| Hydroids comprise an important marine benthic group,dwelling attached to hard substrata throughout the oceans of the world.Sertulariidae Lamouroux,1812(Hydrozoa: Leptothecata)is the largest family in the phylum Cnidaria,comprising more than 600 nominal species.Recent molecular data indicate that it is a highly advanced group in the Medusozoa.Since its monophyly is insufficiently supported,it has been proposed to be divided into several families.In the present study,an integrative approach combining morphological,molecular and paleontological data is introduced to study the diversity and evolution of this family,by investigating approximately 1700 extant and fossil specimens collected during more than thirty Chinese,American and German scientific research expeditions on the Arctic Ocean,Bering Sea,Chinese Seas,Indian Ocean and the Antarctic Ocean.In the course of the study:1)One hundred and eleven species(containing doubtful species)were described and illustrated;thirty species are newly sequenced with mitochondrial and/or nuclear markers;a family sensu stricto(Sertulariidae sensu stricto Maronna,2016)and two genera(Sertularia Linnaeus,1758,Fraseroscyphus Boero & Bouillon,1993)were revised,a genus(Serta Stechow,1920)was revalidated,fifteen new taxa were proposed,including a new family(Diphasidae fam.nov.),eight new genera(Bicaularia gen.nov.,Coronaria gen.nov.,Nudicaulia gen.nov,Opposilaria gen.nov.,Pseudosertularia gen.nov.,Simplilaria gen.nov.,Xingyurella gen.nov.,Zhainaria gen.nov.),six new species(Xingyurella xingyuarum sp.nov.,Sertularella undulata sp.nov.,Thuiaria orientalis sp.nov.,Nudicaulia pluma sp.nov.,Sertularia xuelongi sp.nov.,Sertularia sinensis sp.nov.),and thirty-one new taxonomy combinations.2)After re-examination of the type material of a fossil species from Cambrian China,high morphological affinity of the fossil species with the extant Sertulariidae genus Diphasia was found.This may indicate that the advanced hydroid group Sertulariidae has already appeared in the Cambrian.Combining other hydroid fossil records and Medusozoan moleuclar phylogenetic lineages,the estimated appearance of the hypothetical Medusozoan ancestor took place at least before 830 Ma,earlier than previously thought(570 Ma).This represents a significant impact in concepts of Medusozoa evolutionary history.3)Based on evolutionary correlation analyses of molecular phylogenetics of nearly 90 sertularids and 50 morphological characters,a number of hypotheses regarding morphological characters and distribution could be set up.Simple and complex hydrocauline branching patterns were tracked repeatedly in major monophyletic groups.While convergent evolutionary characters,such as hydrothecae arranging in multiple longitudinal rows or specialized female gonothecal protection structures,were found in different main clades,several synapomorphies were found within the main groups.Some groups are only distributed in the Arctic Ocean and other boreal seas or only in Antarctic Ocean.A few widely distributed species regain the medusa stage.These findings will contribute to the first systematic monograph(s)on hydroids from Chinese Seas,and/or Chinese National Polar Scientific Expeditions.The paleontological findings will serve as new basis for the reconstruction of Medusozoan,Cnidarian or Metazoan evolutionary history,the data generated in the study represent generous background data for biodiversity research,monitoring,education and conservation in the investigated regions. |
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