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As stated above, the Drepanidae can be defined by their characteristic
tympanal organs, most recently discussed by Minet (1983), Scoble & Edwards
(1988) and Scoble (1992). They are derived from tergosternal sclerites
connecting sternum A2 with tergum A1, and can be seen as a pair of small oval
structures, each composed of two interconnecting chambers. The tympanum is
uniquely situated within the oval structures between the two chambers. There is
an additional pleural component to each, a fold supported by a three-armed
sclerite, that provides a framework for anterior and posterior counter-tympanal
membranes enclosing the pleural chamber of each tympanal organ. These structures
are described in detail by Scoble, and can be seen in Figs 153 to 155.
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More general features of the group are noted by Scoble & Edwards
(1988), Common (1990) and Scoble (1992). The frenulum, when present, is often
apically clubbed. The forewing venation often shows reduction of branches of the
radial system, usually with a narrow areole within it. The humeral angle of the
hindwing is usually expanded. Vein Sc of the hindwing remains close to Rs, or
approximates to it, just beyond the cell. Chaetosemata are reduced or absent,
and ocelli are usually absent. The male antennae have a tendency to be prismatic
or lamellate (rather flattened), sometimes with pectinations, or more
extensively bipectinate.
The genitalia of both sexes show some variety of structure, the tegumen
usually with socii of some sort. The aedeagus vesica rarely has cornuti. The
bursa copulatrix of the female often has a signum or signa.
Three subfamilies are currently recognised, differing markedly in
appearance and structure. The Australian genus Hypsidia Rothschild,
unplaced to subfamily by Scoble & Edwards (1988), is discussed with the
Thyatirinae. These differences extend to the larvae, where the head is
hypognathous when they are mature. Secondary setae are usually absent or few in
Drepaninae: Drepanini, few in Thyatirinae and numerous in Cyclidiinae and
Drepaninae: Oretini. The anal prolegs are normal in Cyclidiinae, weak in
Thyatirinae and vestigial, without crochets in Drepaninae. The larvae are
arboreal feeding.
The family as a whole is much more diverse in the Old World,
particularly the Oriental Region, to which the Cyclidiinae are restricted.
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