Single Phylum Research Articles

Phylum-specific environmental DNA analysis reveals remarkably high global biodiversity of Cercozoa (Protozoa)

This study presents the first 18S rRNA multi-library environmental PCR survey of a single protozoan phylum, Cercozoa Cavalier-Smith 1998, from a range of different habitats. Phylogenetic analysis reveals at least nine novel clades within the phylum, several possibly at the level of order or above. Further experiments are described to ascertain the true ecological and geographical distributions of some clades that might be inferred from the tree to be restricted in either or both ways. These results suggest that the diversity of cercozoan taxa may run into thousands of lineages, making it comparable in diversity to the largest better-characterized protozoan phyla, e.g. Ciliophora (ciliates and suctorians) and Foraminifera. New sequences of cultured Spongomonas, Metromonas and Metopion are also presented. In the light of these additions, and the increased taxon sampling from the environmental libraries, some revisions of cercozoan classification are made: the transfer of Spongomonadea from Reticulofilosa to Monadofilosa; the removal of Metopiida from Sarcomonadea; and the creation of the new order Metromonadida, currently containing the single genus Metromonas. Although Metromonas groups with weak to moderate support with Chlorarachnea, it is here placed in superclass Monadofilosa, to which it is morphologically more similar.

Genome evolution in yeasts.

Identifying the mechanisms of eukaryotic genome evolution by comparative genomics is often complicated by the multiplicity of events that have taken place throughout the history of individual lineages, leaving only distorted and superimposed traces in the genome of each living organism. The hemiascomycete yeasts, with their compact genomes, similar lifestyle and distinct sexual and physiological properties, provide a unique opportunity to explore such mechanisms. We present here the complete, assembled genome sequences of four yeast species, selected to represent a broad evolutionary range within a single eukaryotic phylum, that after analysis proved to be molecularly as diverse as the entire phylum of chordates. A total of approximately 24,200 novel genes were identified, the translation products of which were classified together with Saccharomyces cerevisiae proteins into about 4,700 families, forming the basis for interspecific comparisons. Analysis of chromosome maps and genome redundancies reveal that the different yeast lineages have evolved through a marked interplay between several distinct molecular mechanisms, including tandem gene repeat formation, segmental duplication, a massive genome duplication and extensive gene loss.

The Phylogeny and Signature Sequences Characteristics of Fibrobacteres, Chlorobi, and Bacteroidetes

Fibrobacteres, Chlorobi, and Bacteroidetes (FCB group) comprise three main bacterial phyla recognized on the basis of 16S rRNA trees. Presently, there are no distinctive biochemical or molecular characteristics known that can distinguish these bacteria from other bacterial phyla. The relationship of these bacteria to other phyla is also not known. This review describes many signatures, consisting of defined and conserved inserts in widely distributed proteins, that provide distinctive molecular markers for these groups of bacteria. These signatures serve to clarify the evolutionary relationship between members of the FCB group, and to other bacterial phyla. A 4 aa insert in DNA Gyrase B (GyrB) and a 45 aa insert in the SecA proteins are uniquely shared by various Bacteroidetes species. The insert in GyrB is present in all Bacteroidetes species (>100) covering different orders and families, indicating that it is a distinctive characteristic of the group. Three signatures consisting of an 18 aa insert in ATPase α-subunit, an 8–9 aa insert in the FtsK protein and a 1 aa insert in the UvrB protein are commonly shared only by the Bacteroidetes and Chlorobi homologs providing evidence that these two groups are specifically related to each other. Two additional inserts in the RNA polymerase β′-subunit (5–7 aa) and Serine hydroxymethyl-transferase (14–16 aa), which are commonly present in various Bacteroidetes, Chlorobi, and Fibrobacteres homologs, but not any other bacteria, provide evidence that these groups shared a common ancestor exclusive of all other bacteria. The FCB groups of bacteria are indicated to have diverged from this common ancestor in the following order: Fibrobacteres → Chlorobi → Bacteriodetes. The inferences from signature sequences are strongly supported by phylogenetic analyses. These observations suggest that the FCB groups of bacteria should be placed in a single phylum rather than three distinct phyla. Signature sequences in a number of other proteins provide evidence that the FCB group of bacteria diverged at a similar time as the Chlamydiae group, and that the Spirochetes and Aquificales groups are its closest relatives.

