scholarly journals Origins of radial symmetry identified in an echinoderm during adult development and the inferred axes of ancestral bilateral symmetry

2007 ◽  
Vol 274 (1617) ◽  
pp. 1511-1516 ◽  
Author(s):  
Valerie B Morris
Keyword(s):  
Sea Urchin ◽  
Adult Development ◽  
Bilateral Symmetry ◽  
Radial Symmetry ◽  
Body Plan ◽  
Direct Development ◽  
The Common ◽  
Patterning Genes ◽  
Standing Problem

How the radial body plan of echinoderms is related to the bilateral body plan of their deuterostome relatives, the hemichordates and the chordates, has been a long-standing problem. Now, using direct development in a sea urchin, I show that the first radially arranged structures, the five primary podia, form from a dorsal and a ventral hydrocoele at the oral end of the archenteron. There is a bilateral plane of symmetry through the podia, the mouth, the archenteron and the blastopore. This adult bilateral plane is thus homologous with the bilateral plane of bilateral metazoans and a relationship between the radial and bilateral body plans is identified. I conclude that echinoderms retain and use the bilateral patterning genes of the common deuterostome ancestor. Homologies with the early echinoderms of the Cambrian era and between the dorsal hydrocoele, the chordate notochord and the proboscis coelom of hemichordates become evident.

scholarly journals The early Cambrian fossil embryo Pseudooides is a direct-developing cnidarian, not an early ecdysozoan

2017 ◽  
Vol 284 (1869) ◽  
pp. 20172188 ◽  
Author(s):  
Baichuan Duan ◽  
Xi-Ping Dong ◽  
Luis Porras ◽  
Kelly Vargas ◽  
John A. Cunningham ◽  
...  
Keyword(s):  
Phylogenetic Analysis ◽  
Developmental Stages ◽  
Radial Symmetry ◽  
Body Plan ◽  
Direct Development ◽  
Early Cambrian ◽  
Germ Band ◽  
Stages Of Development ◽  
Bayesian Phylogenetic Analysis ◽  
Indirect Development

Early Cambrian Pseudooides prima has been described from embryonic and post-embryonic stages of development, exhibiting long germ-band development. There has been some debate about the pattern of segmentation, but this interpretation, as among the earliest records of ecdysozoans, has been generally accepted. Here, we show that the ‘germ band’ of P. prima embryos separates along its mid axis during development, with the transverse furrows between the ‘somites’ unfolding into the polar aperture of the ten-sided theca of Hexaconularia sichuanensis , conventionally interpreted as a scyphozoan cnidarian; co-occurring post-embryonic remains of ecdysozoans are unrelated. We recognize H. sichuanensis as a junior synonym of P. prima as a consequence of identifying these two form-taxa as distinct developmental stages of the same organism. Direct development in P. prima parallels the co-occuring olivooids Olivooides, and Quadrapyrgites and Bayesian phylogenetic analysis of a novel phenotype dataset indicates that, despite differences in their tetra-, penta- and pseudo-hexa-radial symmetry, these hexangulaconulariids comprise a clade of scyphozoan medusozoans, with Arthrochites and conulariids, that all exhibit direct development from embryo to thecate polyp. The affinity of hexangulaconulariids and olivooids to extant scyphozoan medusozoans indicates that the prevalence of tetraradial symmetry and indirect development are a vestige of a broader spectrum of body-plan symmetries and developmental modes that was manifest in their early Phanerozoic counterparts.

scholarly journals Trends in flower symmetry evolution revealed through phylogenetic and developmental genetic advances

2014 ◽  
Vol 369 (1648) ◽  
pp. 20130348 ◽  
Author(s):  
Lena C. Hileman
Keyword(s):  
Bilateral Symmetry ◽  
Radial Symmetry ◽  
Plant Evolution ◽  
Flowering Plant ◽  
Developmental Studies ◽  
Developmental Genetic ◽  
Evolutionary Transitions ◽  
Flower Symmetry ◽  
Molecular Phylogenetic ◽  
Developmental Programme

A striking aspect of flowering plant (angiosperm) diversity is variation in flower symmetry. From an ancestral form of radial symmetry (polysymmetry, actinomorphy), multiple evolutionary transitions have contributed to instances of non-radial forms, including bilateral symmetry (monosymmetry, zygomorphy) and asymmetry. Advances in flowering plant molecular phylogenetic research and studies of character evolution as well as detailed flower developmental genetic studies in a few model species (e.g. Antirrhinum majus , snapdragon) have provided a foundation for deep insights into flower symmetry evolution. From phylogenetic studies, we have a better understanding of where during flowering plant diversification transitions from radial to bilateral flower symmetry (and back to radial symmetry) have occurred. From developmental studies, we know that a genetic programme largely dependent on the functional action of the CYCLOIDEA gene is necessary for differentiation along the snapdragon dorsoventral flower axis. Bringing these two lines of inquiry together has provided surprising insights into both the parallel recruitment of a CYC -dependent developmental programme during independent transitions to bilateral flower symmetry, and the modifications to this programme in transitions back to radial flower symmetry, during flowering plant evolution.

