Cyamidae – Whale lice

Cyamids, commonly known as whale lice, are a family of crustaceans (Cyamidae) belonging to Amphipoda Latreille, 1816. They are considered ectoparasites as they feed on cetacean skin, although it remains unclear whether they eat dead or attached skin (or both).

Adapted to life in the highly dynamic marine environment, whale lice have a flattened body, robust ventral spines, a pair of antennae, and specialized mouthparts. They spend their entire life on cetaceans, attached to external surfaces with reduced water flow (including natural orifices such as the blowhole or the genital slit, or near other epibionts like barnacles).

These crustaceans display a remarkable variety of shapes and sizes — ranging from just 3 mm in species like Syncyamus aequus (Lincoln & Hurley, 1981), typically found on small odontocetes like the striped dolphin, to up to 30 mm in species such as Cyamus boopis (Lütken, 1870), which is commonly associated with the humpback whale (Megaptera novaeangliae). Despite this diversity, they share several characteristics typical of amphipods. Their pereion (midsection) consists of five pereionites, each bearing a pair of hook-like appendages called pereopods that they anchor to their host’s skin. The first pair, the gnathopods, is larger and differs between males and females. These are crucial both for gripping the host and mating, as males use them to clasp females during copulation. Interestingly, female cyamids possess a specialized brood pouch or marsupium, where eggs are safely retained until they hatch.

Cyamids lack swimming stages and are thus transmitted by contact between their cetacean hosts. This life trait makes them suitable candidates for investigating cetacean intra- and interspecific interactions, and there are several examples of this indicator use. For instance, cyamid species composition has been used to detect sex and age segregation in sperm whale, while the genetic structure of whale lice has allowed the investigation of whale population structure and species divergence. Also, the presence of C. boopis on a southern right whale, Eubalaena australis (Desmoulins, 1822), indicated interspecific interaction with its typical host, the humpback whale, years before it was confirmed by a photographic record by photographer Jess Wohling.