arXiv subjects

Michael Gudo

Publications and source records attributed to Michael Gudo.

3 recordsLinked to original sources

arXiv2008

100 Years of Deuterostomia (Grobben, 1908): Cladogenetic and Anagenetic Relations within the Notoneuralia Domain

Results from molecular systematics and comparative developmental genetics changed the picture of metazoan and especially bilaterian radiation. According to this new animal phylogeny (introduced by Adoutte et al. 1999/2000), Grobbens (1908) widely favoured protostome-deuterostome division of the Bilateria can be upheld, but only with major rearrangements within these superphyla. On the cladogenetic level, the Protostomia are split into two unexpected subgroups, the Lophotrochozoa and Ecdysozoa. The deuterostomes are split into the subgroups Chordata and Ambulacraria, which is not novel since Grobben (1908) introduced the Deuterostomia in this way (together with the Chaetognatha as a third line). However, many details of the new deuterostome phylogeny do not fit traditional, morphology-based reconstructions. As a consequence, three relatively unexpected proposals for early deuterostome evolution are favoured today: An ambulacraria-scenario, a xenoturbellid-scenario, and a chordate-scenario. The first two proposals are often discussed in the literature, while the chordate-scenario is almost completely neglected. Therefore, the paper presented focuses on the chordate scenario, i.e. the hypothesis of an acrania-like ur-deuterostomian. It is argued that the acrania-hypothesis is clearly preferable when biomechanic options of a polysegmented, hydroskeletal body plan are taken into account. The so called hydroskeleton hypothesis, rooted in the work of W. F. Gutmann, is the most detailed anagenetic scenario which depicts an acrania-like ur-deuterostome.

q-bio.PE↗

arXiv2005

Hydromechanical considerations on the evolution and diversification of the echinoderm bauplans

The pentaradial organisation of echinoderms is postulated to have evolved as the result of the reorganisation of the internal U-shaped mesentery of the intestinal tract during inflation of the trunk of a pterobranch-like ancestor. Under this scenario, loops of the mesentery developed between five hydraulic bulges by three different mechanisms: (1) by the early formation of two additional loops resulting directly in five hydraulic bulges, (2) by the subsequent formation of two additional loops resulting in the formation of initially three and then five hydraulic bulges or (3) by the inflation of the body without formation of loops. Accordingly there are at least three main evolutionary pathways within the echinoderms. The anatomical structures, such as the ambulacral system or the skeletal capsule, which characterize the echinoderms, developed independently in both lineages. From all the three pathways various body structures can be derived matching those found in fossil and extant echinoderms. The eleutherozoans and the earliest pentaradial echinoderms most likely evolved from the direct-pentaradial pathway whereas triradiate echinoderms and those which show a pentaradial organisation superimposed on triradial symmetry, likely evolved along the indirect pathway. The asymmetric or bilateral symmetric echinoderms evolved from the third paythway. The most important morphological transformations leading to the directly and indirectly pentaradial echinoderms are discussed and described.

q-bio.PE↗

arXiv2005

Hydromechanical considerations on the origin of the pentaradial body structure of echinoderms

When echinoderms are conceptualized as hydraulic entities, the early evolution of this group can be presented in a scenario which describes how a bilateral ancestor (an enteropneust-like organism) gradually evolved into a pentaradial echinoderm. According to this scenario, the arms are outgrowths from the anterior/posterior body axis of the bilateral pterobranchia-like intermediate. These outgrowths developed when the originally U-shaped mesentery of the intestinal tract formed loops, and correspondingly, the tensile chords of the mesentery were attached to the body wall in five loops. The wall faces between these regions of tensile chords could bulge out under the hydraulic pressure of the body coelom. The originally more or less round body cavity was deformed into a pneu with five bulges. The loops of the gut forced a roughly symmetric arrangement, which was enhanced by a physical fact: five pneus as well as one pneu with five internal tethers, naturally adopt a pentaradial pattern of "minimum contact surfaces", as the most economic arrangement. These evolutionary transformations were accompanied by certain histological modifications, such as the development of mutable connective tissues and skeletal elements that fused to ossicles and provided shape stabilization in the form of a calcareous skeleton in the tissues of the body wall. The resultant organism was an ancestral eleutherozoan echinoderm (Ur-Echinoderm).

q-bio.PE↗