Molecular and culture-based analyses of prokaryotic communities from an agricultural soil and the burrows and casts of the earthworm Lumbricus rubellus.

The microbial populations in no-till agricultural soil and casts of the earthworm Lumbricus rubellus were examined by culturing and molecular methods. Clone libraries of the 16S rRNA genes were prepared from DNA isolated directly from the soil and earthworm casts. Although no single phylum dominated the soil library of 95 clones, the largest numbers of clones were from Acidobacteria (14%), Cytophagales (13%), Chloroflexi (8%), and gamma-Proteobacteria (8%). While the cast clone library of 102 clones was similar to the soil library, the abundances of several taxa were different. Representatives of the Pseudomonas genus as well as the Actinobacteria and Firmicutes increased in number, and one group of unclassified organisms found in the soil library was absent in the cast library. Likewise, soil and cast archaeal 16S rRNA gene libraries were similar, although the abundances of some groups were different. Two hundred and thirty aerobic bacteria were also isolated on general heterotrophic media from casts, burrows, and soil. The cast isolates were both phenotypically and genotypically different from the soil isolates. The cast isolates were more likely to reduce nitrate, grow on acetate and Casamino Acids, and utilize fewer sugars than the soil isolates. On the basis of their ribotypes, the cast isolates were dominated by Aeromonas spp. (28%), which were not found in the soil isolates, and other gamma-Proteobacteria (49%). In contrast, the soil isolates were mostly Actinobacteria (53%), Firmicutes (16%), and gamma-Proteobacteria (19%). Isolates obtained from the sides of earthworm burrows were not different from the soil isolates. Diversity indices for the collections of isolates as well as rRNA gene libraries indicated that the species richness and evenness were decreased in the casts from their levels in the soil. These results were consistent with a model where a large portion of the microbial population in soil passes through the gastrointestinal tract of the earthworm unchanged while representatives of some phyla increase in abundance.

The overwhelming variety of life

The overwhelming variety of life

Ecological communities: conceptual problems and definitions

Three major problems with respect to ecological communities are tackled. The first is the problem of ambiguity, i.e. the fact that the term “community” is being used for various kinds of objects at different levels of organisation. We argue that this problem can be resolved by restricting use of the term “community” to sets of co-occurring organisms belonging to a single taxonomic phylum or class (plants, birds, insects, etc.) and by using the term “biocoenosis” for sets of organisms belonging to multiple phyla or classes and comprising the biotic components of ecosystems. We also argue that interaction between organisms is neither a necessary nor a sufficient condition for community membership, or, in other words, that communities may consist of both interacting and non-interacting organisms. The second and third problems are the boundary problem and the problem of heterogeneity, i.e. the fact that communities, as currently defined, most often do not have discrete boundaries and are quite heterogeneous with respect to species composition. We argue that both problems result from the fact that communities are seen as groups of co-occurring populations of species, whereas actually populations of different species rarely if ever co-occur in exactly the same area. These problems can be resolved by redefining communities as particular sets of individuals occurring in the intersection of the areas occupied by different populations of species. In the final section we defend our definition against some potential objections, viz. (1) that it would lead to an excessive number of small communities, especially in species-rich situations, and (2) that, because population boundaries may change all the time, such communities would be very unstable.

