Gomphidae

The Gomphidae is a large cosmopolitan family with high species richness comparable to that of Libellulidae. Gomphids exhibit several apparently ancestral characteristics, such as the widely separated compound eyes and unspecialized wing venation in the adults, 2-segmented fore- and middle tarsi in nymphs and adults, and 4-segmented antennae with antennomere 4 min or vestigial in the nymphs. Nymphs of 27 of the 29 genera of Gomphidae that occur in Thailand are keyed and diagnosed. High-quality photographs of the dorsal and ventral habitus, as well as details of the morphology for all genera, are provided, except the still unknown nymphs of Asahinagomphus and Mattigomphus. Gomphid nymphs are very diverse in shape and size, but are easily distinguishable by the 4-segmented antennae, a movable molar crest on the mandibles, flat prementum, lobe of labial palp lacking long setae, usually abundant coverage of long setae mainly on the legs, and two tarsomeres on the fore- and middle legs. The genera can be identified by the shape of the 3rd antennomere, presence/absence of burrowing hooks, wing sheaths parallel or divergent, presence/absence of dorsal protuberances and posterolateral spines on the abdomen, and abdomen shape. Most of the species inhabit lotic environments, although a few are pond dwellers.