Читать книгу Life in the Open Ocean - Joseph J. Torres - Страница 73

The Coronatae are deep‐dwelling jellyfish mainly inhabiting mesopelagic to bathypelagic depths, though some genera (Linuche, Nausithoe) are found in surface waters. Each has a characteristic deep furrow, the coronal groove, which divides the exumbrella into a central disc and a peripheral zone and gives the order its name (Figure 3.11). Below the coronal groove, the peripheral zone is divided into two subregions. First, the thickened deeply grooved pedalia, and below the pedalia and centered on the inter‐pedaliar grooves, the marginal lappets. The pedalia most often have a single, solid tentacle. Coronate medusae are heavily pigmented, usually deep burgundy in color, and most species have stiff noncontractile tentacles that are often held above the bell.

The life histories of coronate scyphomedusae are poorly known, largely because most of them sport a mesopelagic lifestyle. The best‐known life cycle is that of Nausithoe, which shows a typical scyphozoan pattern similar to that of the semaeostome Aurelia. It has a colonial scyphistoma stage that produces ephyrae by polydisk strobilation. The medusae reproduce sexually, producing a planula larva that settles to form a scyphistoma to continue the cycle. It has been speculated that the deeper‐dwelling genera such as Periphylla and Atolla use a strategy of direct development like that of the semeaostome Pelagia. In a direct‐development strategy, the planula develops directly into an ephyra, bypassing the scyphistoma stage altogether. Evidence in support of this hypothesis is the large size of the eggs in Periphylla and Atolla, which would facilitate the direct developmental strategy (Larson 1986 in Arai 1997).

Genera include Atolla, Linuche, Periphylla, Nausithoe, Stephanoscyphus, and Tetraplatia.

Figure 3.11 Coronatae. (a) The coronate scyphomedusa Periphylla (helmet jellyfish). (b) The coronate scyphomedusa Nausithoe (crown jellyfish).

Sources: (a) Adapted from Arai (1997), figure 1.5 (p. 7); (b) Redrawn from Mayer (1910), Vol. III, figure 352.