A Cladistic Analysis of Pseudocoelomate (Aschelminth) Morphology

We investigated possible relationships among pseudocoelomates (aschelminths) by using cladistic analysis to uncover all most-parsimonious trees from a data set comprising 45 morphological characters of 11 phyla (3 acoelomate, 7 pseudocoelomate, and 1 coelomate). Analysis of our matrix yielded 2 most-parsimonious trees, differing only in relative placement of 3 taxa (Kinorhyncha, Loricifera, and Priapulida). Tree topology suggests that the pseudocoel either evolved twice, or that it evolved once and was then independently lost in Gastrotricha and in Gnathostomulida. Tree topology also is consistent with derivation of the pseudocoel from a coelom. From our analysis and that of other morphologically-based studies, we conclude that there are 2 main lines of pseudocoelomate evolution: (1) a minor clade (Acanthocephala + Rotifera) defined principally by a syncytial epidermis, intracytoplasmic lamina, and sperms with anterior flagella; (2) a major clade (the 5 remaining phyla), defined primarily by a cuticle that is molted. Within the major clade are 2 subclades (Nematoda + Nematomorpha; Kinorhyncha + Loricifera + Priapulida). Using morphological data, the chief issues remaining to be resolved are placement of Gastrotricha and Gnathostomulida, and evolution of the pseudocoel. No analysis based solely on morphological data has so far produced a tree congruent with those based on molecular data. Nevertheless, there is a general consensus that (1) the pseudocoel is of little phylogenetic significance and (2) the pseudocoelomates are probably polyphyletic. Additional key words: evolution, phylogeny the face of this bewildering array of conflicting opinions about the interrelationships of the aschelminth phyla, it is impossible to form a coherent picture of the evolution of the animals. (Clark 1964) Does Clark's observation made some 30 years ago still offer a realistic view of our understanding of pseudocoelomate (aschelminth) phylogeny? Clearly, these vermiform taxa share interesting similarities. However, they also possess some striking differences, which have led many authors to choose not to include them in a single phylum, the Aschelminthes (e.g., Clark 1964; Anderson 1983; Inglis 1985; Pearse et al. 1987; Brusca & Brusca 1990; Kozloff 1990; Willmer 1990; Ruppert & Barnes 1994). In fact, for Inglis (1985) there is no common history at all, just completely independent solutions to similar evolutionary pressures. Further complicating the matter is Ruppert's (1991) view that calls into question the significance of 2 traditional characters that link the pseudocoelomates: pseudocoel and cuticle (see also Brusca & Brusca 1990). The alternative position, of course, argues for at least a loose relationship among some of these taxa (e.g., Hyman 1951; Boaden 1985; Lorenzen 1985; Sterrer et al. 1985; Bergstrom 1991; Meglitsch & Schram 1991; Malakhov 1994). The problem is to dissect possible relationships from what appears to be an intractable array of characteristics. However, there is no reason to abandon the logical search for phylogenetic relationships among these taxa. In fact, many workers have explored this field, with phylogenetic analyses that include most or all of the appropriate taxa (e.g., Lorenzen 1985; Meglitsch & Schram 1991; Schram 1991; Eernisse et al. 1992; Conway Morris 1994; Nielsen 1994; 1995; Neuhaus 1994; Winnepenninckx et al. 1995). Here we report our findings from a cladistic analysis of 45 morphological characters and 11 taxa (3 acoelomate, 7 pseudocoelomate, and 1 coelomate). We also compared trees yielded from this study to other published works. Thus, the purposes of this study were to assemble a useful set of light microscopical, ultrastructural, and biochemical characters on the pseudocoelomate taxa and to develop parsimonious cladograms (hypotheses) from those data. Such work may provide a useful foundation for the molecular data that are now forthcoming (e.g., Lake 1990; Brandl et al. 1992; This content downloaded from 157.55.39.30 on Wed, 20 Jul 2016 06:18:46 UTC All use subject to http://about.jstor.org/terms Phylogeny of pseudocoelomates Smothers et al. 1994; Garey et al. 1995; Winnepenninckx et al. 1995). A combination of morphological and molecular data may eventually lead to a comprehensive phylogeny of these taxa (cf. Hillis 1987; Patterson et al. 1993).

Some physical problems in biology

A review is presented within the framework of the theory of evolution, after it has been extrapolated from the population level to the cellular and molecular levels. From Darwin's seminal and persuasive insight - the theory of common descent - we assume, with him, that “probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed” [1]. We are now aware that this primordial cell may have been a protocyanobacterium, but it has often been called ‘a last universal ancestor’, a ‘breakthrough organism’, or a ‘progenote’, a term introduced by Woese [2] which has gained wide acceptance. Strictly speaking, in the ‘intermediate period’, ranging from the first living cell to the progenote, life may have evolved in the absence of significant diversity, effectively as a single phylum, incorporating organisms whose genetic systems were already based on DNA. Earlier still, prior to the encapsulation of nucleic acids in microspheres, evolution may already have been at work on RNA molecules (the ‘RNA world’). This takes our discussion into the period of chemical evolution, a concept first put forward by Oparin [3], whose principal merit is to have formulated the underlying problem in clear scientific terms. This review does not attempt to be comprehensive. It is mainly devoted to the discussion of certain concepts that may have played a relevant role in the pathway that led to the origin and evolution of the progenote. We do not dwell on the main events of the intermediate period. The topics that we have chosen to include are: the origin of chirality of protein amino acids, the origin of translation, and the origin of the genome. We conclude with some comments on one further aspect of the evolutionary process - the development of biodiversity - by considering the origin of the first eukaryotic cell, an event which, according to the fossil record, may have preceded the evolutionary radiation in the early Cambrian by over a billion years.

