Showing papers by "Matt P. Ashworth published in 2019"

Six new epibiotic Proschkinia (Bacillariophyta) species and new insights into the genus phylogeny

Abstract: The diatom genus Proschkinia is a common element of biofilms covering diverse substrata in saline inland or shallow coastal environments. It can be distinguished from other naviculoid taxa by its l...

Extreme diversity in fine-grained morphology reveals fourteen new species of conopeate Nitzschia (Bacillariophyta: Bacillariales)

Abstract: A study was made of the ultrastructural variation in a group of conopeate Nitzschia species, primarily marine species from Guam but also including one freshwater species from Costa Rica. Fourteen new species are described: Nitzschia alcyoneae, Nitzschia asteropeae, Nitzschia carahii, Nitzschia celaenoae, Nitzschia dagmannii, Nitzschia electrae, Nitzschia guamensis, Nitzschia jordanii, Nitzschia lascrucensis, Nitzschia maiae, Nitzschia meropeae, Nitzschia schefterae, Nitzschia spathulatoides, and Nitzschia taygeteae . The valves in all these taxa had a central raphe-sternum on a raised keel; from the keel arise silica flaps, the conopea, and the valve face was depressed below the conopea to form conopeal canals. The valve surface was thus differentiated into three regions, in which the areola pattern sometimes differed: the exposed valve face, the valve depression, and the peri-raphe zone, i.e., the exposed part of the keel wall between the conopeum and the raphe-sternum. We refer to this suite of characters as the tholophora (canopy-bearing) morphology. In one species, N. maiae sp. nov. , the conopea occurred only at the apex and there was no valve depression. Thirty-eight morphological characters were used in addition to the usual morphometric data (length, width, densities of striae and fibulae); these included, inter alia, a remarkable range of areola shapes on the three valve regions and the copulae—oval/circular pores, transapical slits, longitudinal slits, small pores fields, continuous pores fields, and larger quadrate pores closed by hymenes or cribra; the extent of the conopea along the valve; the presence of longitudinal ribs on the valve, conopea, or copulae; and the extent of internal development of silica below the striae. Phylogenetic analysis of gene sequences from six species was entirely congruent with analysis of morphological characters.

Toward a multigene phylogeny of the Cymatosiraceae (Bacillariophyta, Mediophyceae) II: morphological and molecular insights into the taxonomy of the forgotten species Campylosira africana and of Extubocellulus, with a description of two new taxa

Abstract: New molecular and morphological insights are presented on Campylosira africana and two new species, Extubocellulus cupola sp. nov. and Plagiogrammopsis castigatus sp. nov. Species descriptions were based on LM/SEM micrographs and a data set with concatenated sequences of SSU, rbcL and psbC loci constructed from 56 cymatosiroid strains isolated from global geographic locations. Extubocellulus cupola is distinguished by a mesh-like marginal ridge and dome-shaped areolation, and P. castigatus, by a prominent marginal extension at the valve center. Campylosira africana, a species from South Africa described by Professor Malcolm Giffen, has never been documented through LM or SEM, which led some authors to place it in synonymy under Campylosira cymbelliformis. We confirm that C. africana is a distinct species and provide microphotographic documentation and DNA sequences. We present morphological evidence for the well-known cymatosiroid species Extubocellulus spinifer possessing complete pili, and we emend the generic description of Extubocellulus.

Taxonomy and diversity of a little-known diatom genus Simonsenia (Bacillariaceae) in the marine littoral: novel taxa from the Yellow Sea and the Gulf of Mexico

Abstract: Background and aims – The diatom genus Simonsenia has been considered for some time a minor taxon, limited in its distribution to fresh and slightly brackish waters. Recently, knowledge of its diversity and geographic distribution has been enhanced with new species described from brackish-marine waters of the southern Iberian Peninsula and from inland freshwaters of South China, and here we report novel Simonsenia from fully marine waters. Methods – New isolates of Simonsenia species were obtained from marine waters, the littoral zone of the Korean Yellow Sea coast and the Gulf of Mexico in Corpus Christi (Texas), and documented in LM, SEM and with DNA sequence data (plastid-encoded rbcL and psbC). Phylogenetic trees of raphid diatoms were constructed to assess the relationships of the new species and of the genus as a whole. Key results and conclusions – Two novel species of Simonsenia (S. eileencoxiae and S. paucistriata) are described and a further putative taxon is characterized morphologically. The molecular phylogeny of the new Simonsenia species and previously sequenced species supports both the monophyly of the genus and its place within the Bacillariaceae. The Simonsenia clade clusters with clades composed of Cylindrotheca, Denticula and some Nitzschia spp. (including N. amphibia, N. frustulum, N. inconspicua). Hence Simonsenia is firmly positioned within the Bacillariaceae by molecular phylogenies, confirming its position within this group based on the possession of a canal raphe and its ultrastructure, and rejecting its classification within the Surirellaceae. Morphological data from the new Simonsenia species is typical for the genus, with a “simonsenioid” canal raphe type supported over the valve face with fenestral braces, alar canals connecting the canal raphe with the cell lumen, and the presence of fenestrae between the alar canals externally. Our results indicate unequivocally that the biogeography and the biodiversity of Simonsenia remain highly underestimated.

Polyphyly and homoplasic structures in rhizosolenioid diatom genera: a review

Abstract: Background and aims – Traditionally, extant rhizosolenioid diatom genera have been placed in a single family, the Rhizosoleniaceae. However, preliminary molecular data suggested that the family might be polyphyletic. Therefore, a literature review of the morphological, ultrastructural and molecular data of the rhizosolenioid genera was undertaken. Methods – In addition to the literature survey, the location of the rimoportula in a number of rhizosolenioid genera was investigated by breaking the valves and observing the fragments in the scanning electron microscope. Key results – The data provides strong support for the previous separation of Proboscia and Rhizosolenia at the family level (Probosciaceae vs. Rhizosoleniaceae), with the rimoportula being located at the tip of the proboscis in Proboscia, or with an internal labia at the base of the hollow tubular rimoportula (= spine or process) in Rhizosolenia and Pseudosolenia. Conclusions – The data suggests that a number of rhizosolenioid genera should be transferred to other families, and that gene sequences of two genera (Dactyliosolen and Neocalyptrella) are needed as their morphological features differ markedly from those of the Rhizosoleniceae s. str. (Rhizosolenia, Guinardia, Pseudosolenia).