of each areola has pores arranged in more or less parallel lines and lacks a raised central papilla (Fig. 3. L-M). However, two to seven small papillae are present on the external marginal walls of each areola (Fig. 3. M). The foramina are internal, large (Fig. 4. C, D) with an eccentric location in the central areolae, and in those areolae bordering the hyaline rays, lying in the internal side of the valves between the center and the processes (Fig. 3. K). The external surface of each labiate process consists of a domed hood with three slits suggesting ...
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... (Fig. 3. L-M). However, two to seven small papillae are present on the external marginal walls of each areola (Fig. 3. M). The foramina are internal, large (Fig. 4. C, D) with an eccentric location in the central areolae, and in those areolae bordering the hyaline rays, lying in the internal side of the valves between the center and the processes (Fig. 3. K). The external surface of each labiate process consists of a domed hood with three slits suggesting a trident (Fig. 4. B). Internally, and attached to the top of each submarginal valve cavity, appears a raised double horse-shoe-shaped structure of the labiate process ( Fig. 4. C). Each cingulum is composed of five to six non- perforated ...
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... specimens of A. kittonii agree well with those described by Holmes & Mahood (1980), Sims & Holmes (1983) and Tiffany (2008). The number of labiate processes on each cell is a variable feature. With light microscopy, we observed normally valves with four, five, and six processes, and rarely, cells with eight or ten processes were also found (Fig. 3. D-E). As valves with those characteristics had not been found in our previous SEM observations of the same samples, clean material dried on cover glasses at room temperature was observed under a light microscope and valves with eight or ten processes were encircled with an special diamond objective. Their observation with scanning ...
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... on the valve face. They are regularly 5 in 10 μm on each striae at the central part, but those areolae, bordering the hyaline rays were wider and pentagonal in shape. This feature, and the fact that these areolae also have the internal foramina in an eccentric location, makes the hyaline rays very notorious when observed by light microscopy (Fig. 3. C-E). This is the first record of Aulacodiscus kittonii as a recent and dominant "surf-diatom" species from the northern coast of Chile in the South Eastern Pacific Ocean. Accumulations of A. kittonii as the dominant species have until now only been reported from New Zealand, Brazil and the coast of Washington (Odebrecht et al. ...
Citations
... Aulacodiscus kittoni fue la especie registrada en todos los meses; se presenta generalmente en la rompiente de olas conformando un grupo reducido de especies que generan intensas acumulaciones sobre playas arenosas con oleaje fuerte. A menudo, son las únicas dominantes de la comunidad, se unen a las burbujas generadas por el oleaje y forman masas flotantes color marrón o verde, con forma irregular, que con la marea se depositan en la playa en franjas largas ( Fig. 4) (Cox, 1885;Rivera et al., 2016). ...
... It generally occurs in the surf zone and forms a small group of species producing massive accumulations on sandy beaches with strong waves. They are often the only dominant species in the community and join the bubbles generated by the waves forming floating brown or green masses of irregular shape, which are then deposited on the beach in long strips with the tide (Fig. 4) (Cox, 1885;Rivera et al., 2016). Dissolved oxygen is one of the most important water quality parameters for the health of phytoplankton because it influences several biogeochemical processes, such as respiration and metabolism impacting their life (Iriarte et al., 2015). ...
Durante los años de estudio (2017-2019), la comunidad fitoplanctónica estuvo constituida por 81 taxones y el grupo de las diatomeas fue el más representativo. Se observó dominancia fitoplanctónica de 79,97% y volumen promedio de 0,81 mL/100 L de agua filtrada. La densidad celular total fluctuó entre 0,01 y 1,59 cel.L-1. De las especies más abundantes, resaltó Aulacodiscus kittoni cuya concentración fue de 0,17 x 103 cel. L-1, diatomea propia de orilla que forma extensas franjas verdes en la costa de Camaná. La temperatura superficial del mar, estuvo entre los rangos 14,4 - 19,4 °C con promedio de 16,81 °C. La salinidad tuvo promedio de 34,93 ups, el oxígeno disuelto promedio fue de 6,12 mL/L y el pH estuvo en los rangos 7,53 - 8,09. Las concentraciones promedio de nutrientes coincidieron con los rangos promedio superficiales normales para la costa peruana (2,62 μM de fosfatos; 20,50 μM de silicatos; 0,72 μM de nitritos y 18,13 μM de nitratos). Las concentraciones de oxígeno alcanzaron el índice más alto de correlación positiva con la densidad celular promedio de fitoplancton.
Models for how diatoms move were devised as early as 1753 and up to the present. Most of them have not been pursued to the point of proof or disproof. Elements of some of the oldest models, fanciful and disputed, still help in thinking about this unsolved problem, which has been tackled by a wide variety of scientists, amateur and professional. The current models are full of holes, and are not based on modern understandings of secretory mechanisms, cytoplasmic streaming, and physical chemistry. A testable working model is presented, which is an amalgam of old and new. In this model, the major component of the raphe fluid is a polysaccharide designated as “raphan” which is synthesized by a membrane protein “raphan synthase,” either in Golgi vesicles called crystalloid bodies or in the cell membrane. The raphan synthase is transported to each raphe via cytoplasmic streaming engendered by its pair of adjacent microfilament bundles and attached myosin motor molecules, hydrodynamically inducing motion of the whole fluid cell membrane. The raphan is initially hydrophobic and fills the hydrophobic raphe, which is a capillary nanochannel. Proteins in the raphe fluid trigger hydration of the raphan on contact with a substrate. The hydrated raphan can no longer wet the raphe and exits, producing the diatom trail. The capillary force generated is sufficient to explain the force that a moving diatom can exert, whereas cytoplasmic streaming is 10,000 times weaker. The cytoplasmic streaming controls the direction of the diatom, whereas capillarity provides the force. Capillary motion is sustained by hydration of the raphan. By analogy with an automobile, the steering wheel requires a small force, which controls an engine that produces a much larger force. What turns the steering wheel or determines the direction of the cytoplasmic streaming is a higher order problem of behavior.
