Emilio Insom

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.

Morphology, Morphogenesis, and Molecular Phylogeny of Paraparentocirrus sibillinensis n. gen., n. sp., a “Stylonychine Oxytrichidae” (Ciliophora, Hypotrichida) Without Transverse Cirri

A terrestrial oxytrichid ciliate Paraparentocirrus sibillinensis n. gen., n. sp., which was found in soil samples of a beech forest stand within the National Park of Sibillini Mountains, Italy, was investigated using live observation and protargol impregnation. The morphology of interphase, morphogenesis, and molecular phylogeny inferred from SSU rDNA sequences of this ciliate were studied. Paraparentocirrus n. gen., is mainly characterized by a semirigid body, an undulating membrane in the Oxytricha pattern, six fronto‐ventral (FV) rows, the absence of transverse cirri, one right and one left row of marginal cirri, four dorsal kineties, two dorsomarginal rows, and caudal cirri at the end of dorsal kinety 4. During morphogenesis, oral primordia develop through the proliferation of basal bodies from some cirri of FV rows 4 and 5, and FV row 6 takes part in the anlagen formation of the proter. The dorsal morphogenesis was typical of oxytrichids, with simple fragmentation of dorsal kinety 3, and the dorsomarginal rows developed from the right marginal row. Phylogenetic analyses based on the SSU rDNA sequences support the classification of this new genus in the stylonychines.

Advances, diversions, possible relapses and additional problems in understanding the early evolution of the Articulata

Abstract The authors review the available evidence concerning the early stages of radiation of the Articulata and support the hypothesis that there was probably a range of, perhaps incompletely, metameric organisms spanning, without definite borderlines, the early ancestors of arthropods, lobopods and annelids. By the early Cambrian, the stem lineages of the living articulate phyla were well‐identified, but there still survived a number of animals whose morphology spanned, to some extent, the gaps between the living taxa. The affinities between Annelida (sensu lato) and Mollusca are briefly discussed.

Cambrian Protochordata, their origin and significance

Abstract A survey of the available palaeontological and recent evidence points to the following interim conclusions: (a) animals belonging to the chordate lineage occurred in the Middle Cambrian, when they were already separated in at least three branches; (b) in the Middle Cambrian fossils the notochord may have been not or not entirely differentiated, nor did they have a perfect bilateral symmetry: myomeres, and most probably the nervous system being ≪off symmetry≫ by half a segment between the right and left half of the body, just as they presently are in the Acrania and, incompletely, in the Copelata and Cyclostomata; (c) in one of the Middle Cambrian taxa the skull was represented by skeletal material corresponding to the nonsegmental portions of that of living vertebrates and, as in living cyclostomes, probably derived entirely from neuroectodermal cells from the placodes and neural crest; (d) chordates may have evolved from Vendian animals showing the same type of incomplete bilateral symmetry; (e)...

Morphometric analysis of the kingfisher cranium (AVES)

This study demonstrates that both size and shape are important components of the morphological differentiation of the skull of subfamilies of kingfishers. Our findings are in partial agreement with those of previous taxonomic studies on kingfishers. Alcedinids and Halcyon spp. have a very similar braincase. The similarity among crania of the Cerylidae and Alcedinidae are largely related to the shape of the bill and the morphology of the musculature, which are in turn related to similarities in feeding habits. Halcyon amauroptera has a highly divergent bill and cranial shape compared to species of the genus Halcyon.