Dactylozoids

Dactylozoids are specialized zooids, or individual units, found in certain colonial marine invertebrates, most notably hydrozoans and some siphonophores. These zooids are primarily responsible for defense and prey capture. Their most distinguishing feature is the presence of nematocysts, which are stinging cells that can be discharged to paralyze or kill prey and deter predators. Morphologically, dactylozoids are typically elongated and slender, often trailing from the main body of the colony. They can vary in length and complexity depending on the species.

In hydrozoan colonies like hydroids, dactylozoids are often found interspersed with feeding zooids called gastrozooids. They can also be arranged in specialized clusters or branches. In siphonophores, which are highly complex colonial organisms, dactylozoids are part of a more specialized division of labor. They are typically associated with structures called tentilla, which are further extensions of the colony designed for capturing food. The mechanism of nematocyst discharge is a rapid, turgor-driven process that can be triggered by physical contact or chemical cues. The ability to sting makes dactylozoids crucial for the survival and feeding success of the entire colony.