Patrones de utilización del espacio en briozoos epibiontes de la vieira patagónica Psychrochlamys patagonica

We studied the bryozoan assemblage encrusting valves of the Patagonian scallop, Psychrochlamys patagonica, in 4 beds distributed along the continental shelf off Argentina to analyse (a) the distribution pattern of bryozoan colonies in different zones of the valves, (b) the influence of interspecific competition on assemblage composition, (c) whether encrusting species display different space utilisation strategies, and (d) whether bryozoan species richness and number of colonies vary in relation to host size. The assemblage was composed of 22 taxa and was dominated by Arachnopusia monoceros and Osthimosia eatonensis, which were at least one order of magnitude more abundant than any other species. Multivariate analyses based on coverage data of multiserial bryozoans separated the beds according to species richness rather than to geographic proximity and showed significant differences in assemblage structure between upper (left) and lower (right) valves and among beds. Competitive interactions occurred almost exclusively on lower valves, and more frequently in peripheral zones than in central zones of these valves. Correlations between valve area and number of bryozoan colonies, coverage and species richness were low but significant. Bryozoans were significantly more frequent, larger, and taxonomically diverse on lower valves than on upper valves. The uniserial colonies of Neothoa cf. chiloensis, the weakest bryozoan competitor, were as frequent in central zones as they were in peripheral zones, and usually spread out along channels on the scallop surface. This fugitive species was partially covered by multiserial colonies, but managed to persist even in peripheral areas of the lower valves.Se estudiaron los briozoos que incrustan las valvas de Psychrochlamys patagonica en 4 bancos de la plataforma continental argentina para analizar su distribución sobre distintas zonas de las valvas, la influencia de la competencia interespecífica sobre la composición de la asociación, si las especies incrustantes exhiben distintas estrategias de utilización del espacio y si la riqueza específica y abundancia varían en relación al tamaño del huesped. Entre los 22 taxa presentes, Arachnopusia monoceros y Osthimosia eatonensis fueron al menos un orden de magnitud más abundantes que las demás especies. Análisis multivariantes basados en datos de cobertura de briozoos multiseriales separaron a los bancos por su riqueza específica más que por su proximidad geográfica y demostraron diferencias significativas en la estructura de las asociaciones entre valvas superiores (izquierdas) e inferiores (derechas) y entre bancos. Las interacciones competitivas ocurrieron casi exclusivamente sobre valvas inferiores y más frecuentemente en la periferia que en el centro. Las correlaciones entre el área de las valvas y el número de colonias, cobertura y riqueza específica de briozoos fueron bajas pero significativas. Los briozoos fueron más frecuentes, más grandes y más diversificados en las valvas inferiores que en las superiores. Las colonias uniseriales de Neothoa cf. chiloensis, el competidor más débil, fueron tan frecuentes en la zona central como en la periferia, extendiéndose a lo largo de los canales en la superficie de las valvas. Esta especie fugitiva resulta parcialmente cubierta por los briozoos multiseriales, pero logra persistir hasta en la periferia de las valvas inferiores

Two new species and a new genus of Calloporidae (Bryozoa: Cheilostomata) from the Southwest Atlantic

The family Calloporidae occupies a basal position in the classification of the Cheilostomata, the relatively simple callop- orid morphology seeming to be the basic pattern for the adaptive radiation of cheilostome bryozoans. The ovicells of the Calloporidae may be formed by the maternal zooid or the distal zooid, which can be an autozooid, a vicarious avicularium or a kenozooid. Examination of new calloporid material from the southern Patagonian shelf revealed the existence of two new species and a new genus. Kenoaplousina fissurata gen. nov., sp. nov. is characterized by its distinctive kenozooidal ooecium. The new genus is also deemed to include Aplousina grandipora Moyano, an allied species from the Chilean con- tinental slope. Alderina simplicissima sp. nov., is also described from the Magellanic region.Fil: López Gappa, Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Liuzzi, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentin

