Colloblast

Colloblasts are special cells in comb jellies, also called ctenophores. These cells are found in the tentacles and help the comb jelly catch food.

Each colloblast has a cell called a collocyte that contains a spiral filament and other important parts.

When a comb jelly uses a colloblast, it shoots it from its tentacles to catch prey. Unlike the stinging cells of jellyfish, called cnidocytes, colloblasts shoot sticky glue to hold the prey.

Form and Function

Colloblasts were first described in 1844. They have two types of cells: a stalk with parts called the collosphere and collopod, and many cap cells. These cap cells put sticky granules on the collosphere.

When a colloblast is touched, it breaks away from the tentilla, part of the creature’s tentacles. When it touches prey, the granules burst and release sticky stuff. A spiral filament stays connected to the tentillum, holding the prey until it is eaten.

Variation and Occurrence

Colloblasts are found in all ctenophores except those in the order Beroida, which do not have tentacles, and the genus Haeckelia, which uses cnidocytes from cnidarian prey.

The biggest difference among ctenophore groups is the shape of the collosphere. The basal colloblast has a round collosphere, but the orders Cestida, Cydippida, and Lobata have a longer collosphere and no collopod, with the spiral filament attached directly to the collosphere. In these species, the spiral filament is often smaller or missing.

The round collosphere colloblast can be divided into five types based on the size and shape of its spiral filament and radii. Types I, II, and III, found on the front part of a small tentacle, are smaller and have fewer coils, while types IV and V, found on the end part, have more complex spiral filaments. The reason for this difference in shape is not known.