Life history and population biology of the giant ostracod Leuroleberis zealandica (Baird, 1850) (Myodocopida)

A population of this large myodocopid ostracod was studied over 2 yr by random core-sampling of the medium sand bottom at Kaikoura, New Zealand. Leuroleberis zealandica (Baird) passes through seven instars, it is sexually mature only in the final instar and sexes were distinguishable from instar IV. Males and females were equally abundant except in the final instar when the morphologically distinct males were rarely found. The population consists of three cohorts at any one time and each cohort appears to split into fast- and slow-growing individuals during the sixth instar resulting in life times of 1.8–2.0 and 2.7–3.1 yr, respectively. Females produce only one brood of 37 eggs on average per life time that are carried throughout the 5–6 month development period during which there is no loss of embryos. Recruitment is discrete with most broods released in midsummer when the population density may exceed 350·0.1 m^?2. A second lesser recruitment may occur in early spring in some years. Hatched juveniles released from the female grow rapidly to instar IV within 6 months and, although size increments at each moult are proportionally similar, intermoult periods tend to increase with size with some variation according to seasonal growth rates. Instar life tables constructed from instar density data showed a large difference in the frequency of embryos initiating each cohort, very different mortalities at recruitment between cohorts, and that the mortality rates between instars I and VI of different cohorts appear to be independent of density. The biology of Leuroleberis is compared with the few published accounts of myodocopid biology. In addition, several aspects of the biology of myodocopids are reviewed. These include numbers of instars in different taxa, within-instar sexual size disparities, numbers of broods per female life time, egg and brood sizes in relation to adult female size in various taxa, and the question of post-adult moulting.