ABSTRACT
A recent accomplishment of biological oceanography is the discovery that the mesopelagic ocean has an extremely abundant fauna of large, delicate, gelatinous organisms (Figure 21.1). What makes this body plan so successful in the ocean’s interior? That it has been exploited by several phyla emphasizes its adaptive advantage. The classical large, gossamer, gelatinous phyla are the “jellies,” cnidaria and ctenophores (Matsumoto and Robison, 1992; Robison et. al., 1998), but recent exploration of the mesopelagic realm (200 to 1000 m) by both manned and unmanned vehicles has found other taxa, such as tunicates (larvaceans), siphonophores, and mollusks (pteropods), that exploit this life form by producing large feeding structures (Hamner and Robison, 1992; Hopcroft and Robison, 1999). The usual size of some of these delicate organisms ranges from about 0.3 to 3.0 m, but sonic imaging reveals some mid-water siphonophores over 30 m in length (Robison, 1993, 1995). These magnificent animals are never represented intact in the mangled specimens harvested by nets. Our discussion of gelatinous predators below pertains to mid-water siphonophores and the other, smaller, gelatinous organisms.
