Segmental homologies of the maxilliped of some copepods as inferred by comparing setal numbers during copepodid development

Abstract

Segmental homologies of the maxillipeds of Longipedia americana, Coullana canadensis, Macrosetella gracilis, Hemicyclops adherens, and Troglocyclops janstocki are inferred by comparing segmental and setal numbers at CI, and changes in setal numbers during the copepodid phase of development, with published accounts of the calanoids Ridgewayia klausruetzleri and Pleuromamma xiphias. The unsegmented endopod of L. americana is a complex of 4 presumptive segments and the unsegmented endopod of C. canadensis is a complex of 3 presumptive segments. The endopod of T. janstocki appears to be 3-segmented, but the middle segment is a complex of 3 presumptive segments. Macrosetella gracilis has an unsegmented endopod of 2 presumptive segments; the distal segment is attenuate, forming a clawlike structure. Hemicyclops adherens has a 2-segmented endopod; the prominent, clawlike terminal structure on the maxilliped of the adult male is an attenuation of the distal endopodal segment. A homologous but more complex attenuation of that segment is present on the maxilliped of all of its copepodid stages including the adult female.