Echinophthirius horridus

Echinophthirius horridus is found in northern holarctic regions (Durden and Musser, 1994), i.e., in temperate, subarctic, and arctic coastal areas of the north Atlantic and Pacific Oceans, where its seal hosts may also be found (Grzimek, 1990). (Durden and Musser, 1994; Grzimek, 1990)

The immediate habitat of E. horridus may be described as the skin of its only known host, the true seal (Phoca vitulina). The more indirect habitat of this parasite is the habitat in which its seal hosts live. True seals, also known as harbor seals, bask and sleep on both rocky coastal ledges and sandy beaches which are uncovered at low tide. These seals stay near the shore in order to feed in the shallow coastal waters. (Grzimek, 1990)

Anoplurans, or sucking lice, resemble their chewing relatives in that they have small, wingless, flattened bodies. However, while chewing lice (order Mallophaga) retain mandibles for biting into their hosts, these structures are completely absent in Anopluran lice. Instead, Anoplurans have mouthparts that are highly modified for sucking the blood of their hosts. These mouthparts include four elongate stylets that form a fascicle, which pierces through the host's skin, withdraws blood, and conveys salivary material into the wound (Roberts and Janovy, 2000).

Anoplurans of the genus Echinophthirius have large fore-, mid-, and hindlegs, each equipped with a blunt claw that is used to grasp tightly to the skin and fur of their Pinniped hosts as they move about on land or in water (Kim et al., 1986). The head and thorax of these lice are thickly covered in hairs called setae and no eyes are present externally (Miller, 1971). Their abdomen is leathery with six pairs of small respiratory spiracles (Price and Graham, 1997). (Kim, Pratt, and Stojanovich, 1986; Miller, 1971; Price, Graham, and July, 1997; Roberts and Janovy, 2000)

Like all Anopluran lice, the developmental stages of E. horridus include an egg, three nymphal instars, and an adult stage (Roberts and Janovy, 2000). The hatching of an egg is followed by a slow metamorphosis, during which the nymph becomes slightly more similar to an adult with each of the three moltings of its exoskeleton. This mode of development is termed hemimetabolous. (Roberts and Janovy, 2000)

The lifespan of E. horridus is not known.

In the family Echinophthiriidae, to which E. horridus belongs, some of the body setae have become highly modified into flattened, overlapping scales (Grzimek, 1975). In some species, these setae help to trap an air bubble, or plastron, around the body of the louse through which the louse respirates (Marshall, 1981). However, E. horridus is not capable of this form of respiration. In the water, E. horridus stretches out its legs and cannot move (Messner, 1998).

The tendency for seals to form groups at traditional "haul-out" sites facilitates the transmission of E. horridus (Thompson, 1998). Studies of just how these lice spread have suggested contradictory methods. One study indicated that E. horridus was transmitted vertically from mother to pup while nursing, while another study suggested horizontal transmission (Thompson, 1998). It is evident in either case, however, that physical contact between seals while on land is necessary for the dispersal of E. horridus. (Grzimek, 1975; Marshall, 1981; Messner and July, 1998; Thompson, 1998)

Anopluran lice have short antennae bearing chemoreceptors and tactile hairs. They are also thought to have the ability to detect chemicals in the host's bloodstream that let them know when they have hit a blood vessel.

No information is available on how these lice communicate with one another. (Roberts and Janovy, 2000)

Echinophthirius horridus feeds exclusively on the blood of true seals (Phoca vitulina) during all stages of development (Geraci et al., 1981). Echinophthirius horridus uses the blunt claws on the ends of its legs to grasp tightly onto the seal while feeding. The louse uses its sucking fascicle to pierce through the skin of the seal directly into a blood vessel from which it withdraws blood. This mode of feeding by the direct insertion of mouthparts into a blood vessel is termed solenophagy (Greek for pipe + eating). A two-chambered pump located within the louse's head acts as a suction, while salivary anticoagulants keep the blood flowing smoothly (Roberts and Janovy, 2000). (Geraci, St. Aubin, and Hicks, 1981; Roberts and Janovy, 2000)

Echinophthirius horridus is an obligate ectoparasite of true seals. There are two important ways in which E. horridus affects its seal hosts. First, high burdens of these ectoparasites may compromise the seal's diving ability and thus its ability to successfully capture prey (Thompson, 1998). This can become even more serious if a nursing mother seal cannot catch enough food to ensure a healthy milk supply for her pup. In addition, E. horridus has been found to be an intermediate host of the seal heartworm, Dipetalonema spirocauda, which can be fatal (Geraci, 1981; Lunneryd, 1992). It is not known if either of these effects of E. horridus on its host are serious enough to cause a significant decrease in seal populations, but the threat is present. (Geraci, St. Aubin, and Hicks, 1981; Lunneryd, 1992; Thompson, 1998)

This parasite has no known impact on humans.