Phylogenetic analysis of Hydrometridae Billberg, 1820 (Insecta: Hemiptera: Heteroptera)
Semiaquatics bugs, Phylogeny, Gerromorpha, Neotropical
Hemiptera is a monophyletic group of insects whose main synapomorphy is the
modification of the mandibule and maxilla into concentric piercing-sucking stylets, with
the labial and maxillary palps being absent. The order gathers four suborders, among
which only Heteroptera has aquatic representatives. Heteroptera is monophyletic and
has three main synapomorphies: the scent gland apparatus of the metathorax in adults,
the dorsal abdominal scent gland apparatus in nymphs, and a strong reduction of the
tentorium (internal chitinous scaffold of the head). Representatives of the infraorder
Gerromorpha are known as semiaquatic heteropterans, or true bugs, and occupy a wide
range of environments, such as humid terrestrial habitats, not necessarily close to water
bodies, phytotelmata, habitats marginal to freshwater bodies or their surface, coastal
marine habitats, and even the open ocean. Among the families of Gerromorpha,
Hydrometridae currently includes three subfamilies (Hydrometrinae, Heterocleptinae e
Limnobatodinae), with ten extant genera and about 130 species distributed worldwide,
except for Antarctica, and 11 fossil genera, the oldest of which is dated from the Lower
Cretaceous. For the present study, a phylogenetic analysis of Hydrometridae was
performed based on morphological characters. The outgroup was formed by four
families of Gerromorpha considered closely related to Hydrometridae in previous
studies, while the ingroup gathered eight of the ten recent genera of the family, in
addition to two undescribed genera from islands of the Pacific. At total, 110 characters
(68 binary and 42 multistate) were described and coded, several of which were
illustrated in order to facilitate their interpretation. The phylogenetic analysis was
performed through heuristic searches with equal weights using TNT 1.5 no taxon limit
and by Bayesian Inference using MrBayes 3.2.2. The monophyletism of Hydrometridae
was not recovered, because Veliometra Andersen, 1977 (Heterocleptinae) was
recovered as sister-group to Macrovelia hornii Uhler, 1872 (Macroveliidae).
Hermatobatidae was recovered as the sister-group of Hydrometridae. Hydrometrinae
was not recovered as monophyletic due to the position of Limnobatodinae as the sister-
group of (Bacillometra Esaki, 1927 + Hydrometra Latreille, 1797), being closer to them
than other genera integrating the former subfamily. The subfamily Heterocleptinae,
including two recent and two fossil genera, is transferred to Macroveliidae. The
remaining three recent and one fossil genera attributed to Macroveliidae are allocated in
Macroveliinae. Two new subfamilies are erected to include genera previously allocated
in Hydrometrinae, Cephalometrinae (type-genus: Cephalometra Polhemus & Ferreira,
2018) and Chaetometrinae (type-genus: Chaetometra Hungerford, 1950). Considering
the recent genera, Hydrometrinae now includes only Bacillometra, Hydrometra, and
Bacillometroides Polhemus & Polhemus, 2010. The fossil genera that remain attributed
to Hydrometridae are all allocated in Hydrometrinae, some provisionally until they are
evaluated in a phylogenetic context.