Patricio Rivera

MORPHOLOGY AND TAXONOMY OF THREE VARIETIES OF COCCONEIS COSTATA AND C. PINNATA (BACILLARIOPHYCEAE) WITH CONSIDERATIONS OF PLEURONEIS

The frustule of Cocconeis costata var. costata, its varieties hexagona and pacifica, and C. pinnata (Bacillariophyceae), mainly collected in SE Pacific Ocean coastal and antarctic waters, have been studied. Ultrastructural information is provided for the first time for most of them. The taxa show several common features in relation with the low density and areolation of the striae (except for C. costata var. pacifica); broad and highly internally silicified interstriae; areola opening and arrangement, and location of the areola occlusion; type of valvocopula and absence of fimbriae in both valves, and presence of a transverse hyaline central area in the sternum valve (or araphid valve). Only the valvocopula of the sternum valve of C. costata var. pacifica displays fimbriae which are similar to the crenate edge of a leaf. Though only partially studied, the areola occlusion shows great uniformity on comparing both valves. The taxa differ with respect to the overall morphology and the areolar density of both...

MORPHOLOGY AND EVOLUTIONARY SIGNIFICANCE OF ADONEIS PACIFICA GEN. ET SP.NOV. (FRAGILARIACEAE, BACILLARIOPHYTA), A MARINE ARAPHID DIATOM FROM CHILE

A new marine diatom genus and species, Adoneis pacifica G.W. Andrews and P. Rivera, has been identified in Chilean coastal waters. This taxon shows obvious affinities to the genera Rhaphoneis and Delphineis, but cannot be classified in either, as they are currently construed. Adoneis pacifica resembles Rhaphoneis in outline and to some degree in the pseudocelli, whereas it resembles Delphineis in the structure of the vela and the positioning of the apical rimoportulae. However, distinctive characters of this new monotypic genus are: (1) the usual positioning of a single rimoportula near the centre of each lateral margin of the valve, and (2) the occurrence of well organized apical pore fields (pseudocelli), in which the pores are much smaller than elsewhere on the valve. These appear to be primitive traits for the araphid diatom family Fragilariaceae, and they suggest that Adoneis pacifica may be a conservative species important in the study of the evolution of the family.

DISTRIBUTION AND MORPHOMETRY ANALYSIS OF CYCLOSTEPHANOS ANDINUS COMB. NOV., A PLANKTONIC DIATOM FROM THE CENTRAL ANDES / Distribución y análisis morfométrico de la especie Cyclostephanos andinus comb. nov., una diatomea planctónica de los Andes centrales

The taxonomie position of Cyclotella andina Theriot, Carney et Richerson, a tropical freshwater planktonic diatom originally identified from Lake Titicaca, is modified based on morphological characters. The presence of striae arranged in discrete fascicles on the valve- face, coupled with the placing of fiilto- and rimoportulae on the same internal costa below the position of external spines (or on the valve face/mantle region in spineless individuals), form the basis to transfer this species from the genus Cyclotella Kützing to the genus Cyclostephanos Round. Morphometric analyses of 350 valves from seven populations from three Andean lakes demonstrate a morphological continuum in fossil and modern assemblages. Principal Component Analysis (PCA) shows that three main factors characterize most of the variability in morphology. PCI (λ1 = 71.7%) is a size-related component (e.g. valve diameter); PC2 (λ2 = 23.9%) is a size-free component that relates the length of biseriate to uniseriate areolae, and PC3 (λ3 = 1.73%) represents the ratio between the number and distance of biseriate or uniseriate areolae. We herein propose the taxonomie transfer of Cyclotella andina as Cyclostephanos andinus comb. nov.

Observations and comments on the diatom Stephanodiscus minutulus (Kützing) Cleve & Möller (Bacillariophyceae) found for the first time in Chile from bottom sediments collected in Lake Laja

En este estudio se senala la presencia de la diatomea Stephanodiscus minutulus (Kutzing) Cleve & Moller por primera vez para aguas continentales de Chile; es un taxon muy comun en diversos sistemas acuaticos de Europa y Norteamerica, y para Sudamerica solo existen escasos registros en Argentina. La especie fue encontrada en un perfl sedimentario colectado en el Lago Laja (Cordillera de los Andes), Chile central. Se describen las principales caracteristicas morfologicas de S. minutulus y se entregan comentarios sobre su relacion con otras especies cercanas.

