Large Parasitic Isopod – Nerocila armata

Nerocila armata is a species in the order of the Isopoda and thus belongs to the subphylum of the Crustacea. The Large Parasitic Isopod was first described in 1853 by Dana.

Isopode isopoda Nerocila armata - AsselFischassel Krebstiere Crustacea tauchen kanaren kanarische inseln atlantik atlantischer ozean
Large Parasitic Isopod – Nerocila armata


The colouration of Nerocila armata is grey to silver. The body is annularly segmented. At the bottom are seven legs with which it can hook itself to fishes.

The Large Parasitic Isopod can be larger than 2cm.

Habitat and Distribution

Nerocila armata lives on fishes. So far I have only seen it on Glasseye Snappers, but it also happens that it is found in the European Parrotfish or Lizardfish.

When diving in the Canaries we can often see the Large Parasitic Isopod. Especially if you look in columns for Glasseyes, one should find.

Its distribution area extends from Gabon, Congo, Senegal, South Africa to the Indian Ocean to Mauritius. Probably they are still more widespread, as well as the Glasseye.


As a young animal, Nerocila armata hooks to any fish. As adult animals, Isopoda are usually bound to certain species. So they leave their host as a young animal and look for the certain species of fish before they become adult. Then they stay permanently at their host.

They feed on the blood and tissue of the host, which can lead to the death of the host.

The Large Parasitic Isopod belongs to the family of the Cymothoidae. These are generally hermaphroditic, which change their sex in the course of their lives. This means that young animals are transformed into males and later to females. Females are able to deliver pheromones, which prevent males turning to females.


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