Lepidophthirus macrorhini is a species of seal lice (Echinophthiriidae), the type species of its genus Lepidophthirus. The primary hosts of these lice are the southern elephant seal, with the lice infesting their pelage; this seal species is one of the deepest diving mammals, surpassing all but two species of whales in their foraging dives. Thus, the lice infesting their hides needed to adapt alongside their hosts, and L. macrorhini is capable of enduring extreme hydrostatic pressures that they experience as the seal dives into the bathyal zone, over 2,000 metres (6,600 ft) below the ocean's surface. Despite the adults' resistance to pressure, the nymphs and especially the eggs must remain on dry land to survive, so the elephant seal lice reproduces during times when the elephant seals haul out for extended periods, such as during their breeding season.
Description In its 1904 initial description on the basis of 2 male and 21 female specimens recovered by one Dr. Werth, Enderlein compared the newly discovered louse to Echinophthirius lice which parasitize various seals such as Phoca spp. and Phocarctos hookeri. Despite their overall morphological similarity, the "scales" of this species is distinct from the spines of Echinophthirius; this difference lead him to establish the genus Lepidophthirus, with L. macrorhini (after a historical scientific name for southern elephant seals; Macrorhinus leoninus) being the type species by monotypy. A second species, L. piriformis, would later be described in 1966. The head of this species is wider above, with the mouth positioned at the front of its underside. The species has no eyes, and its antennae have four segments. Its legs are robust, being short and squat. Lepidophthirus' scales densely occupy the top surface of the body, and there are no spines underneath this scale layer. Coloration tends to be brown with the sclerotized claws being darkest. There are two dark brown spots on top of the thorax surrounded by lighter regions; a pale and narrow longitudinal line runs between these regions. Compared to other species in the family, L. macrorhini has a more rounded posterior region, a posterior projection of the coxae, an expanded rostrum, and a more robust first leg pair with a "well-developed" nail- or hook-like tarsal claw; in general, this species is larger and rounder-bodied than other Echinophtiriids. The respiratory system of the louse consists of a well-developed tracheal tree with two main trunks which connect together within the abdomen's posterior. The spiracles, which are the respiratory system's orifices, protrude from the body wall which is unlike the flat or flush spiracles on human lice. The spiracles of seal lice have a closure system made up of heavily sclerotized cuticular plugs and cuticular rods along with their associated muscles; the rod acts as a piston which closes the spiracle when necessary. This mechanism is more elaborate and complex than other Anopluran lice. The tracheal and digestive systems, which are inherently hollow, are thought to collapse when exposed to high water pressure during dives.
Distribution As in other lice, L. macrorhini is an obligate ectoparasite; the types were recovered from a young male southern elephant seal which lived on the Kerguelen Islands, with subsequent studies confirming no other regular hosts (though one record exists of a Weddell seal infested by L. macrorhini), and that they infest elephant seals in the King George, Macquarie, and Elephant Islands as well. Genetic analysis comparing this species to other Echinopthiriid lice shows that they have comparatively higher population mutation rates, indicating a higher overall population size and heterozygosity; of the Echinopthirid host species studied, southern elephant seals have the greatest geographical distribution.
Biology
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