Phylogenetic status of Peripatus

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  • Vikas Kumar

    Apr 9th, 2022

Systematically Onychophora presents a unique position: • The characters of Onychophora have made it most interesting from the point of view of evolution. It is an oldest terrestrial group which probably originated from some marine ancestors. • It has attained a number of features for terrestrial life, i.e., internal fertilization, viviparity, semi-solid excretory product, less permeable skin, etc. But at the same time the structure of spiracles speaks about its limitation on land life and thus shows its primitiveness. • The resemblances with annelids are probably the examples of convergence. Onychophorans have a mixture of morphological characteristic features which make them effectively cross between the Annelid worms and the Arthropods. But our modern understandings suggest they do not represent a missing link between the annelids and the arthropods. • Presence of variously developed specialized characters in Onychophora, such as trachaea with open spiracles and the origin of jaws do not support the above view that Onychophores represent a missing link. Instead, like the Tardigrades they are considered as a separate line of evolution and arose independently from some forgotten ancestor. • Again the common characteristic features of Onychophora regard a common relative to annelids and arthropods. Hence, it is regarded as a living connecting link between two phyla and it is undoubtedly an ancient form but not an ancestor of arthropods. • Kaestner (1967) has stated that the Onychophora probably represents an early lateral branch of the evolutionary line terminating in the arthropods. Peripatus are also called living fossils because they truly represent archaic animals and have changed little in their body shape for about 500 million of years. • A cladistic analysis which places the Onychophora in an intermediate position between the Polychaeta and the Tardigra-Arthropoda clade. The current view is that the Onychophora represent a sister group to the Arthropods on the basis of morphological, palaeontological and molecular data. • According to Marshall and Williams (1972)-Onychophora can be rightly described as an aberrant arthropods or highly modified annelids and can be placed all the species under twelve genera of Onychophora in a separate subphylum “Onychophora” under the phylum Arthropoda. But absence of jointed chitinons exoskeleton and jointed segmental appendages do not support the inclusion of Onychophora within Arthropoda. • Some peculiar features of Onychophores which support neither annelids nor arthropods, and demand a separate phylum status. Ruppert and Barnes (1994) pass the remark that Onychophorans are not usually considered arthropods rather a phylum animals closely related to arthropods.


Vikas Kumar

Vikas Kumar

Dr. Vikas did Masters, M. Phil. & Ph.D. from Delhi University. He was one of the gold medalists in the university during Masters in Zoology. He has published many research papers in drug designing & development. He is Assistant Professor in the University of Delhi. He believes in educating and not just teaching his students and enable them by inculcating scientific temperament to solve challenges in the field of Animal sciences.