Kingdom protozoa and its 18 phyla.

The demarcation of protist kingdoms is reviewed, a complete revised classification down to the level of subclass is provided for the kingdoms Protozoa, Archezoa, and Chromista, and the phylogenetic basis of the revised classification is outlined. Removal of Archezoa because of their ancestral absence of mitochondria, peroxisomes, and Golgi dictyosomes makes the kingdom Protozoa much more homogeneous: they all either have mitochondria and peroxisomes or have secondarily lost them. Predominantly phagotrophic, Protozoa are distinguished from the mainly photosynthetic kingdom Chromista (Chlorarachniophyta, Cryptista, Heterokonta, and Haptophyta) by the absence of epiciliary retronemes (rigid thrust-reversing tubular ciliary hairs) and by the lack of two additional membranes outside their chloroplast envelopes. The kingdom Protozoa has two subkingdoms: Adictyozoa, without Golgi dictyosomes, containing only the phylum Percolozoa (flagellates and amoeboflagellates); and Dictyozoa, made up of 17 phyla with Golgi dictyosomes. Dictyozoa are divided into two branches: (i) Parabasalia, a single phylum with hydrogenosomes and 70S ribosomes but no mitochondria, Golgi dictyosomes associated with striated roots, and a kinetid of four or five cilia; and (ii) Bikonta (16 unicellular or plasmodial phyla with mitochondria and bikinetids and in which Golgi dictyosomes are not associated with striated ciliary roots), which are divided into two infrakingdoms: Euglenozoa (flagellates with discoid mitochondrial cristae and trans-splicing of miniexons for all nuclear genes) and Neozoa (15 phyla of more advanced protozoa with tubular or flat [usually nondiscoid] mitochondrial cristae and cis-spliced spliceosomal introns). Neozoa are divided into seven parvkingdoms: (i) Ciliomyxa (three predominantly ciliated phyla with tubular mitochondrial cristae but no cortical alveoli, i.e., Opalozoa [flagellates with tubular cristae], Mycetozoa [slime molds], and Choanozoa [choanoflagellates, with flattened cristae]); (ii) Alveolata (three phyla with cortical alveoli and tubular mitochondrial cristae, i.e., Dinozoa [Dinoflagellata and Protalveolata], Apicomplexa, and Ciliophora); (iii) Neosarcodina (phyla Rhizopoda [lobose and filose amoebae] and Reticulosa [foraminifera; reticulopodial amoebae], usually with tubular cristae); (iv) Actinopoda (two phyla with axopodia: Heliozoa and Radiozoa [Radiolaria, Acantharia]); (v) Entamoebia (a single phylum of amoebae with no mitochondria, peroxisomes, hydrogenosomes, or cilia and with transient intranuclear centrosomes); (vi) Myxozoa (three endoparasitic phyla with multicellular spores, mitochondria, and no cilia: Myxosporidia, Haplosporidia, and Paramyxia); and (vii) Mesozoa (multicells with tubular mitochondrial cristae, included in Protozoa because, unlike animals, they lack collagenous connective tissue).

Kingdom protozoa and its 18 phyla.

