Amemboides Polhemus & Andersen, 1984

Tran, A. D. & Polhemus, J. T., 2009, Two new species of the genus Amemboides Polhemus & Andersen, 1984, stat. nov. (Hemiptera: Heteroptera: Gerromorpha: Gerridae) from Vietnam, Zootaxa 2216, pp. 49-56 : 50-51

Genus Amemboides Polhemus & Andersen, 1984 , stat. nov.

Amemboa (Amemboides) Polhemus & Andersen, 1984: 99–100 (type species Amemboa (Amemboides) perlata Polhemus & Andersen, 1984 , by original designation).

Diagnosis. Size: males, length 3.3–4.9 (apterous), 4.3–6.1 (macropterous); females, length 4.0–5.6 (apterous), 5.0–6.4 (macropterous). Dorsum pale, dark markings indistinct. Antennae subequal to body length, segments 1 and 2 subequal in length, segment 3 distinctly longer than first 2 segments, segment 4 longest; segment 1 with around 3–5 short spines at distal part only. Rostrum reaching anterior ¼ of mesosternum, labial segments 1 and 2 combined much longer than segment 4. Pronotal lobe completely reduced in apterous form, wellproduced in macropterous with rounded hind margin. Relative lengths of mesosternum and metasternum around 4.6–6.0 times. Scent orifice small, situated on posterior part of metasternum, on well-elevated area. Front femur simple, only basally incrassate in males, ventral sometimes with short black hairs in males, not modified in females. Tarsal segment 1 of middle leg distinctly less than twice the length of segment 2; tarsal segment 1 of hind leg shorter than segment 2. Male abdominal venter not depressed; sternum 7 slightly longer than 2 preceding sterna combined, with hind margin emarginated. Male genitalia: pygophore simple, usually with rounded hind margin or sometimes emarginated; proctiger without lateral arms; paramere distinct, usually long, and diagnostic; endosoma with apical sclerites fused with dorsal sclerites, long lateral sclerites, ventral sclerites membranous. Female abdominal venter about ⅓ of body length, but variable as most species with two forms, either pregenital segments well extended or posterior segments folded into preceding segments; sternum 7 shorter than all preceding sterna together, connexival angles sometimes well-produced. Female genital segments usually withdrawn into pregenital abdomen. (Modified from Polhemus & Andersen, 1984; Chen et al., 2005).

Remarks. Polhemus & Andersen (1984), when describing Amemboides , treated it as a subgenus of Amemboa based on their cladistic analysis (see Polhemus & Andersen, 1984: 66–68, 74) in which Amemboa and Amemboides formed a monophyletic group. Another reason was the existence of A. philippiensis , which possesses some diagnostic features of both Amemboa (s.str.) and Amemboa (Amemboides) . However, after recent examination of the holotype of this species, we believe that this species may even belong to a separate genus (see below). Additionally, at that time, because there were only few species of Amemboa (Amemboides), Polhemus & Andersen (1984) had doubts about the diagnostic features of two subgenera, and thus they had reservations about establishing a new genus. Since 1984, more species of both Amemboa (s.str.) and Amemboa (Amemboides) have been discovered; and these discoveries show clear distinction between the two subgenera. Therefore, the relationship between Amemboa (s.str.) and Amemboa (Amemboides) needs to be re-elucidated.

With regard to the taxonomic position of Amemboa philippiensis: This species was originally treated under the nominate subgenus Amemboa . Re-examination of the female holotype (which is not complete, with some leg segments missing, labelled “Nord Mindanao, Tankulan 1000f, leg. G. Böttcher, 19.6.15” deposited in BMNH) shows that it is a good species, although the male specimen is not known. For the middle legs, only the left remained, but the tip of the tarsus (from the insertion of claws) was broken; the full length of tarsal segment 2 here is estimated at 0.29 (at least 0.27), while that of tarsal segment 1 is 0.51. Thus, in the middle leg, tarsal segment 1 is less than twice as long as segment 2. This, however, does not fit with the diagnosis of the genus Amemboa (s. str.) Esaki, 1925 (sensu Polhemus & Andersen, 1984). Also, the “tuberculate omphalium” is absent in all known Amemboa species , but is instead diagnostic for Amemboides . However, other characteristics, such as labial segments 1 and 2 combined much shorter than segment 4, antennal segment 1 with spines scattered along its length, dorsal colour pattern, are diagnostic for Amemboa . The structures of female gonapophyses are of intermediate form between those of Amemboa and those of Amemboides . These conflicting data sets make it difficult to ascertain if “ Amemboa philippiensis ” belongs to Amemboa or Amemboides . We now believe it actually belongs to an undescribed genus. In our present study, we did not have an opportunity to go to the type locality to collect fresh specimens. Until the male specimens are found (ideally, from the type locality), the position of this species in the Eotrechinae remains uncertain.

