Blastogeny in tabulate corals: case studies using X‐ray microtomography

X‐ray microtomography (XMT) is a non‐invasive and non‐destructive method that has often been used to study fossils. It allows serial sections to be made as little as few micrometers apart; such a resolution is unachievable for classical serial sectioning; moreover, in contrast to the latter, the specimen is not destroyed. Microtomography can, however, be applied only in cases where differences in X‐ray absorption between the skeleton and its infilling are great. We show that this method may be also applied to tabulate corals. Case studies of blastogeny are based on Silurian (Aulopora, Favosites) and Devonian (Thamnopora) specimens from Poland. We show that the sequence of events in the blastogeny of Aulopora sp. is different from that of ‘Aulopora serpens minor’ from the Devonian of the Holy Cross Mountains and similar to auloporids from the Devonian of England. Blastogeny in Favosites is very similar to that known from the related genera Squameofavosites and Thamnopora. This suggests that members of the genus Aulopora may be more diversified within the genus (as presently understood) than genera within the Favositidae.     

Dorlodotia and related genera (Rugosa) from the Visean (Mississippian; Carboniferous) of Zonguldak and Bartin (North‐Western Turkey)

Abstract: A rich and diverse coral fauna collected from the Livian (Viséan, Mississippian) of Zonguldak and Bart?n (North‐western Turkey) contains numerous specimens of Dorlodotia and related forms. The most common species, D. delepinei Charles, 1933 , is redetermined as Dorlodotia briarti, an European species. A new species of Dorlodotia is described for very large, phaceloid forms: D. euxinensis. The genus Ceriodotia is created for species close to Dorlodotia with a cerioid habit. It comprises two species: C. bartinensis and C. petalaxoides, both common in the Viséan of Zonguldak and Bart?n. Based on comparison of morphological characters and features of the astogeny, a phylogenetic lineage is proposed for Dorlodotia and the new taxa. The evolution of D. euxinensis from D. briarti is peramorphic. Subsequent paedomorphosis resulted in the lineage D. euxinensis–C. bartinensis–C. petalaxoides. Ceriodotia probably includes Viséan taxa from Asia previously described as ‘Acrocyathus’.     

A diverse chasmataspidid (Arthropoda: Chelicerata) fauna from the Early Devonian (Lochkovian) of Siberia

Examination of material held at the Palaeontological Institute, Moscow, enables the identification of two novel chasmataspidid species: Nahlyostaspis bergstroemi gen. et sp. nov. and Skrytyaspis andersoni gen. et sp. nov. ‘Eurypterus’ stoermeri and ‘Tylopterella’ menneri are both redescribed as chasmataspidids, having previously been assigned to Eurypterida. ‘T’. menneri is transferred to the new genus Dvulikiaspis gen. nov. An identical prosomal structure is identified in ‘Eurypterus’ stoermeri and Heteroaspis novojilovi from the Devonian of Germany and the two species are synonymized, with ‘E’ stoermeri having priority. The previous synonymy of H. novojilovi with Diploaspis casteri is rejected. The presence of ophthalmic ridges is confirmed within Diploaspididae, and new structural characteristics of their bucklers are identified.     

Specificity of fungal associations of Pyroleae and Monotropa hypopitys during germination and seedling development

Mycoheterotrophic plants obtain organic carbon from associated mycorrhizal fungi, fully or partially. Angiosperms with this form of nutrition possess exceptionally small ‘dust seeds’ which after germination develop ‘seedlings’ that remain subterranean for several years, fully dependent on fungi for supply of carbon. Mycoheterotrophs which as adults have photosynthesis thus develop from full to partial mycoheterotrophy, or autotrophy, during ontogeny. Mycoheterotrophic plants may represent a gradient of variation in a parasitism–mutualism continuum, both among and within species. Previous studies on plant–fungal associations in mycoheterotrophs have focused on either germination or the adult life stages of the plant. Much less is known about the fungal associations during development of the subterranean seedlings. We investigated germination and seedling development and the diversity of fungi associated with germinating seeds and subterranean seedlings (juveniles) in five Monotropoideae (Ericaceae) species, the full mycoheterotroph Monotropa hypopitys and the putatively partial mycoheterotrophs Pyrola chlorantha, P. rotundifolia, Moneses uniflora and Chimaphila umbellata. Seedlings retrieved from seed sowing experiments in the field were used to examine diversity of fungal associates, using pyrosequencing analysis of ITS2 region for fungal identification. The investigated species varied with regard to germination, seedling development and diversity of associated fungi during juvenile ontogeny. Results suggest that fungal host specificity increases during juvenile ontogeny, most pronounced in the fully mycoheterotrophic species, but a narrowing of fungal associates was found also in two partially mycoheterotrophic species. We suggest that variation in specificity of associated fungi during seedling ontogeny in mycoheterotrophs represents ongoing evolution along a parasitism–mutualism continuum.     