Inversion of the Dorso-ventral Axis in Amphibian Embryos by Unilateral Restriction of Oxygen Supply

Development ◽  
1958 ◽  
Vol 6 (3) ◽  
pp. 486-490
Author(s):  
S. Løvtrup ◽  
A. Pigon
Keyword(s):  
Oxygen Supply ◽  
Nile Blue ◽  
Bilateral Symmetry ◽  
Radial Symmetry ◽  
Point Of View ◽  
Low Permeability ◽  
Grey Crescent ◽  
Protein Coat ◽  
Amphibian Embryos

According to the hypothesis advanced by Løvtrup (1958) the supply of oxygen is one of the factors responsible for the determination of bilateral symmetry in amphibian embryos. The protein coat covering the outside of the egg is known to have a very low permeability (Holtfreter, 1943), and it was suggested in the hypothesis that the formation of the grey crescent consists in a stretching of this coat by which the permeability is increased (cf. the work of Dalcq & Dollander (1948) and of Dollander & Melnotte (1952) on permeability of Nile blue), in this way the radial symmetry of the egg is changed to a bilateral symmetry from a metabolic point of view. As a consequence of the increase in permeability those oxidative, energy-supplying processes which are associated with gastrulation are enabled to proceed at a higher rate at one side of the egg.

scholarly journals Body Plan of Sea Urchin Embryo: An Ancestral Type Animal

2001 ◽  
Vol 18 (6) ◽  
pp. 757-770 ◽  
Author(s):  
Koji Akasaka ◽  
Hiraku Shimada
Keyword(s):  
Sea Urchin ◽  
Body Plan ◽  
Sea Urchin Embryo ◽  
Ancestral Type

Triassic roots of the amphiastraeid scleractinian corals

2001 ◽  
Vol 75 (1) ◽  
pp. 34-45 ◽  
Author(s):  
Ewa Roniewicz ◽  
Jarosław Stolarski
Keyword(s):  
Type Species ◽  
Adult Stage ◽  
Bilateral Symmetry ◽  
Radial Symmetry ◽  
Scleractinian Corals ◽  
Upper Triassic ◽  
Phylogenetic Status ◽  
Phylogenetic Hypotheses ◽  
First Time

The Early Carnian (Upper Triassic) phaceloid coral originally described by Volz (1896) asHexastraea fritschi, type species ofQuenstedtiphylliaMelnikova, 1975, reproduced asexually by “Taschenknospung” (pocket-budding), a process documented herein for the first time. This type of budding is recognized only in the Amphiastraeidae, a family thus far recorded only from Jurassic-Cretaceous strata. Similar to amphiastraeids,Quenstedtiphyllia fritschi(Volz, 1896) has separate septal calcification centers and a mid-septal zone built of serially arranged trabeculae. The most important discriminating characters of the new amphiastraeid subfamily Quenstedtiphylliinae are one-zonalendotheca and radial symmetry of the corallite in the adult stage (in contrast to two-zonal and bilateral symmetry in the adult stage in Amphiastraeinae).Quenstedtiphyllia fritschishares several primitive skeletal characters (plesiomorphies) with representatives of Triassic Zardinophyllidae and, possibly, Paleozoic plerophylline rugosans: e.g., thick epithecal wall and strongly bilateral early blastogenetic stages with the earliest corallite having one axial initial septum. To interpret the phylogenetic status of amphiastraeid corals, we performed two analyses using plerophylline rugosans and the solitary scleractinianProtoheterastraea, respectively, as the outgroups. The resulting phylogenetic hypotheses support grouping the Zardinophyllidae with the Amphiastraeidae in the clade Pachythecaliina (synapomorphy: presence of pachytheca). Taschenknospung is considered an autapomorphy for the Amphiastraeidae. This study is the first attempt to analyze the relationships of the Triassic corals cladistically.

scholarly journals Fossils from South China redefine the ancestral euarthropod body plan

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Cédric Aria ◽  
Fangchen Zhao ◽  
Han Zeng ◽  
Jin Guo ◽  
Maoyan Zhu
Keyword(s):  
South China ◽  
Phenotypic Variability ◽  
Morphological Diversity ◽  
Body Plan ◽  
External Morphology ◽  
Evidence Based ◽  
Early Cambrian ◽  
Neural Tissues ◽  
The Common ◽  
Bayesian Phylogeny

Abstract Background Early Cambrian Lagerstätten from China have greatly enriched our perspective on the early evolution of animals, particularly arthropods. However, recent studies have shown that many of these early fossil arthropods were more derived than previously thought, casting uncertainty on the ancestral euarthropod body plan. In addition, evidence from fossilized neural tissues conflicts with external morphology, in particular regarding the homology of the frontalmost appendage. Results Here we redescribe the multisegmented megacheirans Fortiforceps and Jianfengia and describe Sklerolibyon maomima gen. et sp. nov., which we place in Jianfengiidae, fam. nov. (in Megacheira, emended). We find that jianfengiids show high morphological diversity among megacheirans, both in trunk ornamentation and head anatomy, which encompasses from 2 to 4 post-frontal appendage pairs. These taxa are also characterized by elongate podomeres likely forming seven-segmented endopods, which were misinterpreted in their original descriptions. Plesiomorphic traits also clarify their connection with more ancestral taxa. The structure and position of the “great appendages” relative to likely sensory antero-medial protrusions, as well as the presence of optic peduncles and sclerites, point to an overall homology with the anterior head of radiodontans. This is confirmed by our Bayesian phylogeny, which places jianfengiids as the basalmost euarthropods, paraphyletic with other megacheirans, and in contiguity with isoxyids and radiodontans. Conclusions Sklerolibyon and other jianfengiids expand the disparity of megacheirans and suggest that the common euarthropod ancestor possessed a remarkable phenotypic variability associated with the externalized cephalon, as well as endopods that were already heptopodomerous, which differs from previous hypotheses and observations. These animals also demonstrate that the frontalmost pair of arthrodized appendage is homologous between radiodontans and megacheirans, refuting the claim that the radiodontan frontal appendages evolved into the euarthropod labrum, and questioning its protocerebral identity. This evidence based on external anatomy now constitutes a solid benchmark upon which we should address issues of homology, with the help of carefully examined palaeoneurological data.

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