The demarcation of protist kingdoms is reviewed, a complete revised classification down to the level of subclass is provided for the kingdoms Protozoa, Archezoa, and Chromista, and the phylogenetic basis of the revised classification is outlined. Removal of Archezoa because of their ancestral absence of mitochondria, peroxisomes, and Golgi dictyosomes makes the kingdom Protozoa much more homogeneous: they all either have mitochondria and peroxisomes or have secondarily lost them. Predominantly phagotrophic, Protozoa are distinguished from the mainly photosynthetic kingdom Chromista (Chlorarachniophyta, Cryptista, Heterokonta, and Haptophyta) by the absence of epiciliary retronemes (rigid thrust-reversing tubular ciliary hairs) and by the lack of two additional membranes outside their chloroplast envelopes. The kingdom Protozoa has two subkingdoms: Adictyozoa, without Golgi dictyosomes, containing only the phylum Percolozoa (flagellates and amoeboflagellates); and Dictyozoa, made up of 17 phyla with Golgi dictyosomes. Dictyozoa are divided into two branches: (i) Parabasalia, a single phylum with hydrogenosomes and 70S ribosomes but no mitochondria, Golgi dictyosomes associated with striated roots, and a kinetid of four or five cilia; and (ii) Bikonta (16 unicellular or plasmodial phyla with mitochondria and bikinetids and in which Golgi dictyosomes are not associated with striated ciliary roots), which are divided into two infrakingdoms: Euglenozoa (flagellates with discoid mitochondrial cristae and trans-splicing of miniexons for all nuclear genes) and Neozoa (15 phyla of more advanced protozoa with tubular or flat [usually nondiscoid] mitochondrial cristae and cis-spliced spliceosomal introns). Neozoa are divided into seven parvkingdoms: (i) Ciliomyxa (three predominantly ciliated phyla with tubular mitochondrial cristae but no cortical alveoli, i.e., Opalozoa [flagellates with tubular cristae], Mycetozoa [slime molds], and Choanozoa [choanoflagellates, with flattened cristae]); (ii) Alveolata (three phyla with cortical alveoli and tubular mitochondrial cristae, i.e., Dinozoa [Dinoflagellata and Protalveolata], Apicomplexa, and Ciliophora); (iii) Neosarcodina (phyla Rhizopoda [lobose and filose amoebae] and Reticulosa [foraminifera; reticulopodial amoebae], usually with tubular cristae); (iv) Actinopoda (two phyla with axopodia: Heliozoa and Radiozoa [Radiolaria, Acantharia]); (v) Entamoebia (a single phylum of amoebae with no mitochondria, peroxisomes, hydrogenosomes, or cilia and with transient intranuclear centrosomes); (vi) Myxozoa (three endoparasitic phyla with multicellular spores, mitochondria, and no cilia: Myxosporidia, Haplosporidia, and Paramyxia); and (vii) Mesozoa (multicells with tubular mitochondrial cristae, included in Protozoa because, unlike animals, they lack collagenous connective tissue).

Segmentation and Segmental Differentiation in the Development of the Central Nervous Systems of Leeches and Flies

There are two current views regarding the phyletic organization of the arthropods. In one view, all arthropods [chelicerates, crustaceans, and uniramians (onychophorans, myriapods, and hexapods)] belong to a single phylum, arising through a complex evolutionary radiation that occurred some 500 to 600 million years ago; the second view holds that the arthro­ pods are polyphyletic, since embryological features suggest separate evo­ lutionary relationships between polychaetes and crustaceans, and between oligochaetes and uniramians (Anderson 1 973, Gupta 1979). Regardless which of these is correct, the metamerism of annelids and arthropods is generally thought to have arisen in a common ancestor of both groups, and both structural and embryological analyses provide evidence for a close relationship between the two groups. One such analysis of several shared features has led to the proposal of a particular phylogenetic affinity between leeches and insects (Sawyer 1 984). The relative closeness of these relationships has been somewhat compromised, however, by recent cross­ species comparisons of nucleic acid sequences. Metamery is also a feature of the chordates, and, interestingly, sequence analysis of 18s rRNA does not indicate that, among the eucoelomates, annelids and arthropods are

ChemInform Abstract: THE VARIED AND FASCINATING CHEMISTRY OF MARINE MOLLUSKS

With illustrations from a single phylum of marine invertebrates, the mollusks, this review presents a cross section of recent marine natural product research. The origins of this research, biological, biomedical, chemical, or serendipitous, are presented as well as the results.

The Varied and Fascinating Chemistry of Marine Mollusks

AbstractWith illustrations from a single phylum of marine invertebrates, the mollusks, this review presents a cross section of recent marine natural product research. The origins of this research, biological, biomedical, chemical, or serendipitous, are presented as well as the results.

