Tardigrada

Expression of NK cluster genes in the onychophoran Euperipatoides rowelli: implications for the evolution of NK family genes in nephrozoans

“…It has been hypothesized that such breakups of gene clusters are correlated with rapid modes of embryogenesis, possibly due to the loss of temporal collinearity and corresponding regulatory mechanisms in these taxa [ 63 ]. Since tardigrades also show rapid embryonic development (4–5 days in H. exemplaris [ 67 ]), this might be indeed due to the disintegrated homeobox clusters in these animals.…”

“…Library preparation and assembly of the embryonic transcriptomes from the onychophoran E. rowelli and the tardigrade Hypsibius exemplaris were performed as described previously [ 121 , 122 ]. The latter species was commonly referred to as “ Hypsibius dujardini (Doyère, 1840)” in the literature (e.g., [ 51 , 67 , 122 – 126 ]), but it was described recently [ 127 ] as Hypsibius exemplaris Gąsiorek et al, 2018. To identify the expressed homologs of NK homeobox genes in onychophorans and tardigrades, the transcriptome libraries of E. rowelli and H. exemplaris were screened by local tBLASTx searches [ 128 ].…”

External morphogenesis of the tardigradeHypsibius dujardinias revealed by scanning electron microscopy

“…Tardigrades generally undergo direct development and therefore lack true larval stages, that is, the juvenile hatchlings have a similar body shape as the adults and do not undergo any drastic metamorphoses (Bertolani, Grimaldi de Zio, D'Addabbo Gallo, & Morone de Lucia, ; Gross et al, ). However, the term “larva” has been applied to many heterotardigrade species that exhibit postembryonic development, where juveniles often possess a different number of digits than adults or lack a functional gonopore and/or anus (Bertolani et al, ; Hansen et al, ; Nelson et al, ).…”

“…Despite recent progress, competing hypotheses persist regarding several developmental processes (Gross, Treffkorn, & Mayer, ), for example whether mesoderm arises via enterocoely (Gabriel et al, ; Marcus, ; von Wenck, ) or schizocoely (Hejnol & Schnabel, ), and whether early cleavages are determinate (Gabriel et al, ) or indeterminate (Hejnol & Schnabel, ; Marcus, ; von Wenck, ); while other aspects have not been sufficiently detailed, such as the development of extracellular structures (for example, cuticular elements) and other external features. Scanning electron microscopy (SEM) can be a very effective method to clarify such questions and has already provided valuable insights into the embryonic development of many panarthropods, such as sea spiders (Machner & Scholtz, ), spiders (Liu, Maas, & Waloszek, ; Wolff & Hilbrant, ), amphipod crustaceans (Ungerer & Wolff, ), insects (Dorn & Hoffmann, ; Turner & Mahowald, ), and onychophorans (Walker & Tait, ).…”

Novel origin of lamin-derived cytoplasmic intermediate filaments in tardigrades

“…To clarify whether or not onychophorans and tardigrades possess cytoplasmic IF proteins, we analysed Illumina-sequenced transcriptomes of five distantly related onychophoran species and the freshwater tardigrade H. dujardini . Although this model tardigrade ( Gabriel et al, 2007 ; Gross et al, 2015 ) shows only a limited ability to tolerate desiccation (anhydrobiosis), it clearly survives immediate freezing (cryobiosis; see Video 1 ). Our analyses revealed only one putative IF protein transcript in each of the five onychophoran species but three in H. dujardini .…”