Five new subspecies of Mastigias (Scyphozoa: Rhizostomeae: Mastigiidae) from marine lakes, Palau, Micronesia

To some naturalists, Mastigias medusae in marine lakes, Palau, symbolize the evolutionary process (Faulkner, 1974). In the first scientific publication on marine lake Mastigias, Hamner & Hauri (1981) suggested that different long-distance horizontal migrations and different morphologies among populations isolated in three different lakes ‘might be considered of specific or subspecific importance’ yet, because one species of Mastigias from the lagoon probably colonized all three lakes, they cautioned that ‘differences may be only of local significance.’ Recent publications (summarized in the next paragraph and in Table 1) on the behaviour, morphology, and molecular genetics of the three populations studied by Hamner & Hauri (1981) plus two other marine lake populations and populations in the surrounding lagoon have increased our understanding of the nature and magnitude of these differences. Diel horizontal migrations show greater variety in direction and strength among marine lake populations than they do among populations in the lagoon (Dawson & Hamner, 2003; Table 1). Morphological variation is also greater among marine lake populations than it is among populations in the lagoon (Dawson, 2005a; Table 1). Indeed, morphological differences among lake populations exceed those recorded between many previously described nominal species of Mastigias (M. albipunctata Stiasny, 1920; M. andersoni Stiasny, 1926; M. gracilis (Vanhöffen, 1888); M. ocellatus (Modeer, 1791); M. pantherinus Haeckel, 1880; M. papua (Lesson, 1830); M. roseus (Reynaud, 1830); M. sidereus Chun, 1896) throughout the Indo-West Pacific in terms of, for example, the number of velar lappets, length of mouth arms, length of terminal clubs, number of adradial canal origins at the gastrovascular cavity, number of anastomoses among perradial canals, and the width of the subgenital ostia (Dawson, 2005a). However, DNA sequencing of mitochondrial cytochrome c oxidase subunit I (COI) shows mean pairwise sequence differences among lake populations (0.77%, SD 0.52%) and differences between lake and lagoon populations (0.52%, SD 0.42%) of Mastigias are similar in magnitude to intra-specific differences among Mastigias within the lagoon (0.26%, SD 0.19%; Dawson, 2005a; see also Dawson & Hamner, 2005). This result is corroborated by preliminary DNA sequencing of nuclear Internal Transcribed Spacer One (ITS1) which found differences of 3.39% (SD 0.72 %) between lagoon locations, 0.58% (SD 0.18%) between lake locations, and 1.74% (SD 1.22%) between lagoon and lake locations (Dawson, 2005a). These sequence differences are considerably less than those seen between medusae identified as Mastigias papua in coastal marine environFive new subspecies of Mastigias (Scyphozoa: Rhizostomeae: Mastigiidae) from marine lakes, Palau, Micronesia