Mnais, 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 : 225-226

Mnais

Within the Oriental realm there are nine described species in the genus Mnais but this number is likely to increase as suggested by Zhang (2019). The genus ranges from China and Japan to Indochina, Thailand and Myanmar. Two species, Mnais costalis Selys and M. pruinosa Selys are known only from the main islands of Japan and fall outside the Oriental region, but their larval morphology, figured in detail by Hirose & Rokuyama (1966), Ishida (1996), and revisited by Hayashi et al. (2004), are considered here as they give insight into the range of variation within the genus. The larva of M. tenuis Oguma was described from Taiwan (as M. andersoni tenuis ) by Matsuki & Lien (1978). The larva of M. mneme Ris was described and figured by Matsuki & Saito (2000) and photographs of a young larva and some details of a more mature specimen of the same species are provided by ( Ng 2024b). The larva of M. andersoni is known (Orr & Keetapithchayakul unpublished data), with the caudal gills figured ( Fig. 45 ). The larva of M. gregoryi Fraser was described in detail by Yang et al. (2021) from specimens collected at ca 2300 m in Yunnan, China.

In all species the head is fairly broad and semi-pentangular; the body moderately stout to elongate ( M. gregoryi ). Hirose & Rokuyama’s (1966) and Ishida’s (1996) illustrations of the habitus show stouter bodies in M. costalis and M. pruinosa , and this is confirmed by photographs. Matsuki & Lien (1978) depict a much thinner, but still robust habitus for M. tenuis . The prementum is broad apically, with wide anterior lobes that may overlap at the tips and a comparatively short very narrow tear-drop shaped median cleft ( Fig. 32 ). There is normally one pair of strong seta at the base of the lobes. The caudal gills of most known species ( Fig. 45 ) are typically an elongate oval shape, about 2.5–3 times as long as broad, somewhat flattened, triquetral with no spines or tubercules on the margins or central rib in known species; the central gill is membranous and typically almost as long as the lateral gills; at its base there is a broad dorsal triangular shield that is typically as long as it is wide, but may be longer ( M. gregoryi ). Mnais gregoryi differs considerably from other species in the shape of its caudal gills, the laterals being long and tapered to a point, about five times as long as broad, whereas the median gill, which tapers to a broader rounded point, is about two thirds the length of the laterals ( Fig. 46 ).

The larvae are often found in quiet disturbed areas near the head of streams clinging to vegetation. In tropical and subtropical regions, they are chiefly montane, with M. gregoryi reaching 2500m in Yunnan, China ( Zhang 2019). Matsuki & Lien (1978) described M. tenuis as inhabiting “...low hills in northern parts of Taiwan; the larvae living in fountainhead of streams, resting on tree-roots, branches and leaves in shaded slow streams.”, and Yang et al. (2021) illustrate the habitat of M. gregoryi larva as a very shallow open stony montane stream with hydrophytes. They state that larvae are to be found clinging to these plants. The larvae of M. andersoni were found to be abundant among grass choking the head of a small open stream in a highly disturbed area at ca 1100m near Chiang Mai, Thailand (Orr, unpublished data).

Figures

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).

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).