Ökologie von Asterocheres lilljeborgi,eines auf Henricia sanguinolenta parasitisch lebenden Copepoden

Living specimens of Asterocheres lilljeborgi (Boeck, 1859) (Copepoda: Cyclopoida) were observed on the sea star Henricia sanguinolenta from the Gullmarfjord, Sweden. Copepodid stages as well as males and females live ectoparasitically on the sea star. They maintain a motile way of life and do not posses special adaptations of body form and extremity structure to the echinoderm host. A. lilljeborgi digests the skin of H. sanguinolenta extra-intestinally and sucks up the food by means of the siphon-shaped mouth. The intestine has caeca, which become increasingly branched during the development from copepodid stages to male or to female. The number of eggs is low, 7 to 9 in each egg sack. During copulation, the ventral sides of the genital segments of both male and female approach each other closely, thus facilitating transfer of spermatophores. All larger H. sanguinolenta of the Gullmarfjord are infested by A. lilljeborgi. Comparison between Scottomyzon gibberum and A. lilljeborgi shows that the female of S. gibberum has become more modified in structure and behaviour than the A. lilljeborgi female. In order to characterize the degree of parasitic life of the two species (both Cyclopoida siphonostoma) the term “parasitic” (not “semiparasitic” or “associated”) is suggested, because the nauplius larvae only are free living.