In the cladistic analysis by Polhemus & Andersen (1984), Amemboa and Amemboides were grouped together with Onychotrechus and Tarsotrechus on the basis of the relative lengths of the mesosternum and metasternum (length of mesosternum greater than 4.0 times the length of metasternum). However, recent observations have shown that these ratios overlap in different genera: in Eotrechus varying between 1.7–5.3 times, in Chimarrhometra 3.3 times, in Onychotrechus and Tarsotrechus varying between 6.0–7.0 times. After examining many species of Amemboa (s. str.) and Amemboa (Amemboides) , we find that the ratios of each group are actually very discrete. That for Amemboa species is around 7.0–10.0 times, whereas in Amemboides species , it is around 4.6–6.0 times.

Although species of Amemboa s. str. and Amemboides share several similarities [e.g., overall body shape, relative lengths of antennal segments (segment 4 longest), length of rostrum (reaching anterior ¼ of mesosternum)], these two groups can also be easily separated by the following: colouration of their body (dorsum of Amemboides pale, without distinct dark markings as in Amemboa ), relative lengths of tarsal segment 1 to tarsal segment 2 of middle leg (distinctly less than 2.0 times in Amemboides ; about 2.0 times in Amemboa ), modification of male front femur (simple, unmodified in Amemboides ; strongly modified in Amemboa ), and especially the modification of genital segments (in Amemboides : pygophore and proctiger simple, paramere well-developed; in Amemboa : pygophore and proctiger strongly modified, paramere very small). In our opinion, these differences are very significant and Amemboides requires generic ranking. A separate study using molecular datasets also supports the hypothesis that Amemboa s. str. and Amemboides form a paraphyletic group (Tran, Meier & Ng, in prep.) and that the latter is a valid genus. The results for this will be published separately as this involves a more complete molecular phylogenetic study of the subfamily Eotrechinae . In this paper, Amemboides Polhemus & Andersen 1984 , is recognised as a separate genus.

Species of Amemboa and Amemboides , although living on the water surface, tend to stay very near the water’s edge and often rest on the banks. While the genus Amemboa has the widest distribution that corresponds to Eotrechinae’s range, Amemboides is restricted to South Asia and continental Southeast Asia ( Polhemus & Andersen 1984; Chen et al. 2005). To date, the genus Amemboides Polhemus & Andersen, 1984 , stat. nov., contains 11 species (and one subspecies) ( Polhemus & Andersen 1984; Zettel 1995; Zettel & Chen 1997; Zettel et al. 2007). Two more species are described in this paper: Amemboides falcatus and Amemboides gladiolus , both from Vietnam. This paper also reports the occurrence of Amemboides sexualis ( Polhemus & Andersen, 1984) from Vietnam for the first time. These findings have increased the number of Amemboides species reported from Vietnam to seven.

As a result of the recognition of the genus Amemboides , the following species-group names are also new combinations:

Amemboides nodosus ( Polhemus & Andersen, 1984) , comb. nov.

Amemboides perlatus ( Polhemus & Andersen, 1984) , comb. nov. (*)

Amemboides pilifer ( Zettel, Yang & Tran, 2007) , comb. nov.

Amemboides ptychoconnexiva ( Polhemus & Andersen, 1984) , comb. nov. (*)

Amemboides setosus ( Polhemus & Andersen, 1984) , comb. nov.

Amemboides sexualis ( Polhemus & Andersen, 1984) , comb. nov. (!)

Amemboides vasarhelyii ( Zettel, 1995) , comb. nov. (*)

Amemboides velaris velaris ( Polhemus & Andersen, 1984) , comb. nov.

Amemboides velaris orientalis ( Zettel & Chen, 1997) , comb. nov. (*)

Amemboides yunnanus ( Zettel, Yang & Tran, 2007) , comb. nov.

Asterisk (*) marks refer to species recorded from Vietnam; (!) mark refers to the first record for Vietnam.