Argas (Microargas) transversus Banks (New Subgenus) (Ixodoidea, Argasidae), a Diminutive Parasite of the Galapagos Giant Tortoise: Redescription of the Holotype Male and Description of the Larva1

Abstract

The single specimen described as Argas transversa, from Albemarle Island in the Galapagos Archipelago, by Ranks in 1902 without reference to host, developmental stage, or sex, proves to be a male measuring only 1.50 mm long. This minute specimen represents one of the smallest tick species known and its transversely oval body bears an exceptional number and variety of lateral and ventral setae, all features that suggest remarkable convergent adaptation of this metastigmatic tick and prostigmatic lizard-parasitizing mites, especially those of the family Pterygosomidae. In addition to a redescription of the long-overlooked holotype male of A. transversus, a larva of this species, from the Round-domed Giant Tortoise, Testudo elephantopus porteri Rothschild, on Indefatigable Island, Galapagos, is here described. The larval stage in many structural respects resembles the adult stage and bears similar though fewer specialized setae. Every criterion of a tick of the genus Argas is satisfied in both developmental stages but owing to the number of unique or unusual features of both the adult and the larva, a new subgenus, Microargas, is proposed to contain A. transversus Banks.