title: Evolutionary meaning of non-synchronous medusa release and spawning in the most advanced bivalve-inhabiting hydrozoan, Eugymnanthea japonica.
abstract: Circadial spawning times of medusa of the bivalve-inhabiting hydrozoans Eugymnanthea japonica Kubota and Eutima japonica Uchida are confirmed to be morning (possibly sunrise) for the former species and night for the latter. Eugymnanthea, with small, short-lived, univoltine medusae, seems to have evolved from a form similar to Eutima japonica, with larger, longer-lived, multivoltine medusae; the morning spawning of medusae in Eugymnanthea may therefore be a newly evolved trait. Medusa release from polyps and spawning of medusae are not synchronous in Eugymnanthea japonica. This non-synchrony may represent an evolutionarily transitional state leading to the most advanced state, synchrony of these two reproductive events, as in certain other ephemeral hydrozoan medusae.
authors.affiliation: Seto Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University, Shirahama, Wakayama 649-2211, Japan. kubota.shin.5e@kyoto-u.ac.jp
authors.forename: Shin
authors.initials: S
authors.lastname: Kubota
mesh_terms: D000375:Aging; D000818:Animals; D005075:Biological Evolution; D049872:Bivalvia / Q000469:parasitology*; D005260:Female; D037402:Hydrozoa / Q000235:genetics* / Q000502:physiology*; D010063:Ovum / Q000502:physiology; D012098:Reproduction / Q000502:physiology