Sting capsules (Cnidocysts)
All cnidarian species have sting capsules = cnidocysts. The name of the taxon Cnidaria is derived from this common character of all cnidarian species. In all cnidarian taxa the different cnidocyst types are an important taxonomic character used to identify and differentiate the species.
Cnidocysts have various functions. They are used for prey capture, defence or to attach to the ground. Each cnidocyst is a formation of a single cell which is eliminated and replaced by a new sting cell after use. During the explosion-like discharge of the cnidocyst a long tubule is released from the capsule. About 30 different capsule types can be distinguished by differences in the tubule shape (see e.g. Werner in Kaestner: Lehrbuch der speziellen Zoologie, Band 1, 2. Teil)
The contact of jellyfish with human skin can cause painful irritations (see Hoffmann et al. 2017).
In recent Bachelor theses the cnidocysts of selected cnidarian species have been described.
The results of the Bachelor thesis of Anneke Heins were published in September 2015. (see Heins et al. 2015)
Live-observation on the inconspicuous polyp generation of the upside-down jellyfish Cassiopea andromeda highlight their fascinating asexual reproduction strategies resulting in the offspring of either young polyps or tiny medusae (ephyrae). The examination of fresh tissues under 1000fold magnification provides new insights in the structures of the animals’ poisonous weapons for prey capture and defense: the stinging cells (cnidocysts). Focusing on the tubule shape and the spination of discharged cnidocysts discovers a higher diversity of cnidocyst types than previously assumed. Differences in abundance and size of specific cnidocyst types between five examined developmental stages indicates an adaptation to changing prey item preferences.