Ontogeny of Rutiderma darbyi (Crustacea: Ostracoda: Myodocopida: Rutidermatidae) and comparisons with other Myodocopina

摘要

The carapaces and appendages of instars I-IV of Rutiderma darbyi Kornicker, 1983, are described and illustrated. The species has five growth stages including a single stage for the adult. A key to identification of stages by differences in appendage morphologies is presented. The morphologies of appendages at each stage of R. darbyi and R. arx Kornicker, 1992 are compared and found quite similar indicating that the two species develop in the same manner. The numbers of bristles on the 9th joint of the 2nd antenna of species of Rutiderma are useful for identifying the stage of development: 2 bristles on instar I, 3 on instar II, 4 on instar IV, and 5 on instar V. Natatory hairs are absent on bristles of the exopodite of the 2nd antenna of juveniles and present on adults; this distribution is useful for identifying them, and also indicates that the juveniles are restricted to the substrate. The presence of both a greater number of natatory bristles and a stouter protopodite on adult male rutidermatids indicate that the adult male is a stronger swimmer than the adult female. A similarity in the distribution of bristles on the 1st antennae and 6th and 7th limbs of instars I-III of R. darbyi (Rutidermatidae), which has five growth stages, and Skogsbergia lerneri (Kornicker, 1958) (Cypridinidae), which has six growth stages, suggests that the extra stage in species having six stages is added after instar III. The total number of bristles, claws, and teeth on appendages of each stage of R. darbyi (Rutidermatidae: Rutidermatinae), S. lerneri (Cypridinidae: Cypridininae), Gigantocypris muelleri Skogsberg, 1920 (Cypridinidae: Gigantocypridininae), and Tetragonodon rex Kornicker & Harrison-Nelson, 1999 (Philomedidae: Pseudophilomedinae), are compared. The rate of increase of the total number of bristles, claws and teeth at each stage is greater in the earlier stages of R. darbyi, S. lerneri, and T. rex, but greater in the later stages of G. muelleri, primarily because of a large increase in the number of bristles on the 7th limb of G. muelleri in the later stages.