Abstract:
Onychophora, or velvet worms, are rare invertebrates which display a wide range of reproductive adaptations and occupy a pivotal place in invertebrate taxonomy. Despite this, the life histories of many species are completely unstudied. Information which is available is often patchy and unsupported by published data. Many studies of onychophoran life histories are assumed to be based on the dissection of collected specimens; details of methods are rarely given in older studies. This study sets out to obtain information on the life history of Peripatoides novaezealandiae, one of the five described New Zealand species, by dissecting animals collected from a wild population. Between 50 and 150 P. novaezealandiae were collected from a site in the Tararua Ranges in the North Island of New Zealand, once a month from May 1995 to May 1996. Animals in the smallest length and weight classes were found at all times of the year, suggesting that births occur all year round. Twenty females and ten males were dissected from each month's sample. Widely varying numbers of sperm were found in the haemolymph of females, suggesting that sperm transfer takes place via the female integument, not the genital opening. Large numbers of sperm were seen in the haemolymph of several females in late Spring, Summer and Autumn, but this phenomenon was also noted at other times of the year. Large numbers of sperm were seen in the haemolymph of female P. novaezealandiae well before they had reached the size when females begin to produce embryos, suggesting that mating occurs well before reproduction begins. Females may continue to mate throughout life. Large numbers of sperm were seen in male reproductive tracts and female seminal receptacles at all times of the year. Embryos in some uteri were found to be at the same stage of development, in other uteri at somewhat different stages of development. Broods of embryos at all stages of development were found at all times of the year. Brood size is related to maternal length and weight, but embryo weight is not. The layers in the chitinous jaws of a small sample of animals were counted. Further work is needed to discover if this is an accurate method of aging velvet worms. The sex ratio of the combined samples was 0.75. Dissection of velvet worms collected from wild populations is a useful method for studying the life history, although variability between individuals may lead to mistaken conclusions regarding such things as reproductive seasonality and the mode of production of embryos, particularly if sample sizes are small.