Un nuevo género y especie de Chaperiidae (Bryozoa: Cheilostomata) del Mioceno temprano de Patagonia (Argentina)

La familia Chaperiidae alcanza su máxima biodiversidad en el hemisferio sur. El principal rasgo morfológico que caracteriza a la familia es un par de láminas calcáreas asociadas con la inserción de los músculos oclusores del opérculo. El propósito de este trabajo es describir a Aluis spinettai gen. et sp. nov., a partir de material obtenido en las Formaciones Monte León, Chenque y Puesto del Museo (Mioceno temprano, Patagonia, Argentina). A. spinettai posee colonias erectas bilaminares, suturas crenuladas entre los zooides, un extenso criptocisto y ovicelas esféricas, y carece de gimnocisto, espinas orales y avicularias. La nueva especie exhibe una notable convergencia morfológica con una especie del género Aspidostoma del Mioceno temprano (Fm. Chenque) en Patagonia. En algunas zonas de la colonia los zooides presentaban perforaciones circulares en el criptocisto realizadas por un depredador desconocido. A. spinettai presenta una distribución estratigráfica que va desde ~19 a 17 Ma (Burdigaliano). Su presencia sugiere una correlación entre los niveles superiores de la Formación Monte León y los inferiores de la Formación Chenque. La distribución paleogeográfica de esta nueva especie abarca al menos 500 km a lo largo de la costa atlántica austral de Sudamérica. Los representantes actuales de la familia Chaperiidae en el Atlántico Sudoccidental no parecen relacionados con A. spinetta.The family Chaperiidae reaches its highest biodiversity in the southern hemisphere. The main morphological feature characterizing the family is a pair of calcareous laminar structures associated with the insertion of the operculum occlusor muscles. The aim of this study is to describe Aluis spinettai gen. et sp. nov., from material collected in the Monte León, the Chenque, and the Puesto del Museo formations (early Miocene, Patagonia, Argentina). A. spinettai has erect bilaminar colonies, crenulated sutures between zooids, an extensive cryptocyst and spherical ovicells; gymnocyst, oral spines, and avicularia are absent. The new species exhibits a remarkable morphological convergence with a species of Aspidostoma from the early Miocene (Chenque Formation) of Patagonia. In some areas of the colony, the cryptocysts were pierced by circular drill holes made by an unknown predator. The stratigraphic distribution of A. spinettai ranges from â19 to 17 Ma (Burdigalian). Its presence suggests a correlation between the upper levels of the Monte León Formation and the lower levels of the Chenque Formation. The paleogeographic distribution of this new species spans at least 500 km along the southern Atlantic coast of South America. The living representatives of the Chaperiidae in the Southwest Atlantic do not seem related to A. spinettai.Fil: López Gappa, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Pérez, Leandro Martín. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Checklist of the marine Bryozoa from Uruguay (Southwest Atlantic)