Extubocellulus spinifer (Hargraves & Guillard) Hasle, Stosch & Syvertsen (Cymatosiraceae, Bacillariophyceae): First report of the species from the Southeastern Pacific with comments on the variability of some of its morphological features

Durante el analisis de cepas provenientes de muestras de fitoplancton marino se observo que una de ellas contenia celulas muy pequenas, aisladas o formando cortas cadenas de 2-4 individuos. Observaciones realizadas con microscopia electronica revelaron la presencia de Extubocellulus spinifer (Hargraves & Guillard) Hasle, Stosch & Syvertsen, una diminuta especie no senalada hasta ahora para el Pacifico Suroriental. En el presente trabajo se describen las caracteristicas de las celulas chilenas, se comenta acerca de la variabilidad de algunas de sus caracteristicas morfologicas, y se discute sobre las diferencias entre las dos especies conocidas del genero.

ACERCA DE LA DIATOMEA DIDYMOSPHENIA GEMINATA (LYNGBYE) M. SCHMIDT: SU MORFOLOGÍA Y DISTRIBUCIÓN EN CHILE

The freshwater diatom Didymosphenia geminata was studied from Chilean material collected in Rio Espolon and Rio Bio-Bio using light and electron microscopy. Its principal morphological features are described and illustrated for the first time and comments about its relationships with other closely taxa, as well as its distribution in Chile, are given.

LEPTOCYLINDRUS MINIMUS GRAN (BACILLARIOPHYCEAE): MORFOLOGIA Y DISTRIBUCION EN CHILE

Sobre la base de material recolectado en Calbuco, Chiloe, se confirma la presencia en Chile de Leptocylindrus minimus Gran (Bacillariophyceae)

La familia Hemiaulaceae (Bacillariophyceae) de las aguas marinas chilenas

The Family Hemiaulaceae comprises four genera, all of which have been previously reported for coastal waters off Chile, and represented by the following taxa: Cerataulina pelagica (Cleve) Hendey, Hemiaulus sinensis Greville, H. membranaceus Cleve, Climacodium biconcavum Cleve, Eucampia antarctica (Castracane) Mangin, E. cornuta (Cleve) Grunow and E. zodiacus Ehrenberg. However, examination with light and electron microscopy of marine samples from along the Chilean coast and the Antarctic Peninsula (including those used in earlier publications) revealed that (1) the genus Cerataulina is represented by C. pelagica, and is distributed along the Chilean coast between Arica in the north and the Magellan Strait in the south, (2) the genus Eucampia comprises four taxa: E. zodiacus f. cylindrocornis Syvertsen (previously reported for Chile as E. zodiacus f. zodiacus), E. zodiacus f. recta Rivera, Avaria & Cruces (described here), E. cornuta and E. antarctica. The former three taxa occur in the central and northern coast of Chile, while E. antarctica lives in Antarctic waters south of the Magellan Strait, (3) earlier records of Hemialus membranaceus, H. sinensis and Climacodium biconcavum in Chilean waters are misidentifications of Eucampia zodiacus f. recta f. nov. A short description is included for each taxon, and photographs provide information about the main morphological characteristics.

Spicaticribra kingstonii Johansen, Kociolek & Lowe (Thalassiosirales, Bacillariophyta): primera cita del género y de la especie para las aguas continentales de Chile

Spicaticribra kingstonii Johansen, Kociolek & Lowe fue hallada en aguas de la Laguna Grande de San Pedro, Chile. Esta es la primera cita del genero y de la especie para el pais. Los individuos chilenos carecen de una fultoportula central en la cara valvar, de tubos externos en las fultoportulae marginales y poseen areolas con cribra internas anastomosadas en forma de espiga, caracteristicas que concuerdan con las del genero Spicaticribra. En el presente trabajo se entrega una diagnosis con las caracteristicas relevantes de los individuos chilenos, se comenta la variabilidad de algunas de ellas, se menciona su relacion con taxones afines, y fotografias obtenidas mediante tecnicas de microscopia fotonica y electronica de barrido ilustran esos caracteres.

TRANSFER OF ACHNANTHES LOOSERI FRENGUELLI TO THE GENUS PLANOTHIDIUM

Se estudio el material tipo de Achnanthes looseri Frenguelli mediante tecnicas de microscopia fotonica y electronica de barrido. Se propone el traslado de la especie al genero Planothidium. Se designa el lectotipo y se entrega una diagnosis corregida del taxon.