Late postnaupliar development of Monstrilla sp. (Copepoda: Monstrilloida), a protelean endoparasite of benthic polychaetes

Abstract

Polychaete specimens from Hawaii were infected by the copepod Monstrilla. The development of these protelean parasites has remained unstudied for more than a century. Three postnaupliar endoparasitic stages were obtained: copepodids CIII, CIV, and CV, the latter stage found previous to and during emergence. Copepodid development, including the body and appendages (antennules, legs 1–4, caudal rami), is described and analyzed. The feeding tubes and the exiting from the host are also described. In light of the recently proposed inclusion of monstrilloids among caligiform copepods, it was found that monstrilloid copepodid development diverges from caligiforms and other copepod groups in: (1) the segmentation of the urosome at CIII, (2) the early formation of a genital complex, (3) early completion of swimming legs setation, at CIII; (4) delayed segmentation of rami of leg 3 at CIII (vs. the usual two-segmented pattern), (5) loss of one exopodal seta of leg 1 at CIV, (6) full development of leg 1 endopod vs. usually vestigial condition in caligiforms; (7) earlier segmentation of leg 4 rami, and (8) stable interstage (CIII–CV) setation pattern of legs 3 and 4. Overall, monstrilloid development appears to have unique characters and their phylogenetic relations deserve further study.

Keywords:

• parasitic copepods
• ontogenetic development
• crustacean parasites

Acknowledgments

Scanning Electron Microscopy (SEM) observations were performed using the equipment at facilities of the Universidad de Aguascalientes, Mexico. We appreciate the help and advice of Marcelo Silva-Briano and Araceli Adabache, who processed the specimens for SEM analysis. Luis F. Carrera-Parra (ECOSUR-Chetumal) kindly provided the color photographs of the monstrilloid copepod leaving the polychaete host. Rosa Ma. Hernández (ECOSUR-Chetumal) provided the catalog numbers of the Zooplankton collection at ECOSUR. The constructive comments by two reviewers are very much appreciated.