Gorgonolaureus muzikae sp. nov. (Crustacea: Ascothoracida) parasitic on a Hawaiian gorgonian,with special reference to its protandric hermaphroditism

Summary

Twenty-five specimens of a new ascothoracid parasite, Gorgonolaureus muzikae were found within cortical galls on specimens of a bathyal Hawaiian gorgonian, Placogorgia sp. These represent the first ascothoracid known from Hawaii. G. muzikae differs from its congener G. bikiniensis primarily in its larger size and details of setation. Five developmental stages are described and illustrated: the mature female, young female, late protander, protander, and nauplius. The protander is compared to species of Synagoga, and the characters distinguishing the two genera are specified. Sexuality in Ascothoracida is reviewed, and the life cycle of G. muzikae is reconstructed as follows: eggs and larvae are brooded within the carapace of a mature female; a bivalved, free-swimming male stage is postulated; after inseminating one or more established females it settles permanently on a host gorgonian; as the protandric male changes into a female, the carapace valves fuse and expand dorsally, the first and second antennae, thoracopods, penis, and abdomen become reduced, the dorsum of the second thoracomere becomes produced into a ‘horn’, and seminal receptacles appear in the thoracopods. The functional morphology of the second antennae, dorsal horn, and thoracopods is discussed, and it is suggested that G. muzikae may filter feed rather than be totally parasitic. The possibility that the large coxal setae represent vestigial epipods is discussed. Aspects of ecology, demography, and host specificity are briefly summarized. Wagin's (1976) biogeographical model of the provenance of Gorgonolaureus, based on outdated information, is rejected.