A nematocyst is a subcellular structure or
organelle
In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
containing extrusive filaments found in two families of
athecate dinoflagellate
The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
s (a group of
unicellular eukaryote
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
s), the
Warnowiaceae
The Warnowiaceae are a family of athecate dinoflagellates (a diverse group of unicellular eukaryotes). Members of the family are known as warnowiids. The family is best known for a light-sensitive subcellular structure known as the ocelloid, a hi ...
and
Polykrikaceae.
It is distinct from the similar subcellular structures found in the
cnidocyte cells of
cnidarian
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Their distinguishing feature is cnidocytes, specialized cells that th ...
s, a group of multicellular organisms including
jellyfish and
corals; such structures are also often called nematocysts (alternatively, ''cnidocysts'' or ''cnidae''), and cnidocytes are sometimes referred to as nematocytes. It is unclear whether the relationship between dinoflagellate and cnidarian nematocysts is a case of
convergent evolution or
common descent
Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...
, although molecular evidence has been interpreted as supporting an
endosymbiotic origin for cnidarian nematocysts.
In polykrikoids the nematocyst is found associated with another extrusive organelle called the
taeniocyst, a complex that has been described as
synapomorphic
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
for the
genus ''
Polykrikos
''Polykrikos'' (from Greek “poly” - many, and “krikos” – ring or circle) is one of the genera of family Polykrikaceae that includes athecate pseudocolony-forming dinoflagellates. ''Polykrikos'' are characterized by a sophisticated bal ...
''.
The full range of functional roles of the nematocyst is not well understood, but it has been observed to be involved in
prey capture and feeding.
References
{{reflist, 30em
Organelles
Dinoflagellate biology