A Simple Model Illustrating Problems of Phylogeny and Classification

A model consisting of 37 pieces of hardware, representing as many animal species in a single phylum, has been used successfully at several levels of undergraduate and postgraduate experience to teach problems of beta taxonomy and the arbitrariness, subjectivity, and limitations of higher classifications. Students find this model challenging, stimulating, and thoroughly engaging. The model is simple, durable, inexpensive, and easy to manipulate; it fits comfortably in one laboratory period; it involves a minimum of characters; and it presupposes no familiarity with the morphology and accompanying jargon of any particular group of organisms. Although my chief systematic interests lie at and around the species level, this paper reports a laboratory exercise concocted in January 1963 to illuminate major problems commonly encountered in the synthetic taxonomic process of delimiting higher categories. Students are often at best but dimly aware of problems at this level and, in particular, of the arbitrariness, subjectivity, and limitations of higher classifications. Classifications themselves are undeniably useful; unfortunately their utilization on the part of many students is virtually blind. I designed the following exercise for a single laboratory period of the introductory biology course at Wesleyan University, primarily to provide critical insight into various aspects of beta taxonomy but, secondarily, to offer some relief and mindexpansion in a largely cellular-molecular undergraduate curriculum. The exercise has been well received in five years of use in introductory biology. Moreover, it has provoked interest and enthusiasm at other levels of biological sophistication: from undergraduates in science courses for non-science majors at Wesleyan; from graduate students in a course in speciation at Mountain Lake Biological Station of the University of Virginia; and from college and university teachers in a summer institute for teachers of biology at Williams College. I usually preface the exercise with an exploratory lecture or discussion of relevant features of taxonomic theory and append a moderate reading assignment to assure an adequate background. Despite a few differences of opinion on specific points, I still favor the terse account of taxonomic principles on pages 1 to 24 in Simpson (Bull. Amer. Mus. Nat. Hist., 85, 1945: 1-350). The exercise is in two parts, of which the first is by far the more important.

Evolution of Zooparasitic Groups in the Phylum Nematoda, with Special Reference to Host-Distribution

In the NEMATODA the biologist is confronted with a well-defined group of organisms, relatively small as regards different structural types, but exceedingly numerous as individuals and successful in the most varied habitats. Traditionally in general zoology and parasitology texts-in the English language, at least-the group is considered an order or class, which, with orders or classes GORDIACEA (or NEMATOMORPHA) and ACANTHOCEPHALA, constitutes a phylum NEMATHELMINTHES. However, as the leading nematologist, B. G. Chitwood (1950c), has pointed out in a review of the historical placement of the NEMATODA in the animal kingdom, such a grouping has never had the support of serious students of invertebrate evolution. H-e has marshaled evidence in a succinct manner for the view, recognized by a growing number of zoologists, that the nematodes constitute the largest of a group of minor phyla--or classes within a rather broadly defined phylum, to which Hyman (1940, 1951a, b [in press]) has followed earlier German workers in applying the name ASCHELMINTHES Grobben, 1908. Whether one wishes to consider the NEMATODA an independent phylum or an aschelminth class is of relatively minor importance (although it may be remarked that there is probably more justification in combining the ANNELIDA, ONYCHOPHORA, and ARTHROPODA into a single phylum than the so-called aschelminth classes). For present purposes I am considering the NEMATODA a phylum. What is actually important is recognition of the interesting evolutionary status of the NEMATODA. They represent one of a group of Nature's minor evolutionary experiments in metazoan organization and have exploited various possibilities of non-segmented, pseudocoelomatous, vermiform structure. They have never attained the remarkable diversity of the major animal phyla-in particular the MOLLUSCA, ARTHROPODA, and CHORDATA-presumably because evolutionary processes have been able to do only so

