New larval records of the extinct hard tick Compluriscutula vetulum (Arachnida: Ixodida) from Burmese amber, with notes on its morphology

Abstract

The hard tick Compluriscutula vetulum Poinar and Buckley, 2008 (Ixodida: Ixodidae) from the mid-Cretaceous (ca. 100 Ma) Burmese amber of Myanmar was first described in a new, extinct genus based on a larva. Here, several more larvae are documented providing additional morphological data based on optical studies using a Keyence VHX-6000 Digital Microscope supplemented by computed microtomography (µ-CT). We confirm the presence of 14 festoons (not 13) on the posterior margin of the body, a character unique for the genus. We further describe an unusual pattern of hypostome dentition in the mouthparts, with an unequal and uneven 2/2 arrangement. Moreover, on the internal side of the palps, to the second and third segments five tooth-like elements are present, similar to the hypostome dentition. Fossil ticks are generally very rare, thus the discovery of numerous new specimens of C. vetulum suggests that it may have been relatively common in the Burmese amber forest. Larval instars predominate in the fossil record and we might speculate that they preferred arboricolous hosts.