ИСТИНА

Monstrilloid copepods exhibit a protelean life cycle, comprising parasitic larval stages and free-living, nonfeeding adults. At present, around 180 nominal species in seven genera are known worldwide. Species descriptions are based exclusively on the adult planktonic stages, however, for many species only one sex, either the female or the male, is known so far. Although monstrilloid copepods can be abundant in the plankton, their endoparasitic larval stages have rarely been recorded or documented. Parasitic nauplii and copepodids display paired root-like absorptive processes which are presumably used for feeding on host fluids or predigested tissues; however, virtually nothing is known about the morphological adaptations related to the feeding process. The chalinid sponge Haliclona (Gellius) cymaeformis (Esper, 1806) and its symbiotic partner, the red macroalga Ceratodictyon spongiosum Zanardini, 1878 (Rhodophyta) are common on shallow reefs and reef flats in Okinawa, Japan, and it has recently been observed that there is a consistent association between H. cymaeformis and an as yet undescribed polychaete species belonging to Haplosyllis Langerhans, 1879 (Syllidae). Microscopical observations and dissection revealed that Haplosyllis sp. frequently contains endoparasitic stages of a monstrilloid copepod with infection rates varying between different sampling sites in Okinawa and ranging from 0.3 to 8%. More than 50 monstrilloid specimens at different stages of development were isolated from their host polychaetes. Several polychaete specimens were infected by two monstrilloid larvae which developed into either females or males or both. Live observations of copepodids both inside and outside the host were photographed and video-recorded, including the final moult into the adult stage in both sexes. Adults of both sexes were fixed for morphological identification while the different copepodid stages were examined using light microscopy, scanning electron microscopy (SEM) and micro-computed tomography (mCT). The latter non-destructive method was also employed to produce a high-resolution 3-D image showing the copepodid inside its host. The easy access to material of Haplosyllis sp. and its associated copepod stages offers the potential to design a more extensive case study that could lead to new insights into host-parasite interactions in general and the monstrilloid life cycle in particular, a topic that has not seen any significant advances since Malaquin’s (1901) seminal work.