Revised descriptions of the nematocysts and the asexual reproduction modes of the scyphozoan jellyfish Cassiopea andromeda (Forskal, 1775)

摘要

Our investigations on different developmental stages of the jellyfish Cassiopea andromeda (ForskAyenl, 1775) provide updated descriptions of nematocyst types and asexual reproduction modes, which were documented by drawings and high-resolution photographs. In contrast to previous studies that only described three types of nematocysts, we revealed five types: a-isorhizas, O-isorhizas, euryteles, large oval birhopaloids, and small lemon-shaped birhopaloids. Comparisons of undischarged and discharged capsules revealed significantly smaller capsule volumes (48-51 %) in the latter. We provide capsule lengths and widths ranges for each capsule type (undischarged) and developmental stage. We demonstrate that for most capsule types the calculated capsule volumes were positively correlated with the progressing development and increasing size of the five developmental stages, namely bud, polyp, strobila, ephyra, and medusa. O-isorhizas were only present in the latter three stages probably due to a change in diet related to a changing life style. Besides asexual reproduction by swimming buds and monodisc strobilation common in rhizostome Kolpophorae, we documented lateral polyp budding for the first time in this taxon. Our results demonstrate that cultivating living specimens facilitate detailed descriptions of nematocysts and reproductive modes in metagenetic cnidarians, which cannot be achieved by studies on preserved material.