A retracted live green hydra (Phylum Cnidaria, class Hydrozoa, genus Hydra) tentacle (cnida) showing multiple nematocysts that are still embedded in the cnidocytes that formed them. Nematocysts of this species have a bulb-shaped base that connects to a narrow barbed top, from which a long thin filament extends many times the length of the nematocysts base. In this image the nematocysts are all still embedded in the cnidocytes, clear cells lining the tentacle that produce nematocysts. Two nematocysts are focused on in this image. Seen at approximately 1,000x magnification under a light microscope with no staining or artificial coloring.