Alberto M. Simonetta

New animals from the Burgess Shale (Middle Cambrian) and their possible significance for the understanding of the Bilateria

Abstract The authors describe two new animals from the Middle‐Cambrian Burgess shale. One is formally described as Metaspriggina walcotti and is probably related to the sprigginids, and the other has probable Chordate affinities. Both share an imperfect bilateral symmetry, with alternating left and right segments, an arrangement found both in the Precambrian vendozoans and in the living Acrania and Cyclostomata. The authors discuss their possible evolutionary significance and the persistence of Precambrian‐like animals well into the Middle Cambrian.

Problems of systematics: Part 1. A critical evaluation of the ≪species problem≫ and its significance in evolutionary biology

Abstract The author discusses the significance of the ≪species problem≫ in the context of evolutionary biology and of systematics. He concludes that, contrary to current tendencies, a strongly nominalistic concept of the ≪species≫ is the only tenable one, that species cannot be conceived as individuals and that the species concept is irrelevant for evolutionary biology. Moreover a careful analysis of the species concept falsifies some of the basic tenets of Hennigian and of transformed cladism.

THE MORPHOLOGY OF THE SKULL IN NEOTENIC AND NORMAL TRITURUS VULGARIS MERIDIONALE (BOULENGER) (AMPHIBIA CAUDATA SALAMANDRIDAE)

SUMMARY The authors provide a detailed description of the skull in neotenic Triturus vulgaris meridionalis (Boulenger) (Amphibia Caudata Salamandridae) and compare it with the morphology of normal adults. The finds are also compared with published data concerning other urodeles. Though some interesting differences are found between the skull of normal and neotenic individuals, these do not plead in favour of the general hypothesis that neoteny has had a general role in the evolution of urodeles. The authors suggest that at an early stage of urodele evolution, telescoping of developmental phases occurred as an adaptation to short seasons favourable to larval development. The cranial kinesis of Triturus vulgaris is described in detail and this supports the contention by IORDANSKY (1982), contrary to current belief, that cranial kinesis is widespread among urodeles. Some features of cranial changes at metamorphosis appear to be linked with functional requirements.

Is Nectocaris pteryx a chordate

Abstract A revision of the morphology of Nectocaris pteryx Conway Morris, 1976, and a comparison with the morphology of living Chor‐dates supports the inclusion of Nectocaris in the phylum Chordata. The supposed somewhat crustacean‐like valves, which sheath the forepart of the animal are probably better considered as being the dermo‐epidermal folds that limit the peribranchial cavity of most lower Chordates, while the tail closely resembles the tail of the larval Tunicata and of Branchiostoma. The large eyes are a unique feature. A new subphylum within the Chordata is needed for Nectocaris.

Problems of systematics: Part 2. Theory and practice in phylogenetic studies and in systematics

Abstract In an attempt to further develop criticisms of Hennigian and of transformed cladism, I discuss how cladism can be refuted in all its basic principles, and why some important aspects of its methods should be discarded. Considering the present status of evolutionary zoology, some suggestions are made and amendments proposed to improve the International Rules for Zoological Nomenclature.

The phylogeny of the palaeozoic Arthropods

Abstract The Arthropoda form a natural phylum. The polyphyletic theories on the origin of Arthropods are rejected. The Palaeozoic Arthropods form a very complex assemblage and traditional taxonomic arrangement is inadequate to express their relationships.

Hypotheses on the origin and early evolution of chordates in the light of recent zoological and palaeontological evidence

Abstract Both new palaeontological and embryological evidence on chordates require a reassessment of traditional ideas on their early phylogeny and on the evolution of their Bauplan and tissues. A revision of the available data from both palaeontological and zoological points of view is useful both to clarify the better justified possible hypotheses and to point to the more profitable lines of investigation for further advancing our understanding of these problems. Recent advances in the knowledge of the morphology of Cambrian protochordates and of conodonts provide significant evidence for the understanding of the earliest phases of development of typical vertebrate morphology. It appears that, in the oldest lineages related with the evolution of vertebrates, mineralized tissues may have been restricted to the bucco‐pharyngeal region and be of ectodermal and ectomesenchymal origin. The development of dermal and visceral skeletal structures in living vertebrates further supports the overall significance o...

On the significance of ecotones in evolution and on the significance of morphologic differences in primitive taxa : reflections and hypotheses

Abstract The author discusses separately two problems of evolutionary biology: the probable significance of ecotones in favouring and directing evolution, and the biological significance of the, so called, higher taxa in the early phases of Metazoan evolution. For the second problem he argues that as is the Palaeozoic the niche system was ≪gross‐grained≫, major morphological differences, which by the current standards of neozoology should rank as of generic or even higher value, were merely of specific significance. Some taxinomic implications are discussed.

New fossil animals from the Middle Cambrian

Abstract A preliminary description is given of some specimens from Burgess Shale representing two unpublished species of metameric animals unassignable to any known phylum. The morphogenetic factors influencing the head shape of this sperm seem to be peculiar and probably related to the microtubular apparatus of the Sertoli cell.

Una possibile interpretazione filogenetica degli artropodi paleozoici

Abstract The Authors, after a brief discussion of the main evidence available, conclude that the Arthropods are presumably monophyletic and suggest a thentative phylogenetic arrangement of the palaeozoic Arthropods and of some peculiar mesozoic groups.