Schischcatella (Fenestrata,Bryozoa) from the Devonian of the Rhenish Massif,Germany

Abstract: The Devonian fenestrate bryozoan, Schischcatella Waschurova, 1964 , possessed colonies in the form of low, erect bifoliate fronds that grew from an encrusting sheet‐like base with autozooecia arranged in biserial, bifurcating rows. This growth habit is unique in fenestrates, which normally had unilaminate arborescent colonies. Originally, Schischcatella was described from the Lower Devonian of Tajikistan. This article describes a new species, S. heinorum sp. nov., from the Middle Devonian of the Eifel (western Rhenish Massif, Germany) with additional material from the Lower Devonian of the Kellerwald (eastern Rhenish Massif, Germany). External and internal morphologies of this bryozoan have been studied using abundant material. The growth habit of Schischcatella suggests a completely different pattern of feeding currents than that in the normal fenestrate colony. The outflow of the filtered water occurred only on edges of colonies between rami. In the absence of chimneys (areas of vertical water expelling), such a functional morphology may have restricted extension of the colony in a distal direction. The evolution of Schischcatella is apparently an example of paedomorphosis, the genus evolved from an unknown semicosciniid species by the early ontogenetic interruption of colony development and further changes in the mode of growth.     

New sea urchin phylogeography reveals latitudinal shifts associated with speciation

Where do new species arise? When do they form and how do they diverge from a common ancestor? A new comprehensive study of Arbacia sea urchins provides surprising answers to these questions. By combining mtDNA phylogeographic markers with a nuclear locus (encoding the sperm acrosomal protein bindin) known to be susceptible to high rates of adaptive codon evolution, Lessios et al. (2012) show that new species and lineages arose relatively recently, most often in association with latitudinal shifts between the temperate zones and the tropics, and in one case, in association with a significant geological barrier to gene flow (the rise of the Isthmus of Panama). In addition to the ‘where’ and ‘when’ of Arbacia speciation, these new data resolve an important question about ‘who’Arbacia species are by revealing extensive allele sharing at both loci between a pair of broadly sympatric nominal species (that should perhaps be considered a single taxon). ‘How’Arbacia diverge from each other is less easily resolved: there is no evidence for reinforcement (via selection on bindin) as an important source of divergence between nominal species, and there are few other data to decide among the alternative hypotheses to explain Arbacia speciation.     

Growth characteristics of Protoheliolites norvegicus (Tabulata; Upper Ordovician; Estonia)

Protoheliolites is an early heliolitine coral characterized by closely spaced corallites separated in places by sparse coenenchyme. Growth characteristics in the type species, P. norvegicus, are revealed by detailed analysis based on serial peels and thin sections of coralla from the uppermost Katian of north‐western Estonia. Colonies of this species had a strong ability to recover from damage and partial mortality, resulting in various forms of rejuvenation, regeneration, fusion and reorganization of corallites; in some cases, this involved relatively large areas of undifferentiated soft parts. The shells of commensal cornulitids became enclosed in host coralla during colony growth. Coralla of P. norvegicus exhibit distinctive growth cycles due to responses to seasonal changes. The production of new corallites by coenenchymal increase usually occurred in low‐density bands, in which corallites generally display round to subrounded transverse outlines. In high‐density bands, the corallites became crenulated, their wall thickness increased, septal development was more pronounced, and the amount of coenenchyme increased. In addition to these cyclomorphic changes, there were significant astogenetic changes during growth. Compared with the early stage of colony development, distinctive characteristics in the late astogenetic stage include a decrease in the growth rate of the colony, better coordination among corallites, maximum development of corallite crenulations and septa in high‐density bands, more numerous coenenchymal tubules and a greater proportion of corallum area occupied by coenenchyme. In general, the role of polyps in determining morphological characteristics of individual corallites, such as tabularium area, corallite crenulations and wall thickness, was subordinate to the astogeny of the colony. Growth characteristics including colony‐wide coordination of polyp behaviour and subjugation of individuals to restore the colony following damage suggest a strong astogenetic control and high level of colony integration. Protoheliolites probably arose from a heliolitine genus rather than from a nonheliolitine group as some authors have proposed.     