El conocimiento de la fauna marina de briozoos de Uruguay se basa principalmente en registros dispersos que se encuentran en estudios faunísticos locales y en los resultados taxonómicos de dos cruceros oceanográficos en el Atlántico sudoccidental, pero aún no se ha publicado un estudio exhaustivo para esta área. Este trabajo tiene como objetivo compilar una lista actualizada, que reúna toda la información publicada sobre la fauna de briozoos uruguayos. De los 73 taxones registrados, 30 (41%) solo se conocen de aguas profundas frente al Río de la Plata. Incluso considerando las especies que no han sido determinadas, el resultado muestra un alto grado de endemismo, como el ya demostrado para varios grupos bentónicos como Bivalvia, Ascidiacea y Pycnogonida. La ausencia de taxónomos locales de briozoos ha resultado en una situación sin precedentes, donde la fauna de briozoos de aguas profundas de Uruguay es más conocida que la de ambientes costeros y de plataforma. La principal conclusión de esta recopilación de la fauna de briozoos es que se deben realizar esfuerzos para coordinar la recolección y el estudio taxonómico de las colecciones de briozoos de zonas someras y de plataforma, para cerrar la brecha de conocimiento actual sobre la biodiversidad de este importante grupo de invertebrados marinos bentónicos.Knowledge of the marine bryozoan fauna of Uruguay is mostly based on scattered records found in local faunistic surveys and the taxonomic results of two oceanographic cruises to the Southwest Atlantic, but a comprehensive study has not yet been published for this area. This paper aims to compile an updated checklist, bringing together all the published information about the Uruguayan bryozoan fauna. Of the 73 recorded taxa, 30 (41%) are known only from deep waters off the Río de la Plata. Even considering undetermined species, these results show the high degree of endemism as it was already shown for several other benthic groups such as Bivalvia, Ascidiacea and Pycnogonida. The absence of local taxonomists on bryozoans has resulted in the unprecedented situation that the deep-sea bryozoan fauna of Uruguay is better known than the coastal and shelf representatives of the phylum. The main conclusion of this faunal compilation is that efforts should be made to coordinate the gathering and taxonomic study of shallow and shelf bryozoan collections to bridge the present knowledge gap about the biodiversity of this important group of marine benthic invertebrates.Fil: Vieira Ramalho, Laís. Universidade Federal Do Rio de Janeiro. Museu Nacional; BrasilFil: López Gappa, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Scarabino, Fabrizio. Ministerio de Educación y Cultura. Museo Nacional de Historia Natural; Urugua

First record of a fossil selenariid bryozoan in South America

Selenariidae Busk 1854 (Bryozoa) is considered endemic to Australia and New Zealand. Here we describe a new species of Selenaria Busk 1854 from the lower Miocene Monte León Formation (Patagonia, Argentina). Selenaria lyrulata sp. nov. is characterized by autozooids with a lyrula-like, anvil-shaped cryptocystal denticle, opesiular indentations and lateral condyles, as well as avicularia with a shield of fused costae. This is the first record of a selenariid bryozoan in South America.Facultad de Ciencias Naturales y Muse

SPECIES OF THE GENUS MELICERITA MILNE EDWARDS (BRYOZOA, CHEILOSTOMATIDA) IN THE EARLY MIOCENE OF PATAGONIA (ARGENTINA)

Species of the cellariid genus Melicerita Milne Edwards develop bilaminar flattened colonies consisting of alternate transverse rows of hexagonal zooids. In South America, its stratigraphic range extends from the early Miocene to the Recent. Re-examination of the type material of M. triforis Ortmann from the Monte León Formation at Río Chalía, and scanning electron microscope images of M. ortmanni Canu from the early Miocene Chenque Formation, confirmed that the latter is a junior synonym of M. triforis. Vicarious avicularia are described for the first time in M. triforis. Lectotypes are herein chosen for both nominal species. M. imperforata sp. nov. is described from material obtained in Monte León Formation (early Miocene). It differs from all known Melicerita species in the size and shape of its vicarious avicularia, which are marginal and much larger than the autozooids. The Recent Magellanic species M. temaukeli Moyano and M. blancoae López Gappa share morphological similarities with M. triforis

First record of a fossil selenariid bryozoan in South America

Selenariidae Busk 1854 (Bryozoa) is considered endemic to Australia and New Zealand. Here we describe a new species of Selenaria Busk 1854 from the lower Miocene Monte León Formation (Patagonia, Argentina). Selenaria lyrulata sp. nov. is characterized by autozooids with a lyrula-like, anvil-shaped cryptocystal denticle, opesiular indentations and lateral condyles, as well as avicularia with a shield of fused costae. This is the first record of a selenariid bryozoan in South America.Facultad de Ciencias Naturales y Muse

