LAUSR

Abstract In the present paper, we review the fossil record of the Hydrometridae (Hemiptera, Gerromorpha) and present a new species from the Early Cretaceous Crato Formation of Northeastern Brazil, Christometra paradoxa gen. et sp. nov. This species is based on a new specimen (a female), as well as a previously figured one (a male), providing a rare case of preservation of sexually dimorphic features in the fossil record. This is the third species coming from this deposit, which is Aptian-Albian in age and the oldest deposit to have yielded hydrometrids so far. Only five other Mesozoic species are known, being slightly younger in age (Cenomanian). So far, phylogenetic analyses have recovered Cretaceous hydrometrids as basal relative to Cenozoic genera but, Christometra paradoxa exhibits several advanced characteristics that unite it in a clade together with the extant genera Hydrometra and Bacillometroides, in a more derived position than any previously known fossil hydrometrid. The present publication is registered in the Official Register of Zoological Nomenclature (Zoobank), under the registration number http://zoobank.org/urn:lsid:zoobank.org:pub:3CFA88AB-3CBC-4CCC-8196-698ECC863947. The registration number for the nomenclatural act of the genus is http://zoobank.org/urn:lsid:zoobank.org:act:84744426-1259-4864-8E3F-E43E0DAB2021, and that of the species is http://zoobank.org/urn:lsid:zoobank.org:act:23700AB2-F7AD-4F50-A5E7-CB28868079B2.