Morphology, evolution and a classification of the Gerridae (Hemiptera-Heteroptera)

Abstract

This work is a study of the morphology, evolution and classification of the Gerridae of the World. Fifty genera and sixteen subgenera out of fifty-three genera and sixteen subgenera known were examined. In the section on morphology it is attempted to establish homologies and a tenninology for as many external structures as possible. In the section on the structural evolution the process of evolutionary change of each structure is traced, and its taxonomic significance is discussed. The postembryonic development of the antennal and leg segments has been studied in representative species of each major group to see how the different proportional lengths of antennal and leg segments are realized ontogenetically; how the ontogenetic growth patterns for these segments have been carried over to adult phylogeny; and how the growth patterns themselves have evolved. It was found that ( I ) the antennal and leg segments show roughly a simple allometric growth, with either an appreciable increase or decrease in growth ratio at the final stage of development; (2) often lengths of the leg and antennal segments of adults in a great majority of species within a genus fall roughly on the growth lines for the corresponding segments in a representative species of the same genus, indicating that species within a genus share very similar growth patterns for corresponding segments; (3) a hypothetically primitive growth ratio for the antennal segments (k = 1.142) is suggested; (4) a process of development of the proximo-distal gradient in growth ratios for the antennal segments in the phylogeny of the Gerridae is traced; ( 5 ) for certain segments, such as the hind tibia, there is evidence in many genera that the growth patterns vary among species of a genus, thus forming the secondary phylogenetic allomorphic lines; ( 6 ) as a result of the formation of the secondary allomorphic slope for the hind tibia, which is always steeper than that for the hind femur, the tibia is shorter in relation to the femur in the smaller species of a given genus, and this tendency occurs in most major groups of the Gerridae; (7) since there is a striking tendency toward smaller body size in the structurally more specialized forms at all taxonomic levels, and the congeneric species often appear to have very similar allometric growth patterns for corresponding antennal and leg segments, the lengths of antennal and leg segments in the early postembryonic developmental stages in larger and primitive species roughly approximate the lengths of the same in adults of related but phylogenetically more advanced forms. In the light of the knowledge gained from the study of evolution of the leg and antennal segments, the taxonomic status of all groups of the Gerridae (subfamilies, tribes, genera and subgenera) is evaluated. The arrangement of genera in the proposed new classification of the Gerridae follows. Trepobatinae is described as a new subfamily and Hermatobatinae is excluded from the Gerridae. ( 1 ) Gerrinae. Gerrini, including Gerris (Gerris s. str., Aquarius, Limnoporus), Gerriselloides, Gerrisella, Gigantometra, Tenagogerris, Eurygerris, Lirnnogonus (Limnogontis s. str., Limnogonellus), Tachygerris, Tenagogonus (Tenagogonus s. str., Lunnometra, Tenagometra), Tenagometrella. Cylindrostethini, including Cylindrostethus, Potamobates, Flatygerris. Charmatonietrini, including Charmatometra, Brachymctra, Eohates. Eotrechini, including Eotrechus, Onychotrechus, Chimarrhometra, Amemboa, Rheumatotrechusi?). (2) Ptilomerinae, including Ptilomera (Ptilomera s. str., Proptilomera), Potamometra, Rhyacobates, Heterobates, Potamometroides, Potamometropsis, Rheumatogonus, Pleciobates. ( 3 ) Halobatinae. Halobatini, including Asclepios, Halobates. Metrocorini, including Metrocaris, Eurymetra, Eurymetropsiella, Eurymetropsielloides, Eurymetraj)sis, Ventidius (Ventidius s. str., Ventidioides), Esakia. (4) Rhagadotarsinae, including Rimgadotarsus (Rhagadotarsus s. str., Caprivia), Rheumatobates (Rheumatobates s. str., Hynesia). (5) Trepobatinae, including Trepobates, Tehnatometra, Trepobatoides, Halobatopsis, Ovatametra, Rheumatometroides, Stenobates, Cryptobates, Naboandelus, Htjnesionella, Metrobates, Rheumatornetra, Metrobatopsis.