Iterative ontogenetic development of ammonoid conch shapes from the Devonian through to the Jurassic

We measured longitudinal growth in conch cross‐sections of 177 Devonian to Jurassic ammonoid species to test whether conch ontogenetic development parallels the iterative evolution of pachyconic or globular conch shapes. Ontogenetic trajectories of two cardinal conch parameters, conch width index and umbilical width index, show a few common recurring ontogenetic pathways in terms of the number of ontogenetic phases. The most common, with three phases in the conch width index (decrease–increase–decrease) and umbilical width index (increase–decrease–increase), is termed here C‐mode ontogeny (after the Carboniferous genus Cravenoceras). Many of the studied globular Palaeozoic and Triassic species (of the latter, particularly the arcestid ammonoids) share principal patterns in the triphasic C‐mode conch ontogeny in closely related groups but also between unrelated groups as well. The repetition of conch growth patterns is an example of convergent evolution of the entire life history of globular ammonoids. The studied Jurassic globular shaped ammonoids deviate from the growth patterns seen in earlier groups showing less pronounced ontogenetic trajectories with nearly isometric or weakly asymmetric growth without distinct phases. This trajectory is termed here M‐mode ontogeny (after the Jurassic genus Macrocephalites). No major change in the ontogenetic modes of pachyconic and globular ammonoids occurred moving from the Palaeozoic into the Mesozoic; the survivors of the end‐Permian extinction event iteratively developed conch ontogenies similar to those of Palaeozoic forms. In contrast, the Triassic–Jurassic boundary marks the major event with the evolution of some cardinal conch parameters relating to globular ammonoid ontogeny.     

The fate of the homoctenids (Tentaculitoidea) during the Frasnian–Famennian mass extinction (Late Devonian)

The homoctenids (Tentaculitoidea) are small, conical‐shelled marine animals that are among the most abundant and widespread of all Late Devonian fossils. They were a principal casualty of the Frasnian–Famennian (F‐F, Late Devonian) mass extinction, and thus provide an insight into the extinction dynamics. Despite their abundance during the Late Devonian, they have been largely neglected by extinction studies. A number of Frasnian–Famennian boundary sections have been studied, in Poland, Germany, France, and the USA. These sections have yielded homoctenids, which allow precise recognition of the timing of the mass extinction. It is clear that the homoctenids almost disappear from the fossil record during the latest Frasnian ‘Upper Kellwasser Event’. The coincident extinction of this pelagic group, and the widespread development of intense marine anoxia within the water column, provides a causal link between anoxia and the F‐F extinction. Most notable is the sudden demise of a group, which had been present in rock‐forming densities, during this anoxic event. One new species, belonging to Homoctenus is described, but is not formally named here.     

Dynamic body acceleration increases by 20% during flight ontogeny of greylag geese Anser anser

Despite our knowledge of the biophysical and behavioural changes during flight ontogeny in juvenile birds, little is known about the changes in the mechanical aspects of energy expenditure during early flight development, particularly in migratory species. Here, we investigate in a unique experimental setup how energy expended during flights changes over time beginning with early ontogeny. We calculate overall dynamic body acceleration (ODBA) as a proxy for energy expenditure in a group of hand raised greylag geese Anser anser trained to fly behind a microlight aircraft. We propose two potential hypotheses; energy expenditure either increases with increasing physiological suitability (the ‘physical development hypothesis’), or decreases as a result of behavioural improvements mitigating flight costs (the ‘behavioural development hypothesis’). There was a significant temporal increase of flight duration and ODBA over time, supporting the ‘physical development hypothesis’. This suggests that early on in flight ontogeny behavioural development leading to flight efficiency plays a weaker role in shaping ODBA changes than the increased physical ability to expend energy in flight. We discuss these findings and the implications of flight development on the life history of migratory species.     

