Acus 5t
Adimar Poynter
Valves are narrow and lanceolate. The apices are protracted, narrowly attenuate, and mostly sub-rostrate to sub-capitate. The sternum is lanceolate, distinguishable under LM, and ranges in shape from linear to slightly expanded near the central area. The parallel striae are coarse, mostly occurring opposite or occasionally alternate. Rimoportula are present at the apices. Striae along the margin of central area may be reduced or absent, with ghost striae often present.
There has been much confusion regarding the identity of this taxon that can be attributed to the lack of original type material, line drawings and a suite of similar needle-like taxa. Lange-Bertalot and Ulrich (2014) designated a neotype for Ulnaria acus based on Ktzing material from Falaise, France (no. 401, BM 18305).
Ulnaria acus as presented on this page increases the length range reported by Lange-Bertalot and Ulrich (2014). We do not find North American specimens that are lacking a central area with ghost striae, as in the neotype population (Lange-Bertalot and Ulrich 2014; Pl. 25, Figs 2, 3). Also note that Lange-Bertalot and Ulrich (2014) used Fragilaria grunowii to describe larger specimens that have very narrowly attenuate apices. Our specimens of U. acus overlap in length range with F. grunowii, but we consider U. acus to have attenuate apices.
Patrick and Reimer (1966) observed this taxon (as Synedra acus) widely distributed across the United States in circumneutral rivers with moderate conductivity and hardness. Ulnaria acus is found in epilithic and epiphytic biofilms in moderately alkaline, oligosaprobic, and eutrophic freshwater streams and lakes (Lange-Bertalot and Ulrich 2014).
The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Ulnaria acus from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:
Ultrastructural changes induced by exposure to excess of organic matter were studied in Lepocinclis acus (ex Euglena acus). The cells isolated from the Matanza River, Buenos Aires, Argentina, were grown in soil water medium (SWM). When transferred to medium enriched with Bacteriological Peptone OXOID, marked body deformation and a significant shortening and widening of the cells was observed. These changes were unexpected in a species with quite rigid cells, a condition previously shown in studies of the pellicle fine structure. Transmission electron microscopy observations suggest that cellular deformation might be facilitated by an increase in strip number, whereas in the original strips normal ultrastructure was maintained. An increase in number and volume of paramylon grains and vacuoles, as well as the presence of membrane whorls in vacuoles was observed. The fine structure of organisms grown in medium with and without organic matter enrichment was compared, and the systematic and ecological importance of morphological changes triggered by cell deformation was discussed.
Copyright 2017 Conforti, Ruiz and Leonardi. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
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High-throughput method of sequencing was applied to determine the complete nucleotide sequence of an araphid pennate diatom Synedra acus subsp. radians from Lake Baikal (East Siberia). The assembled genome has a total length of 98 Mbp, the mean coverage is 33x. Structure-functional annotation of the genome was performed.
An acus is a Roman pin originally designed to secure a hairstyle (acus crinalis). They measure 6 to 9 inches in length and are made of gold, silver, bone, wood, or ivory. These handy long pins could also be used with or without a fibula pin to secure a garment.
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