Bryozoa

El phylum de los briozoos posee actualmente más de 5000 especies, en su inmensa mayoría marinas, que suelen vivir en epibiosis sobre algas, o incrustando diversos sustratos duros como piedras, valvas de moluscos, caparazones de crustáceos, etc. Su existencia abarca desde el Ordovícico Temprano hasta la actualidad, estimándose que la biodiversidad del conjunto de las faunas fósiles es alrededor del cuádruple de las recientes. A pesar de la importancia de estas cifras, los briozoos no son muy conocidos a nivel popular, quizás debido a su pequeño tamaño. Los primeros naturalistas los clasificaron junto con los hidrozoos en el grupo de los zoófitos, dudando incluso de su naturaleza animal. Estudios posteriores revelaron que los briozoos poseen un nivel de organización superior al de los hidrozoos, presentando un verdadero celoma y tubo digestivo completo. El nombre con que debía designarse a estos invertebrados motivó interminables discusiones. Fueron llamados Polyzoa por los autores británicos y Ectoprocta por los norteamericanos. El término Bryozoa, utilizado inicialmente en Europa continental, ahora es aceptado por casi todos los especialistas.Facultad de Ciencias Naturales y Muse

No longer the pristine confines of the world ocean: a survey of exotic marine species in the southwestern Atlantic

We conducted a comprehensive survey of existing knowledge about exotic marine organisms introduced to the southwestern Atlantic Ocean, including coastal and shelf areas of Uruguay and Argentina. This domain is equivalent to the so-called Patagonian Shelf Large Marine Ecosystem, and corresponds to two biogeographic provinces: warm-temperate (Argentine Province) and cold temperate (Magellanic Province). The search included species that can be confidently categorized as introduced (31) and cryptogenic species (46). We present a comprehensive picture of recorded introductions (the first for this region) and some prominent ecological consequences. Most coastal ecosystems between the La Plata River estuary and central Patagonia have already been modified, or are expected to be so in the short term. Five recent, human-mediated biological invasions have already had a significant ecological impact. A barnacle (Balanus glandula) belt has developed on all rocky shores where none was present 30 years ago, a macro-fouler (Limnoperna fortunei) and a reef-builder (Ficopomatus enigmaticus) have strongly modified estuarine ecosystems, Pacific oyster (Crassostrea gigas) reefs are expanding in shallow bays at a fast rate, and kelp (Undaria pinnatifida) is rapidly modifying nearshore benthic communities along the coasts of central Patagonia. At this point, it is uncertain how many of the cordgrasses (Spartina spp.) found in coastal salt marshes correspond to exotic forms. Only exposed sandy beaches appear to be free from the pervasive ecological impact of invasion by exotic species. Poor knowledge of the regional biota makes it difficult to track invasions.Facultad de Ciencias Naturales y Muse

Morphometric diversity of the pulmonate limpet Siphonaria lessoni in different coastal environments

Siphonaria lessoni (Blainville, 1824) is the most abundant marine gastropod in the rocky intertidal zone of Buenos Aires Province, Argentina. The morphology of this species was studied in 6 sites near the city of Quequén, differing in intertidal height and degree of exposure to wave action and pollution. Shell length, width, height, and the distance from apex to posterior shell margin were measured, as well as the dry weight of both the shell and limpet body. A data matrix of 600 individuals (100 limpets per site) by 6 variables was analyzed by Principal Component Analysis (PCA) and Discriminant Analysis (DA) in order to compare size and shape differences among sites. As expected, axis I of the PCA explained a very high percentage (87.7%) of total variance, and can be interpreted as a size factor. Axis II, which summarised 6.9 %, may be regarded as expressing shell shape. Limpets not exposed to wave action within Quequén Harbour showed the highest values in all variables, whereas individuals living within the Brachidontes rodriguezi (d'Orbigny, 1846) community were very small and highly variable. Limpets heavily exposed to sewage at mid intertidal levels had a subcentral shell apex and were relatively very low. Classification of individuals by DA showed that the most characteristic morphology corresponded to limpets living at mid intertidal level close to a sewage outfall, or within Quequén Harbour (94 and 97 % correct reallocations, respectively). The influence of different physical and biotic factors on the morphology of Siphonaria lessoni is discussed.Fil: Tablado, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: López Gappa, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentin