Some aspects of segment formation and post‐placental development in Peripatus acacioi marcus and marcus (Onychophora)

Abstract

The surface morphology of the anterior-to-posterior sequence of segment formation in embryos of a viviparous neotropical onychophoran and aspects of post-placental development seen using scanning electron microscopy are described. When all the segments have formed and the walking legs have completed their elongation, the body surface becomes covered with an embryonic cuticle that does not exhibit the hydrofuge properties seen in the adult cuticle. As soon as the walking legs have reached their full length, barbed projections are formed at their distal extremities. These projections are extensions of single cells and are covered by the embryonic cuticle. Transmission electron microscopy reveals that the cells at the distal ends of the legs and their projections have many pinocytotic vesicles at their surfaces. The cytoplasm of these cells and their projections is rich in mitochondria, rough endoplasmic reticulum, glycogen, and granules of storage material. There are minor differences in the surface morphology of the projections found at the ends of the walking legs in embryos of Peripatus acacioi and those of Peripatus biolleyi. The projections and the embryonic cuticle persist thoughout postplacental development. The role of the projections in the uptake of material by the embryo from the uterus is discussed and the possible phylogenetic significance of these projections is suggested.

Head development in the onychophoran Euperipatoides kanangrensis with particular reference to the central nervous system

“…We regard this as further evidence for a terminally positioned mouth in the ground-plan of the arthropod clade. However, in the investigation of Peripatus acacioi, a viviparous species, no contribution to the lips from any frontal processes was reported (Walker and Campiglia, 1988). It would be of great interest, with further investigation on viviparous neotropical species, to learn if they have frontal processes and, if so, what is their developmental destiny.…”

Onychophora

“…Thus, like many arthropods, onychophorans show typical short germband development, since their body segments also arise in an anterior-toposterior progression (Figs. 4.6 , 4.7 , 4.8 , 4.9 , 4.10 , and 4.11 ;Kennel 1885Kennel , 1888Sedgwick 1887Sedgwick , 1888bEvans 1901 ;Manton 1949 ;Walker and Campiglia 1988 ;Campiglia and Walker 1995 ). The two reports (Walker 1992(Walker , 1995 of putative long germband development in Opisthopatus cinctipes are doubtful, as the thin linings of the dorsal coelomic compartments may have been overlooked in this species (see discussion by .…”

“…As the blastula increases in size via cell divisions, the blastocoel becomes more prominent. Specialized cells of the blastula, Embryos of successive developmental coil stages (staging according to Walker and Campiglia 1988 ). Note the stalk attached to the dorsal region of the embryo in ( E) .…”

“…4.6I ). ( I ) Embryo of early coil stage (staging according to Walker and Campiglia 1988 ). Note the coelomic cavities occupying most of the inner volume of the embryo, while endomesodermal cells continuously migrate in the posterior body region.…”

Neuronal tracing of oral nerves in a velvet worm—Implications for the evolution of the ecdysozoan brain

“…Despite detailed studies of the onychophoran head and associated structures, the segmental identity of the oral lip papillae remains unknown (e.g., Moseley, 1874; Sedgwick, 1885; von Kennel, 1888; Evans, 1901; Manton and Heatley, 1937; Pflugfelder, 1968; Walker and Campiglia, 1988; Eriksson and Budd, 2000; Walker and Tait, 2004; Mayer and Koch, 2005; Mayer et al, 2010; Oliveira et al, 2013). Our data on the morphogenesis of the mouth in the onychophoran E. rowelli revealed that the oral lip papillae of this species arise from three head segments.…”