CHAPTER XIX 

 PHYLUM ARTHPtOPODA (CONT'D) 



ONYCHOPHORA AND MYRIAPODA 



(By Vasco M. Tanner, Brigham Young University) 



Onychophora 



An interesting group of arthropods, now considered as the class 

 Onychophora, is restricted to the more tropical and semitropical 

 regions of the earth south of the Tropic of Cancer. These primitive 

 nocturnal forms, according to Austin H. Clark, are found in areas 

 that vary in annual temperature from 50° to 80° P.; in fact, most of 

 the species are confined to habitats in which the temperature does 

 not vary beyond the limits 60° to 70° F. 



The onychophores are characterized as soft-bodied, wormlike, ter- 

 restrial forms with internally segmented bodies. The body may be 

 divided into a head and abdomen. On the head is one pair of an- 

 nulate antennae and a pair of jaws. The body bears many pairs of 

 legs which are not distinctly jointed, but are provided with trans- 

 verse pads and apical claws. Kespiration is by means of tracheae 

 which communicate with spiracles that are, in some species, arranged 

 in rows on the body. The excretory system consists of nephridia 

 arranged in pairs in the body segments and opening to the outside 

 by a pore at the base of the fourth and fifth legs. The genital organs 

 discharge at the posterior end of the body. The nervous system is 

 ventral, consisting of separate longitudinal nerve cords connecting 

 a number of ganglia. A pair of eyes is located at the base of each 

 antenna. The body wall consists of an unsegmented dermomuscu- 

 lar covering. 



In commencmg on the ancestry of the Onychophora, Prof. J. W. 

 Folsom has the following to say: "Onychophora, as represented by 

 Peripatus, are often spoken of as bridging the gulf that separates the 

 Insecta, Chilopoda and Diplopoda from the Annelida. Peripatus 

 indeed resembles the chaetopod Annelids in its segmentally arranged 

 nephridia, dermomuscular tube, coxal glands and soft integument, 

 and resembles the three other classes in its tracheae, dorsal vessel with 

 paired ostia, lacunar circulation, mouth parts, and salivary glands. 

 These resemblances are by no means close, however, and Peripatus 



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