One of the many mysteries surrounding onychophorans, is why, despite their small body size, they have gestation periods that are as long as gestation in some mammals. Here we propose that the causes are infrequent feeding and the Mandatory Minimum Size model, according to which they must be born sufficiently developed to hunt their own food and survive adverse microclimates.
Agarwal, S. P., Khanna, N. D., Agarwal, V. K., & Dwaraknath, P. K. (1987). Circulating levels of estrogen and progesterone in female camel (Camelus dromedarius) during pregnancy. Theriogenology, 28(6), 849-859.
Gillooly, J. F., & Dodson, S. I. (2000). The relationship of egg size and incubation temperature to embryonic development time in univoltine and multivoltine aquatic insects. Freshwater Biology, 44(4), 595-604.
Havel, J. E., Wilson, C. C. & Hebert, P. D. N. (1989). Parental investment and sex allocation in a viviparous onychophoran. Oikos, 56, 224-232.
Monge-Nájera, J. (1994). Reproductive trends, habitat type and body characteristcs in velvet worms (Onychophora). Revista de Biología Tropical, 42(3), 611-622.
Monge-Nájera, J. (1995). Phylogeny, biogeography and reproductive trends in the Onychophora. Zoological Journal of the Linnean Society, 114(1), 21-60.
Sherbon, B. J., & Walker, M. H. (2004). A new species of Peripatopsis from South Africa, P. stelliporata, with observations on embryonic development and sperm degradation (Onychophora, Peripatopsidae). Journal of Zoology, 264(3), 295-305.