Homology Of The Setae In Lepidocyrtinae(Collembola:Entomobryidae)

Collembolans,generally known as springtails,are small to median size of arthropods,with their number of individuals and species very abundant.They are widespread in various terrestrial ecosystems and one of the three major soil animals(nematodes and mites).Conpared to other hexapods or arthropods,Collembola is characterised by its specialised abdominal appendages,i.e.tenaculum(furca-holding organ)and jumping organ(furcula).Lepidocyrtinae belongs to the family Entomobryidae of the order Entomobryomorpha(Collembola).Its representative groups Lepidocyrtus and Pseudosinella are the largest two genus within Collembola.The identification of the species of the two genera is very difficult.Prior to the use of the dorsal chaetotaxy as the main distinguishing character,the traditional species identification of the subfamily are mainly based on claw morphology,number of eyes,color pattern,and structure of the mucro(distal part of the jumping organ complex).Szeptycki's work on the postembryonic development of tergal setae is fundamental for the species identification of Entomobryidae,making taxonomy more objective and reliable.Whereas,the setal homology of many species of Lepidocyrtinae are still difficult to distinguish,hindering the subsequent species classification,as well as phylogenetic analyses.Therefore,it is particularly necessary to carry out the research on the homoligization of setae by observing the postembryonic development of the species from Lepidocyrtus and Pseudosinella.The literature review part introduces the history of collembolan taxonomy,external morphology and body chaetotaxy,and illuminates the classification framework of the current four-order system.In addition,this chapter summarizes the research history of applying chaetotaxy in species identification,and stresses the importance of the study of the homology of chaetotaxy in the postembryonic development in Entomobryidae.This paper briefly describes the approach of species collection and breeding,specimen preparation,species identification,etc.,.I also provide the homology comparison criteria of setae.Through observing the postembryonic development of two representative species of Lepidocyrtus pallidus and Pseudosinella tumula,the dorsal cephalic,labial,and tergal chaetotaxy at the stage of 1st,2nd,3rd and adult are described in detail,and the homological transformation and quantitative changes of these chaetotaxy during individual development were analyzed.The study revealed that the shape and number of the primary setae(i.e.,setae present in newborn larvae)were relatively stable,mostly in the form of macrochaetae.Secondary chaetotaxy(setae appearing after the first instar)appeared from the 2nd instar larvae,and most primary setae were transformed into microchaetae,except for the anterior cephalic macrochaetae,leg and some fan-shaped setae on the botriothrical complexes.The 2nd instar larvae basically have the main chaetotaxic elements as the adult.The chaetotaxic changes during postembryonic development is basically the same for Lepidocyrtus pallidus and Pseudosinella tumula;the main differences are the number and shape of the botriothrical complexes,the number of eyes,and the number of macrochaetae on abdomen?.In addition,this study describes five 1st instar larvae in Lepidocyrtinae,including the antennae,the dorsal cephalic,the labium,the legs,the ventral tube,the furcula,and the dorsal body chaetotaxy.By comparing to the 1st instar chaetotaxy of other groups of the Entomobryidae,this study indicates that the chaetotaxy of the 1st instar larvae is almost identical in the arrangement and quantity.This study discusses the morphological differences of the first instar larvae of the subfamily,and analyzes the homology nomenclature systems of the chaetotaxy and the significance of homologization for taxonomy and phylogeny,filling the gaps in the research of larvae and setal homology of Lepidocyrtinae.