Macro-morphological variation among cryptic species of the moon jellyfish, Aurelia (Cnidaria: Scyphozoa)

Morphological variation in qualitative and quantitative features is compared among species of Aurelia defined a priori using molecular criteria. Macromorphological features were more numerous than previously implied (28 cf. 17), most were variable (26 of 28), and all species were morphologically distinguishable using univariate, multivariate and phylogenetic statistics. However, due to discrepant morphological descriptions, Aurelia spp. 3, 4, and 6 could not be assigned reliably to any previously described species, and there are still insufficient macro-morphological characters and variation to reconstruct a statistically robust phylogeny for even the 12 known species of Aurelia. Yet it is shown that Aurelia aurita is most likely endemic to the boreal Atlantic Ocean and northern European seas, Aurelia labiata is neither as morphologically diverse nor widespread as recently described, and the circumglobal Aurelia sp. 1 is probably introduced across much of its range. Electronic Supplementary Material is available for this article if you access the article at http://dx.doi.org/ 10.1007/s00227-003-1070-3. A link in the frame on the left on that page takes you directly to the supplementary material. Introduction Traditional taxonomic publications on species of the moon jellyfish, Aurelia Péron & Lesueur, have provided little consensus. In 1910, A.G. Mayer noted that ‘‘a dozen species’’ ofAurelia had been described although he recognized only 13 varieties in ‘‘3 reasonably well-defined types’’, A. aurita Linnaeus, A. labiata Chamisso and Eysenhardt, and A. solida Browne, on the basis that the morphological ‘‘distinctions between many of the ‘species’ are not well ascertained, and there are numerous varieties of local races’’ (Mayer 1910). By the 1960s, however, ‘‘about 20 species’’ of Aurelia had been described (Kramp 1968) although Kramp (1961) recognized just seven, A. aurita, A. coerulea von Lendenfeld, A. colpota Brandt, A. labiata, A. limbata (Brandt), A. solida, and Aurelia spp. [no authority], suggesting that ‘‘it is better to retain too many species than to unite species whose identity cannot be stated with certainty, thereby causing confusion in zoogeographical discussions’’. Yet, within a few years, Kramp (1965) discussed just five types and subsequently recognized only two species, a circumglobal, almost cosmopolitan, A. aurita and an arctic A. limbata (Kramp 1968). His reasons were that ‘‘certain structural features ... emphasized as characteristic of certain forms ... may frequently be observed in complicated combinations, even within one and the same individual’’ and that others ‘‘may be changed during preservation’’, are ‘‘variable within one and the same population’’, or ‘‘dependent on the age and developmental stage of the individual’’ (Kramp 1968). The occurrence of just two species of Aurelia was accepted until the late 1990s (Russell 1970; Larson 1986, 1990; Arai 1997) despite the publication of allozyme data indicating at least three distinct forms of A. aurita (Zubkoff and Lin 1975). Additional protein electrophoretic data, coupled with morphological analyses, in the mid-1990s strengthened the evidence for cryptic species of A. aurita within the Pacific Ocean (Greenberg et al. 1996) and, soon after, one of Marine Biology (2003) 143: 369–379 DOI 10.1007/s00227-003-1070-3