Male aggression,limited female choice and the ontogeny of mating behaviour in the flesh fly Sarcophaga crassipalpis

Previous work has shown that male flesh flies (Sarcophaga crassipalpis Macquart) exhibit an ontogeny of behaviour from eclosion through sexual maturity that includes extensive changes in the expression of aggressive, non‐aggressive interactive and non‐interactive behaviours. To determine how the presence of a female flesh fly influences the manifestation of these behaviours, male flesh flies of different ages post‐eclosion are paired with same‐age females and their behaviours are monitored in a simple arena during a 50‐min observation period. All flies are socially isolated until pairing. Although the levels of expression of aggressive and non‐aggressive interactive behaviours are depressed relative to previous findings in male‐opponent pairs, the ontogeny of aggression still occurs as indicated by a significant increase, with age, in the agonistic behaviour ‘hold’. Similar to male‐opponent pairs and individual males, the performance by males of the non‐interactive behaviours ‘walking’ and ‘standing’ diminishes, whereas ‘upside‐down’ increases with age. By contrast, ‘grooming’ shows a significant age‐related decline. No courtship behaviours are observed in the males, although the aggressive behaviour ‘hold’ is a significant transition to mating. Females show no obvious courtship or rejection behaviours, although the significant increase in ‘upside‐down’ with age could possibly be a behavioural gateway to mating. The results of this study indicate that extensive age‐related changes encompassing the entire behavioural repertoire are intrinsic to male flesh flies and persist under a variety of different social contexts.     

The interrelationships of Devonian lungfishes (Sarcopterygii: Dipnoi) as inferred from neurocranial evidence and new data from the genus Soederberghia Lehman, 1959

New data are presented on the neurocranial complex (endocranium plus intimately associated bones of the palate) of the Late Devonian (Famennian) ‘rhynchodipterid’ lungfish Soederberghia groenlandica from the Aina Dal Formation (Celsius Bjerg Group) of East Greenland. Only the otic and occipital regions of the braincase are ossified in Soederberghia. The neurocranium of this genus shares a series of derived features with ‘Griphognathus’whitei, including a cranial centrum, fenestrate lateral cristae, and gutters on the ventral surface of the parasphenoid interpreted as accommodating the lateral dorsal aortae. The interrelationships of early lungfishes have been the subject of considerable disagreement. New data from Soederberghia are coupled with a data set focused on the character‐rich neurocranial complex in order to examine the systematic utility of this underexploited morphological system. Different methods of phylogenetic inference (maximum parsimony, Bayesian) return broadly consistent results. The Early to Middle Devonian forms Dipnorhynchus, Stomiahykus and Uranolophus are placed among the most basal of lungfishes. ‘Holodontids’ plus ‘rhynchodipterids’ (comprising Griphognathus and Soederberghia) occupy an apical position, and are separated from the earliest lungfishes by a paraphyletic assemblage of taxa generally identified as ‘chirodipterids’ and ‘dipterids.’ This finds broad agreement with the results of previous cladistic studies focused on non‐neurocranial data sets, but diverges from functional‐adaptive scenarios that posit three lineages of early lungfishes based on aspects of the dentition. As currently defined, both ‘chirodipterids’ and the genus Chirodipterus are heterogeneous assemblages; this analysis fails to find support for the monophyly of either. While this study indicates that Griphognathus is probably paraphyletic, it nevertheless supports a close relationship between the nominal species of this genus and Soederberghia. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 151 , 115–171.     

Birding and DNA: species for the new millennium

Capsule Based on the 1999 Witherby Memorial Lecture – reviews how developments in molecular and population genetics have led to a reappraisal of species limits in birds.

The taxonomy of birds of the West Palearctic has moved from the comparative stability of the ‘Voous List’ into a period of serious activity, with new data emerging in almost every issue of every evolutionary and avian journal! This activity comes from two directions. Firstly, developments in population genetics, molecular biology, acoustics, behaviour and distributional studies have opened new avenues to measuring differentiation among groups of birds. This, in turn, has led to the recognition that earlier views of what constitutes a ‘species’ are in need of modification (‘improvement’), and the emergence of the ‘lineage concept’ of species. I review some of the species concepts most relevant to avian studies, and attempt to show how and why this change has happened, and its consequences for taxonomy and species limits. Examples are given in the form of ‘case studies’, and include Carrion/Hooded Crows Corvus corone/cornix, Green-winged/Eurasian Teals Anas carolinensis/crecca and Phylloscopus warblers.     

