Cymothoidae Family of Isopods

Two Isopods of the Cynothoidae Family can be found in this website:

Phylogeny: Cymothoidae Isopods are members of the Cymothoidae Family.  They belong to the phylum Arthropoda, the class Malacostraca and the order Isopoda. The suborder Cymothoida is one of nine suborders in the order Isopoda, and the superfamily Cymothooidea is one of two superfamilies in suborder Cymothoida. The Cymothooidea superfamily contains nine families. Cymothoidae Family is large, with thirty-eight genera and three hundred eighty species.

Morphology: Cymothoidae Isopods are anthropods, indicative that they have jointed legs. Similar to terrestrial Pill Bugs, Sow Bugs, and Wood Lice, they are Isopods, which means that they have a rigid, segmented exoskeleton, two pairs of antennae, seven limbs, and five respiratory appendages. These Isopods have an unfused pleon of five free segments, compound eyes, and mouth parts that are modified for their parasitic behavior. Most specimens have a slightly twisted body that is believed to occur due to the result of their position relative to their host. Isopods in the Cymothoidae Family are among the largest Isopods reach a maximum of 7.5 cm (3.0 inches) in length.

Distribution: Cymothoidae Isopods are found in brackish, freshwater and marine environments. They live as ectoparasites on their host animal. Most are found in shallow water, but at least ten species are found at depths greater than 500 m (1,640 feet). Cymothoidae Isopods are found globally in temperate to tropical seas. Eighteen species from the Cymothoidae Family are found in Mexican waters.

Reproduction:  Cymothoidae Isopods are protandrous hermaphrodites. They all begin life as males and when the number of females in an area drops below a certain level the most mature males transition to females. The females are capable of releasing a pheromone that prevents the males in the vicinity form changing to females. Once they become female, they lose their ability to crawl and are committed for live to their current host. In some species, the females lose their ability to eat, and live off the stored energy that they built up as males. Reproduction is sexual with internal fertilization. The fertilized eggs are brooded in the female’s marsupium (brood pouch). The eggs hatch into free swimming larvae before setting onto a host fish.

Ecosystem Roles: Cymothoidae Isopods live on the outside of their host (ectoparasitism) primarily consuming the blood of the host. Adults are found primary attached to the gills, mouth, skin, or the base of fins of fish but they also can be found attached to invertebrates. Some are highly host specific, while others will attach to numerous different species. Some are ecologically specific, targeting types of fish based on lifestyle e.g. schooling fish, demersal fish, etc.; others are taxonomically specific, targeting only certain species. These isopods can significantly alter the life of their host by causing traumatic injury, scar tissue build up, reduced ability to flee predation, and secondary infections. As juveniles, Cymothoidae Isopods are free swimming and at this stage of life they are non-selective and will burrow into the skin of many types of fish. Once they become more mature, and find the correct, long term, host, they will attach to the new host and lose their ability to swim. Probably the most unique species in this family is the Tongue-eating Isopod, Cymothoa exigua. This species attaches to, and consumes, the tongue of its host fish. The Isopod’s body then functions as the fish’s tongue, allowing the fish to survive. Fish that acquire ectoparasites attempt to remove them by jumping out of the water, rubbing against solid objects, and seeking out “cleaning stations” frequented by Cleaner Shrimp, Cleaner Wrasses, and other fish species that eat the parasites attached to the affected fish. In this symbiotic relationship, the affected fish are cleaned of parasites, do not prey on their cleaners, and the cleaners get a fairly easy meal.