Expanding Horizons in the Recognition of a Phylum

The field of systematics has often been ridiculed, especially by biologists engaged in other aspects of science. Occasionally the writings of some systematists have merited this lack of respect but this fact provides neither reason nor excuse for belittling the entire field. The chief cause for contempt of systematics has been a lack of appreciation on the part of other biologists for the methods and objectives of taxonomic work. There has been a wide spread but fallacious belief that physical and chemical phenomena are objective realities while species and other taxonomic concepts are purely subjective creations of the human imagination. The apparent disregard for taxonomy has some times been voiced in the figure which rates the taxonomists as the hod-carriers of science. Those who hold such derogatory attitude toward the objectives of the taxonomist seem to have forgotten that the mortar carried by the hod-carrier is the stuff which gives stability to the wall. Without cooperation of hod carriers, the walls of biology would be but a loose pile of toppling bricks or stones, lacking pattern and orderliness. However, if the taxonomist is rated as but a menial laborer whose function is that of carrying the cohesive mortar for the edifice of biology, how much lower in the social scale of scientific castes must be the student of nomenclature who inspects the bricks for conformity and rejects those with flaws before they weaken the wall. All too often faulty material escapes first inspection and then part of the structure must be torn down so that the defective units may be replaced. To carry the figure a bit farther; we might say that the student of nomenclature is the apprentice to the hod-carrier since it is he who moistens the sand of personal endeavor and the lime of public opinion with the water of common sense and precedent to form the mortar for binding together the units constituting the structure of taxonomy. Instead of attempting to organize a brief in defense of the fields and practices of taxonomy and nomenclature, this address will be devoted to tracing the growth of information regarding a single phylum, the Acanthocephala, or thorny-headed worms. In its history this group provides excellent material to illustrate the steps in the gradual expansion and evaluation of concepts in taxonomy. In the earliest days before the status of this group was understood, species now regarded as belonging within it were promiscuously assigned to various genera now recognized as representing several distinct phyla. By easy stages the knowledge of detailed

Wisconsin Silurian Bioherms (Organic Reefs)

The Silurian of Wisconsin contains biohermal structures at several stratigraphic horizons. These bioherms are essentially cuboidal, domal, or ridgelike masses of porous and cavernous, crudely bedded and poorly jointed, barren to highly fossiliferous dolomites which grade peripherally outward and vertically upward and downward into well-bedded, dense to saccharoidal, relatively unfossiliferous dolomites. The approximately contemporaneous surrounding strata, which commonly are thin bedded, first dip away from the reefy mounds at relatively low angles, except where differential slumping has steepened the initial dip, and then become essentially horizontal and take on the lithological character of the normal stratigraphic sequence of the region. The complexity of the fauna on some of the bioherms shows clearly that no single phylum of organisms played the dominant role in the construction. On the contrary, it is usually obvious that many different classes of organisms made large and important contributions to the growing calcareous mounds. Chief among the bioherm builders were algae, hydrozooid stromatoporoids, tabulate corals, camerate crinoids, cryptostomatous bryozoans, protrematous and telotrematous brachiopods, pelecypods, gastropods and cephalopods, and trilobites. Biohermal sites, especially at Wauwatosa, Milwaukee, and in the vicinity of Cedarburg and Grafton, were the main sources of the several large Silurian collections made by local amateur collectors in the closing decades of the nineteenth century; they still remain among the best collecting sites. The interbiohermal strata may or may not be fossiliferous, but if they are their fauna tends to be small and somewhat different from the typical biohermal assemblage. The bioherms appear to have accumulated in fairly shallow water and to have stood as low mounds a few feet to a few tens of feet above the surrounding bottoms where fine calcareous muds were being deposited.

Systematic Position of the Slime Molds and Its Bearing on the Classification of the Fungi

1. The Myxomycetes have been regarded both as fungi and as animals. If the fungi are thought of as descended from green algae either as a monophyletic or polyphyletic group, the Myxomycetes are excluded. If, however, the fungi are regarded as a monophyletic group descended from colorless flagellates, the Myxomycetes form a natural class, the lowest of four, the others being the Phycomycetes, the Ascomycetes, and the Basidiomycetes. It is suggested that the fungi be regarded as a phylum which has not definitely developed into either plants or animals, but may be grouped with the former as a matter of convenience, and in accordance with custom. It is pointed out that the familiar assumption that all living organisms are descended from a single primitive cell is unwarranted and less in accord with what we know concerning living organisms than the assumption that life may have originated more than once and in different forms. 2. It is suggested that the words fungus, assimilative and saprobe, and appropriate derivatives, be used instead of plant, vegetative, and saprophyte, in referring to fungi. 3. The differences between the Myxomycetes and the Phycomycetes which are usually held to indicate a sharp separation of the two groups are considered, and it is maintained that these differences are neither so absolute nor so fundamental as is ordinarily believed, and may be recognized adequately by regarding them as distinct classes of a single phylum.