Reproductive biology

Female onychophorans are attracted to males by pheromonal secretions extruded from the males' crural glands. Reproduction takes place in an extremely curious manner. In some species, the males deposit packets of sperm (spermatophores) directly into the genital opening of the female, but in other species the spermatophores are placed somewhere on the body of the female. The skin tissue then collapses where the spermatophores are deposited, and the sperm migrate into the female's body, where they penetrate the ovaries to fertilize the eggs, or are stored for future use in paired sperm receptacles. Stored sperm remains viable for many months.

In some Australian species, the males place their sper-matophores on their heads like tiny trophies in readiness to present them to a female. Some species have developed elaborate structures on their heads, including spikes, spines, hollow stylets, pits, and depressions, to either hold the sperm or assist in its transfer to the female. Mating has been observed in only a few species.

Embryonic development is extremely diverse. Some species lay large, yolk-filled eggs, while others retain yolky eggs within the female until they are ready to hatch. Some other species have small eggs without a yolky food source, and the young are retained in the body and obtain nourishment from the mother's body in a manner similar to that of placental mammals. In all species, the young are fully developed when born and, apart from lacking complete pigmentation, look like miniature adults. There is no parental care and the young forage independently soon after birth. Some species appear to give birth throughout the year, but seasonality has been recorded for other species.

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