Relatively recent evolution of an unusual pattern of early embryonic development (long germ band?) in a South African onychophoran,Opisthopatus cinctipesPurcell (Onychophora: Peripatopsidae)
1995; Oxford University Press; Volume: 114; Issue: 1 Linguagem: Inglês
10.1006/zjls.1995.0016
ISSN1096-3642
Autores Tópico(s)Polar Research and Ecology
ResumoDuring embryonic development the process of segment formation in both families of the Onychophora, the Peripatidae and the Peripatopsidae, follows an essentially similar pattern with the exception of the South African peripatopsid, Opisthopatus cinctipes Purcell. In all other species in which development has been described, paired lateral halves of the embryo, separated by extra-embryonic ectoderm, develop as thickened bands on the surface of the blastoderm coincident with the appearance of the mouth and anus. The bands quickly differentiate paired segmental swellings with intersegmental grooves. The body elongates by proliferation from a posterior growth zone. During this process, presumptive mesoderm, located posteriorly in the early embryo, proliferates and moves anteriorly to form two lateral bands of mesodermal cells which segment during their forward growth into an anterior-posterior sequence of paired somites. In O. cinctipes the embryo elongates without any visible external or internal segment boundaries. In the elongating embryo only ectoderm and endoderm layers are present. Only after elongation has occurred are mesodermal somites formed. Allozyme analysis indicates that O. cinctipes diverged from the other South African genus Peripatopsis Pocock, with in the last 30 Myr.
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