Systematics,phylogeny and evolutionary pattern of the hystricognath rodent Eumysops (Echimyidae) from the Plio–Pleistocene of southern South America

?Eumysops is a peculiar representative of the currently tropical family Echimyidae, which evolved in increasingly dry and cold Plio–Pleistocene environments of southern South America. The results of a systematic and stratigraphic review of the genus, and of phylogenetic analyses based on both morphology and a combined morphological–molecular dataset in the context of extant representatives, are presented here. Recognised diversity includes four previously described species plus a new one from the late Pliocene. These species form a well-supported monophyletic clade, sister to the late Miocene ?Pampamys and the extant Thrichomys. The position of ?Eumysops–?Pampamys–Thrichomys in a major clade including non-‘eumysopine’ echimyids constrains the traditional taxon Eumysopinae only to these three genera. Phylogeny and stratigraphic distribution of ?Eumysops species suggest an essentially cladogenetic evolutionary pattern. Beyond this, a gradual directional change, involving increase in size and in molar hypsodonty, is shown by ?Eumysops chapalmalensis as part of a late Pliocene faunal turnover interpreted as a local representation of the 2.5-Ma cooling global event. Distinctive skeletal and dental anatomy of ?Eumysops, including large orbits, shortened braincase, marked hypsodonty and postcranial specialisations, would be a result of its southern history related to a particular palaeoclimatic context.     

Screening for resistance in apple cultivars to lightbrown apple moth, Epiphyas postvittana, and greenheaded leafroller, Planotortrix octo, and its relationship to field damage

The mature leaves of 38 apple (Malus domestica Borkh.) (Rosaceae) cultivars were screened for resistance to laboratory colonies of Epiphyas postvittana (Walker) and Planotortrix octo Dugdale (Lepidoptera: Tortricidae) by measuring larval survival and development rate, and pupal weight, in no‐choice laboratory bioassays in early summer. There were few cultivar effects on larval mortality but Nevis 1, A40R04T119, and ‘Sir Prize’ reduced survival of E. postvittana. Effects on development time and weight were correlated, and were integrated into a single measure of resistance R_c. R_c varied greatly between cultivars for both leafroller species, and identified 15 and 11 cultivars with partial resistance to E. postvittana and P. octo, respectively. A further experiment with three of the cultivars in midsummer, using the laboratory colonies in comparison with new colonies (from field collected larvae), produced similar results for E. postvittana, but there was no survival of new colony P. octo larvae on two cultivars. These results for P. octo are consistent with other recent research showing extreme cultivar resistance and critical colony and seasonal influences. A series of 4‐year field trials with the 38 cultivars showed poor correlation between laboratory and field resistance for the dominant leafroller species in the field, E. postvittana. The combined data, however, identified ‘Red Dougherty’, ‘Sir Prize’, and A40R04T119 as potentially useful in breeding for resistance to this species. The implications of these findings for integrated pest management (IPM) programmes and for the breeding of leafroller‐resistant apple cultivars are discussed.     

Taxonomic classification of the reef coral families Merulinidae,Montastraeidae, and Diploastraeidae (Cnidaria: Anthozoa: Scleractinia)

Modern coral taxonomy has begun to resolve many long‐standing problems in traditional systematics stemming from its reliance on skeletal macromorphology. By integrating examinations of colony, corallite, and subcorallite morphology with the molecular sequence data that have proliferated in the last decade, many taxa spread across the scleractinian tree of life have been incorporated into a rigorous classification underpinned by greater phylogenetic understanding. This monograph focuses on one of the most challenging clades recovered to date – its disarray epitomized by the informal name ‘Bigmessidae’. This group of predominantly Indo‐Pacific species previously comprised families Merulinidae, Faviidae, Pectiniidae, and Trachyphylliidae, but in a recent study these have been incorporated within Merulinidae. We studied 84 living merulinid species by examining morphological traits at three different scales of coral skeletal structure ? macromorphology, micromorphology, and microstructure ? to construct a morphological matrix comprising 44 characters. Data were analysed via maximum parsimony and also transformed onto a robust molecular phylogeny under the parsimony and maximum likelihood criteria. Comparisons amongst morphological character types suggest that although many characters at every scale are homoplastic, some to a greater extent than others, several can aid in distinguishing genus‐level clades. Our resulting trees and character analyses form the basis of a revised classification that spans a total of 139 species contained within 24 genera. The tree topologies necessitate the synonymization of Barabattoia as Dipsastraea, and Phymastrea as Favites. Furthermore, Astrea and Coelastrea are resurrected, and one new genus, P aramontastraea Huang & Budd gen. nov. , is described. All the genera in Merulinidae, along with the monotypic Montastraeidae and Diploastraeidae, are diagnosed based on the characters examined. The integrative classification system proposed here will form the framework for more accurate biodiversity estimates and guide the taxonomic placement of extinct species. © 2014 The Linnean Society of London     

