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SCYPHOZOANS AND CUBOZOANS SCYPHOZOANS (JELLYFISHES) Scyphozoan medusae are the familiar large jellyfishes more often seen from the surface than caught in plankton tows. Many of the roughly 200 currently recognized species reportedly have broad or even global distributions. The largest Atlantic jellyfish, Cyanea capillata, may reach a diameter of 2 m with tentacles exceeding 60 m in Arctic or boreal waters. Jellyfishes south of Cape Cod are usually much smaller but are important predators on estuarine and coastal zooplankton and exert a considerable influence on planktonic food webs when abundant. The typical scyphozoan life cycle includes both polyp and medusoid stages. Small, inconspicuous polyps (scyphistomae) live attached to the bottom and divide asexually by budding off a succession of 1 to 16 or more swimming ephyra stages (Fig. 13) that soon transform into young planktonic medusae. The medusae (i.e., scyphomedusae) represent the sexual stage of the life cycle and are either male or female, with gonads located in pockets in the mesoglea. Males shed their sperm into the water, but females of some local species retain the ripe eggs in the oral region where fertilization and early development occur. The resulting tiny, ciliated planula larvae are in the plankton only briefly before they settle to the bottom and begin the next generation of polyps. Polyps of many species can produce cysts resistant to unfavorable conditions and are important for overwintering (or oversummering in the case of Cyanea in the south). A few species, such as the open-water Pelagia noctiluca, lack a benthic polyp stage altogether. Jellyfishes move through the water using a pulsing movement of the bell as they trail their tentacles behind. The mesoglea’s stiffness returns the bell to its original position for the next stroke. Most local jellyfishes are feeble swimmers, but they can control their position in the water column, and some undertake regular vertical migrations. Statocysts arranged around the margin on the bell provide crucial information on which way is up. Often statocysts are found in association with primitive photosensors (ocelli). Temperate jellyfishes are predators that use their nematocysts to subdue a variety of primarily zooplankton prey. Several quite different feeding mechanisms are used. Species with long tentacles (e.g., sea nettles and lion’s mane jellies of the Order Semaeostomeae) capture prey with their tentacles and oral arms, which have powerful nematocysts. Often they swim up toward the surface and slowly sink down while feeding. Unwary zooplank- SCYPHOZOANS AND CUBOZOANS 111 ton and small fishes are caught by the passively drifting tentacles in this “ambush” style, subdued, and then transferred to the mouth and gastric cavity by the oral arms. While swimming, vortices created during bell pulsation serve both to propel the medusae forward and to carry smaller prey into the long, trailing tentacles and oral arms. The moon jelly Aurelia aurita employs its relatively small (. Accessed July 19, 2011. Calder, D. R. 2009. Cubozoan and scyphozoan jellyfishes of the Carolinian biogeographic province, southeastern, USA. Royal Ontario Museum Contributions in Marine Science 3:1–58. Hargitt, C. W. 1905. The medusae of the Woods Hole region. US Bureau of Fisheries 24:21–79. Kramp, P. L. 1961. Synopsis of medusae of the world. Journal of the Marine Biological Association of the United Kingdom 40:1–469. Larson, R. J. 1976b. Marine Flora and Fauna of the Northeastern United States: Cnidaria, Scyphozoa . NOAA Technical Reports NMFS Circ. 397, 1–17. 294 pp. Mayer, A. G. 1910. Medusae of the world. Vol. 3, The Scyphomedusae. Carnegie Institution of Washington Publications 109:499–735. Fig. 14. Pelagia noctiluca displays many of the anatomical features seen in the large jellyfishes . Ruffled oral arms and thin tentacles are common in one group but some others (e.g., Rhopilema verrilli) have robust and often fused oral arms and no tentacles. bell margin with lappets marginal cleft tentacle oral arm 114 IDENTIFICATION AND BIOLOGY OF COMMON ZOOPLANKTON Russell, F. S. 1970. The Medusae of the British Isles. Vol. 2, Pelagic Scyphozoa, with Supplement to the First Volume on Hydromedusae. Cambridge University Press, Cambridge. 284 pp. SUGGESTED READINGS Scyphozoa and Cubozoa Arai, M. N. 1997. A Functional Biology of Scyphozoa. Chapman & Hall, New York. 316 pp. Bayha, K. M., Dawson, M. N. 2010. New family of allomorphic jellyfishes, Drymonematidae (Scyphozoa , Discomedusae), emphasizes evolution in the functional morphology and trophic ecology of gelatinous zooplankton. Biological Bulletin 219:249–267. Bentlage, B., Cartwright, P., Yanagihara, A. A., et al. 2010. Evolution of box jellyfish (Cnidaria: Cubozoa), a group of highly toxic invertebrates. Proceedings...


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