Читать книгу Life in the Open Ocean - Joseph J. Torres - Страница 63

The Cnidaria, or stinging jellies, include a bewildering array of groups ranging from aquarium favorites such as anemones to the infamous Portuguese man‐o‐war and to reef‐building corals, deep‐dwelling sea pansies, and sea pens. The focus in this book is the cnidarians that are large floaters and weak swimmers: the jellyfishes (the medusae) and the siphonophores. Both are important groups within the polyphyletic assemblage collectively known as the macrozooplankton. In turn, macrozooplanktonic species are important elements of the pelagic community.

The pelagic Cnidaria are particularly confusing because there are two types of medusae: the smaller and less complex hydromedusae and the larger scyphomedusae. Inshore, the scyphomedusae are far more noticeable to the casual observer and are seasonally well represented by species such as the moon jelly Aurelia and the scourge of Atlantic beaches, the sea nettle Chrysaora. Offshore, in the blue waters of the pelagic realm, the hydromedusae dominate numerically. Adding to the confusion is the fact that many, but not all, of the hydromedusae and scyphomedusae alternate generations from a sedentary, anemone‐like, polyp stage to a swimming medusoid form. The alternation of generations is sometimes termed “metagenesis.” It was the alternation of generations that captured the imagination of famous natural philosophers such as Cuvier, Lamarck, and especially Ernst Haeckel, who made siphonophores one of his favorite subjects for study.

Siphonophores are unfamiliar to most people not well acquainted with the open ocean because the animals are found predominantly offshore and are very delicate. Therefore, they are difficult to preserve or to view intact after capture. As a consequence, siphonophores have received limited study though they are common predators in the open ocean and especially in the deep sea.