Taxonomy: Animalia, Arthropoda, Crustacea, Maxillopoda, Copepoda, Siphonostomatoida, Pennellidae, Lernaeocera, L. branchialis
Description & Lifestyle: L. branchiallis begins life as a naupilus (curstacean larvae), which then molts and becomes a copepodid, which is a 0.5mm long, free swiming larval stage (shown on the right). The copepod then has 24 hours to locate an intermediate host, which is usually a benthic fish species. They use hook-like appendages to attach themselves to the gills of a fish, where they feed on the blood of the fish with a filamentous structure and males pass sperm to the females. After four more molts, L. branchialis now enters the chalimus stage, gaining setae and becoming free swimming. The female (2-3mm long) then searches for a fish of the family Gadidae (its primary host), which it enters the gill slits of and attaches itself to. Here, the female enters its final life stage, becoming a sac-like organism with a characteristic string of eggs at its posterior. At the anterior end, the organism branches itself into an antler-like structure, connected to the main artery of the fish. In this way, it takes in blood from one end and releases eggs from the other.