Large Parasitic Isopod

Overview

Anilocra physodes is a widespread ectoparasitic isopod commonly found attached to the external surfaces of various marine fish. These crustaceans are frequently observed clinging to the head, fins, or gill covers of their hosts, where they feed on blood.

Appearance

This isopod typically reaches lengths of 20 to 30 mm. Its segmented body consists of a distinct head with visible eyes, a seven-segmented thorax, and a six-segmented abdomen. It possesses seven pairs of legs, each ending in sharp, curved hooks that allow it to anchor firmly into the host's skin or flesh.

Biology & behavior

Anilocra physodes is a protandrous hermaphrodite, meaning individuals begin life as males and can transition into females as they grow. Typically, only one mature female is found on a single host fish at a time. While they are specialized parasites, they are not strictly host-specific and have been recorded on a wide variety of fish families, particularly sparids and labrids. Interestingly, some predatory fish have been observed consuming these isopods, effectively turning the parasite into a food source.