Kleptocnidy, or nematocyst sequestration, is the process whereby organisms acquire and make use of cnidocytes of digested prey. Sequestered cnidocytes are known as kleptocnidae, and are used for defense or to capture prey. Sea creatures preyed on for their cnidocytes include jellyfish, hydroids, sea anemones, corals, and other cnidarians with cnidocytes. [1]
The word Kleptocnidy comes from the Ancient Greek words κλέπτης (kleptés), "to steal", and κνίδη (knídē), "sea nettle" – the word used for the phylum Cnidaria, which contains all animals with cnidocytes. [2]
Kleptocnidy occurs as a specialized form of phagocytosis, whereby cells engulf cnidocytes without triggering them. [3]
Haeckelia comb jellies pass cnidocytes from their stomach down tentacular canals, to line their tentacles for use in prey capture. [1] [4]
Most flatworms capable of kleptocnidy have cells called cyst cells or cnidophages to deliver nematocysts from their digestive tract to their epidermis. [1]
Nudibranchs capable of kleptocnidy have branched digestive glands and cerata that are tipped with cnidosacs, such that cnidocytes are passed directly from digestion to their cnidosacs for use. To protect from nematocysts firing in their digestive tract, Aeolid nudibranchs have a hard cuticle lining their esophagus and have a mucus that chemically inhibits discharge and provides an additional barrier. [5] Nudibranchs use the cnidocytes for defense and prey capture. [3] [5]
It has evolved independently in various sea creatures, including Ctenophora, Acoelomorpha, Platyhelminthes, and Mollusca. Below is a table outlining the various occurrences of Kleptocnidy, given by Goodheart et al. [1]
| Phylum | Order | No of Species | Inferred No of Origins |
|---|---|---|---|
| Ctenophora | Cydippida | 3 | 1 |
| Acoelomorpha | Acoela | 1 | 1 |
| Platyhelminthes | Catenulida | 1 | 6–13 |
| Macrostomorpha | 12 | ||
| Proseriata | 5 | ||
| Prolecithophora | 4 | ||
| Polycladida | 9 | ||
| Rhabdocoela | 1 | ||
| Mollusca | Nudibranchia | ~600 | 1–2 |
Haeckelia is the genus in Cydippida that performs kleptocnidy. Childia dubium is the species in Acoela to do so. Aeolidida is the primary clade in Nudibranchia that perform kleptocnidy, though there are a few in the unplaced genus Hancockia that can as well. Kleptocnidy occurs in a range Platyhelminthes. [1] [5]