A large flattened isopod clamped to the flank or the head of a living fish.
A flattened oval crustacean to about 4 cm, grey to silver-brown and segmented across the back, with seven pairs of legs ending in strong curved hooks. It is not attached to the substrate but to a fish, and it is normally seen fixed head-forward on the flank, behind the eye or on top of the head of a living animal that is swimming and feeding as usual.
The hooks hold it in place and it feeds on blood and tissue at the point of attachment. Cardinalfish, snappers, fusiliers and damselfishes are among the hosts recorded in the region. A fish that has carried one for a time shows a pale scar or an eroded patch of scales where the isopod sits, and scarred fish with no isopod present are commoner than occupied ones. Members of this family are protandrous, beginning as males and changing to female, and it is the large females that are visible on the host.
Anilocra belongs to the same family as the tongue-biters, and the difference is where the animal settles rather than what it looks like: this genus rides the outside of the fish, where the species that take the mouth attach at the base of the tongue and are visible only when the fish gapes. Recorded across the depth range that divers work, and found by watching fish rather than by searching the bottom.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.