Research On Developmental Biology Of Scyphozoan: Quadrapyrgites From The Cambrian Fortunian Stage

The Cambrian explosion began in the Fortunian Stage is a critical period for the evolution of the life of the earth.And it serves as a link between Ediacaran biota and Chengjiang fauna.Many fossils of Lagerst?tte is found from Cambrian Fortunian Stage at the northern edge of Yangtze Platform.The region is one of the best in the world,with its rich fossil and clear phosphorous stratum.The precious three-dimensionally phosphatized specimens have important research meaning for the origin and evolution of early life.And it is the basis for biostratigraphic comparison at the pre-trilobites-era of Early Cambrian.This paper mainly describes Lagerst?tte and soft-bodied Quadrapyrgites.This paper focuses on developmental biology of the Quadrapyrgites from the early Cambrian in southern China.We found two embryos at a later stage of embryonic development from Cambrian Fortunian Stage at the northern edge of Yangtze Platform.Observational studies showed that the ectoderm was folding inward forming the gastrulation.During the gastrulation the ectoderm was folding inward forming an archenteron-like structure resulting in the development of the initial tetramerous lobes with dense radial folds.At a later stage the embryos with tetramerous lobes of Quadrapyrgites formed 12 retracted lobes.The resulting hatchlings always exhibit 12 apertural lobes and a closed oral end.The embryos exhibited a crenulated surface except for the smoother aboral part that later developed into the pyramidal apex of hatchlings.Then,we present a description on the growth pattern and post-embryonic development of Quadrapyrgites.The growth zone of Quadrapyrgites is situated at the oral end,and new terminal lobes are generated within the oral aperture.The terminal lcrestsobes are first in control of the opening and closure of the tubes,and later transferred to be,thus elongating the tubes.The post-embryonic development is characterized by a one-by-one addition of crests on the post-embryonic tissue,and an ontogenetic sequence with crest number from 1 to 17 is reconstructed.During the ontogeny,the embryonic tissue remains stable in size and morphology.The oral aperture is the only opening of the tubes?The systematic positions of Quadrapyrgites is hot topics in palaeoembryology and evolutionary biology in recent years,but are still under debate.Quadrapyrgites was proposedto be the sister group of Olivooides because the comparable morphology and growth patterns.The preserved parts of Quadrapyrgites may represent the periderm which share great similarities with the periderm sheaths of coronate scyphozoans.So,it is proposed that Quadrapyrgites might be a coronate scyphozoan.The tubes of Olivooides and Quadrapyrgites may represent ephyrae and medusoid forms.From the analysis of life style and morphological function of Quadrapyrgites specimens we can see that there is no channel for material communication with the outside environment.Both the cone and tube are completely closed.The oral aperture might be the only opening of body.And we speculate that the Quadrapyrgites may be living on the bottom of the camp,and the pyramidal cone is the "attachment",which is fixed in the sand and mud base to avoid being washed away by the current.The terminal lobes is the tentacle of the larva.Two layer of zigzag-shaped lobes opening when predation.The water then passes through the internal "turbine" into the body,through the filtration of the nutrition tube,feeding the food from the nutrient canal to the nutrition organ.Finally,the waste is discharged through the mouth part.After further research,the following conclusions are drawn: Quadrapyrgites belongs to coronate scyphozoan of Cnidaria.The ectoderm of Quadrapyrgites was folding inward forming the gastrulation.The growth area is located at the mouth part,and has the growth pattern of overturning.The life style of Quadrapyrgites is benthic attachment life,and the oral aperture may be the only opening of the organism.