Revision of the disparid Stylocrinus (Crinoidea) from the Devonian of Europe,Asia and Australia

Abstract: The discovery of new specimens and the restudy of known collections result in revision of the diagnosis and the stratigraphic distribution of the disparid crinoid genus Stylocrinus, from the Middle and Upper Devonian of Europe, Asia and Australia. The consistent development of three basal plates, the atomous arms with internally inclined edges adjoining laterally with adjacent brachials in an interlocking network and an apparently rudimentary pinnulation is recognised. The high ecophenotypic plasticity of the common species S. tabulatus negates the validity of several former subspecies and demonstrates the general morphologic variability of the aboral cup proportions. This contrasts with the low morphological spectrum of rarer stylocrinid species. With exclusion of ‘S. elimatus’ (Silurian) from Stylocrinus, the genus is limited to the Devonian. A neotype is proposed for the lost holotype of S. tabulatus. Stylocrinus prescheri sp. nov. is described from the Eifelian to Givetian of Europe and Asia. The first evidence of the gastropod grazing trace fossil Radulichnus on a crinoid aboral cup (S. tabulatus), the post‐mortem incurred ossicular‐boring of radial and basal plates as well as the post‐mortem encrusting by a rugose coral are further observations on Stylocrinus aboral cups.     

Molecular phylogeny and biogeography of African diploid barbs, ‘Barbus’, and allies in Africa and Asia (Teleostei: Cypriniformes)

African diploid barbs (‘Barbus’, Clypeobarbus, Barboides, etc.) are a group of small cyprinids with a body size less than 20 cm and widely distributed in drainages across Africa. These species constitute a significant component of African freshwater fish fauna. This study is the first to focus on the molecular systematics and biogeography of African diploid barbs ‘Barbus’ and its African and Asian allies using both mitochondrial and nuclear genes. We test for monophyly of groups, determine interspecific relationships and estimate the time of divergence of 52 species of ‘Barbus’ and allies using two mitochondrial and four nuclear genes. Resulting trees demonstrate that ‘Barbus’ and allies (Systomus, Barboides, Clypeobarbus and African tetraploid barbs) form a strongly supported clade; however, ‘Barbus’ is not resolved as monophyletic. Divergence time analyses identify the separation between Systomus and ‘Barbus’ plus African allies may have occurred around 26 MYA. In addition to the phylogenetic results, these findings highlight the need for more thorough taxonomic and systematic studies on ‘Barbus’ and allies using morphological and additional molecular data and greater taxon sampling, including the type species of the genus Enteromius, ‘Barbus’ potamogalis.     

Eunotia amazonica sp. nov. (Bacillariophyta), a common stalk-forming species from the Rio Negro basin (Brazilian Amazon)

A new stalk-forming diatom was observed at high relative abundances on periphytic samples collected in the Rio Negro hydrographic basin (Brazilian Amazon) and is here described using light and scanning electron microscopy. We also present ecological preferences of the new species. Eunotia amazonica sp. nov. co-dominated periphytic samples collected during the rainy seasons of 2013 and 2014 near the city of Manaus (Amazonas, Brazil). The main diagnostic feature of the new species is the stalk-forming growth form (‘Cymbella-like’) illustrated here for the first time in the genus Eunotia Ehrenberg. Previous reports on growth forms in common European databases for this genus included colonial (‘ribbon-like’) but also ‘mobile’, ‘fixed by pads’ or ‘without structures of fixation’. We demonstrated that the three dominant Eunotia species in periphytic samples from the Rio Negro all exhibited distinct ‘growth forms’ or habits: Eunotia amazonica sp. nov. (stalked), Eunotia intricans Metzeltin & Lange-Bertalot (ribbon-like) and Eunotia rabenhorstiana (Grunow) Hustedt (branched-arborescent). The high diversity of species, many of which are unknown to science, as well as the poorly known life-forms and habits of the Eunotiaceae in the region, partially prevent the use of metrics based on life-form to assess ecological changes. Generic assumptions based on robust statistical methods may obscure reality and lead to biased conclusions of diatom community changes in poorly explored regions such as Neotropical freshwater rivers, where the Eunotiaceae are largely dominant, particularly in the Amazon basin.