Echo, Selys, 1853

Orr, Albert G. W., 2024, A review of present knowledge of larvae of the Calopterygoidea (Zygoptera) of the Oriental realm, including keys to families and known genera, Zootaxa 5497 (2), pp. 209-243 : 224

Echo

The genus includes five species ranging from southern China and the eastern Himalayas to the Malay Peninsula and Sumatra. Only the larva of Echo uniformis Selys from Sumatra has been briefly described and illustrated ( Lieftinck 1965, van Tol 1992), with drawings showing the habitus and the prementum with labial palps. Nevertheless, both illustrations and the brief text convey critical information that separates the genus from any other, including its sister genus Psolodesmus (according to Dumont et al. 2007), which is confined to Taiwan and southern Japanese Islands. The prementum ( Fig. 33 ) is very similar to that of Psolodesmus , but has two setae on the anterior lobes of the prementum (one in Psolodesmus ). Both genera have a similar robust build ( Fig. 56 ). Also in Psolodesmus the short outer, triquetral caudal gills bear very strong teeth along the outer central ridge but not on the dorsal and ventral margins, whereas in E. uniformis all three ridges bear dentition, according to Lieftinck’s (1965) text, and illustration. The larva of E. modesta Laidlaw has been collected on Langkawi Island, Malaysia (S.G. Butler pers. comm.), and, an F- 1 specimen was collected by AGO in a leaf pack in a very small and shallow rocky branch of a small forest stream in Kanchanaburi, Thailand in 2003. Adult E. modesta were present and no other species with which the larva might be confused occurs in the area. The species has also been bred, but not yet described (T.S. Keetapithchayakul pers. comm.), confirming the above identifications. Both specimens have strong dentition dorsally and laterally on the margins of the caudal gills as well as lighter denticulations on the outer central ridge ( Fig. 43 ); the central gill, which is almost as long as the lateral ones, has dorsally at its base a broad triangular sclerotised and slightly serrate guard plate for about one third its length, which is also well developed on E. uniformis . The other genus in which the prementum is similar is Mnais , but as in Psolodesmus it differs in bearing only one pair of setae on the lobes of the prementum. In addition the known larvae of Mnais are less heavily built and the margins of the outer caudal gills are smooth, without dentition, and usually longer and narrower.

Nevertheless, in southern China there is a distinct possibility that species of Echo and Mnais may overlap ( Zhang 2019), and it is unclear if any of those Echo species ( E. candens Zhang et al. , E. margarita Selys and E. perornata Yu & Hämäläinen ) have the same larval form and same distinguishing characters as E. uniformis and E. modesta , or indeed, if all Mnais species differ in the way we presently recognise. A possible hint as to the differences we may expect has been suggested ( Orr & Butler 2024), but until we have certified voucher specimens, this question remains open.

Figures

FIGURES 27–34. 27. Prementum of Calopterygidae showing measurements used in family key (based on Calopteryx japonica, redrawn from Miyakawa 1983). 28. Neurobasis chinensis, prementum and left labial palp (redrawn from Lieftinck 1965). 29. Matronoides cyaneipennis, prementum and labial palps (ventral view). 30. Matrona basilaris, prementum (dorsal view, drawn from Wang et al. 2017). 31. Atrocalopteryx atrata, prementum (dorsal view, redrawn from Miyakawa 1983). 32. Mnais tenuis, prementum (dorsal view, redrawn from Matsuki & Lien 1977). 33. Echo uniformis, prementum and left labial palp dorsal view (redrawn from Lieftinck 1965). 34. Psolodesmus mandarinus, prementum (dorsal view, redrawn from Matsuki & Lien 1978).

FIGURES 52–56. 52. Caliphaea angka, habitus (based on Yang et al. 2021). 53. Vestalis gracilis, habitus (redrawn from Rattanachan et al. 2022). 54. Neurobasis chinensis, habitus (original drawing). 55. Matrona basilaris, habitus (drawn from Wang et al. 2017). 56. Echo uniformis, habitus (redrawn from Lieftinck 1965).

FIGURES 42–51. 42. Archineura incarnata: caudal gills; left lateral above, median below (drawn from Yang et al. 2022). 43. Echo modesta: caudal gills; left lateral above, median below, with baso-dorsal shield arrowed (original illustration). 44. Psolodesmus mandarinus, dorsal view of caudal gills, with baso-dorsal shield of median gill arrowed (redrawn from Matsuki & Lien 1978). 45. Mnais andersoni, left lateral caudal gill with upper margin of median gill visible; baso-dorsal shield of median gill arrowed (original illustration). 46. Mnais gregoryi: caudal gills; left lateral above, median below, with baso-dorsal shield arrowed (drawn from Yang et al. 2021). 47. Caliphaea angka: caudal gills; left lateral above, median below (drawn from Yang et al. 2021). 48. Matrona basilaris: caudal gills; left lateral above, median below (drawn from Wang et al. 2017). 49. Vestalaria venusta: caudal gills; left lateral above, median below (drawn from Wang et al. 2017). 50. Vestalis amoena group: caudal gills; left lateral above, median below (redrawn from Lieftinck 1965). 51. Vestalis melania: caudal gills; left lateral above, median below (redrawn from Guadalquiver et al. 2022).