Marquesametra D. Polhemus 2022, n. gen.
Creators: name: Polhemus, Dan A.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hemiptera
Hydrometridae
Marquesametra

description: Marquesametra D. Polhemus, n. gen.
Figs. 1–8, 38
Description. Body small for family, narrow (Fig. 1); length less than 5.0 mm.
Color: Ground color brown with abdominal mediotergites lighter; pruinose markings present on dorsal and lateral thorax, and on each laterotergite; ventral surface darker; legs and antennae brown.
Structural characters: Head relatively long, 0.55 times the length of the thorax and abdomen combined; anteocular portion slightly shorter than postocular portion, ratio 1.0/1.3; eyes small, width of an eye as viewed from above less than width of interocular space; labium long, reaching onto prosternum between anterior margins of fore acetabula; antennae long, about 0.60 times total body length, slender, antennomere II only slightly longer than antennomere I, antennomere III slightly over 3 times as long as antennomere II, antennomere IV almost exactly 3 times as long as II, antennomere I stouter than antennomeres II–IV, antennomere IV slightly inflated apically; posterior pair of cephalic trichobothria set on low tubercles, length exceeding the distance between these tubercles and anterior margin of pronotum.
Thorax widened posteriorly; pronotal lobe short, extending posteriorly over mesonotum, metanotum exposed, without any trace of wing pads.
Legs slender, but not threadlike, total length of hind leg equal to length of body; fore-to-middle versus middleto-hind coxal spacing subequal, ratio 1.00/1.20; pretarsus with both dorsal and ventral arcuate arolia, parempodia long, setae-like.
Abdomen with mediotergites II–VII quadrate, equilateral or nearly so; male abdominal sternum VII unmodified, lacking paired sclerotized processes or patches of bristle-like setae.
Type-species. Marquesametra hivaoa n. sp.
Etymology. The generic name Marquesametra is derived from the island group, the Marquesas, to which it is endemic, and metra, measurer. Gender feminine.
Distribution. Marquesas Islands, Hiva Oa.
Discussion. Marquesametra is a wingless, terrestrial hydrometrid occurring in the upland cloud forests of Hiva Oa island, in the Marquesas group. Although at first glance when seen in the field it resembles a minute Hydrometra, it clearly stands apart from that genus by its much shorter head capsule, with the anteocular portion of the head being shorter than the postocular portion (1.00/1.15), versus the character state in Hydrometra where the anteocular head is 2–3 times longer than the postocular portion (see J. Polhemus & D. Polhemus 1995c, Fig. 2). In addition, the abdomen is proportionally shorter and broader, with the abdominal mediotergites of Marquesametra being square and equilateral, versus the character state seen in Hydrometra, where these tergites take the form of elongate rectangles with their lengths being over 4 times their widths (see J. Polhemus & D. Polhemus 1995c, Fig. 4). The spacing between the fore-versus-middle and middle-versus-hind coxae in Marquesamatra is nearly subequal, being 1.0/1.2, whereas in Hydrometra the hind coxae are far more posteriorly displaced, with this ratio usually on the order of 1.0/2.0. Finally, the legs of Marquesametra are also relatively shorter and stouter in relation to the body, with the total length of the hind leg being merely equal to the length of the body, versus clearly exceeding the body length in Hydrometra.
This genus shows certain similarities to the subsequently described Prohydrometra from the Society Islands, but in that genus the fore-middle versus middle-hind coxal spacing ratio is slightly more unequal, being greater than 1.4 (compare Figs. 3, 9, 13). The abdomen in Prohydrometra is also slightly more elongate, with the abdominal mediotergites being slightly rectangular, and longer than wide. The male abdominal sternum VII in Prohydrometra also exhibits consistent modifications in the form of paired processes or setal patches, which are absent in Marquesametra and the other two endemic Marquesan genera. Finally, in all species of Prohydrometra, antennomere III is extremely prolonged, being 5 times the length of antennomere II (Fig. 11), versus only about 3 times as long in Marquesametra (Fig. 1). The two genera also inhabit different volcanic archipelagoes separated by an ancient water gap of over 1400 km, and as such are markedly allopatric.
In comparison to the other two endemic genera of Hydrometridae found in the Marquesas, Dolichocephalometra and Chaetometra, the differing form of the head capsules will easily separate these two taxa from Marquesametra (compare Figs. 1, 32, 37). In Dolichocephalometra the head is very elongate, being nearly as long as the body and having the eyes highly reduced, while the head capsule in Chaetometra is much shorter and bears long, erect pilosity that also occurs on the remainder of the body and the legs.
All of the genera discussed above do share certain common character states, including: 1) the posterior pair of cephalic trichobothria set on low tubercles; 2) pretarsus with both dorsal and ventral arcuate arolia, and long, setae-like parempodia, 3) an absence of modifications to male abdominal sternum VII; and 4) a simple cuticular microstructure consisting of short, slightly curling setae covering the body, with interspersed longer, dark, bristlelike setae, but with an absence of dark denticles or plates. These character states are all considered plesiomorphic within Hydrometridae as a whole (Andersen 1982a).
description: Published as part of Polhemus, Dan A., 2022, Two new genera and six new species of Terrestrial Hydrometridae (Hemiptera: Heteroptera) from French Polynesia, pp. 69-98 in Zootaxa 5190 (1) on pages 71-72, DOI: 10.11646/zootaxa.5190.1.3, http://zenodo.org/record/7119849